Beat Ernst, Gerald W. Hart, Pierre Sinay
Carbohydrates in Chemistry and Biology
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Beat Ernst, Gerald W. Hart, Pierre Sinay
Carbohydrates in Chemistry and Biology Part I
Chemistry of Saccharides
VOl. 1
Chemical Synthesis of Glycosides and Glycomimetics
@WILEY-VCH Weinheim - New York * Chichester Brisbane - Singapore * Toronto
Beat Emst, Gerald W. Hart, Pierre Sinay
Carbohydrates in Chemistry and Biology Part I
Chemistry of Saccharides
VOl. 2
Enzymatic Synthesis of Glycosides and Carbohydrate-Receptor Interaction
Weinheim - New York - Chichester Brisbane - Singapore - Toronto
Beat Ernst, Gerald W. Hart, Pierre Sinay
Carbohydrates in Chemistry and Biology Part I1
Biology of Saccharides
VOl. 3
Biosynthesis and Degradation of Glycoconjugates
Weinheim - New York * Chichester Brisbane - Singapore * Toronto
Beat Ernst, Gerald W. Hart, Pierre Sinay
Carbohydrates in Chemistry and Biology Part I1
Biology of Saccharides
VOl. 4
Lectins and Saccharide Biology
@WILEY-VCH Weinheim - New York * Chichester Brisbane * Singapore * Toronto
Prof. Dr. B. Ernst Institut fur Molekulare Pharmazie Universitat Basel Klingenbergstrasse SO 4051 Basel Switzerland
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Prof. Dr. G. W. Hart Dept. of Biological Chemistry Johns Hopkins University School of Medicine 725 N. Wolf St. Rm. 401 Hunterian Baltimore, MD 21205-2185 USA ___p
Prof. Dr. P. Sinay Dept. de Chimie, URA 1686 Ecole Normale SupCrieure 24 rue Lhomond 75231ParisCedex05 France
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This book was carefully produced. Nevertheless, editors, authors and publisher do not warrant the information contained therein to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.
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Cover picture: 3,6-dideoxyhexose binding to antibody se155.4 Courtesy of David Bundle, University of Alberta
Library of Congress Card No.: applied for A catalogue record for this book is available from the British Library. Die Deutsche Bibliothek - CIP Cataloguing-in-Publication-Data A catalogue record for this publication is available from Die Deutsche Bibliothek ISBN 3-527-295 11-9
0 WILEY-VCH Verlag GmbH, D-69469 Weinheim (Federal Republic of Germany). 2000 Printed on acid-free and chlorine-free paper. All rights reserved (including those of translation in other languages). No part of this book may be reproduced in any form - by photoprinting, microfilm, or any other means - nor transmitted or translated into machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law. Composition: Asco Typesetters, Hongkong. Printing: betz-druck gmbH, D-6429 1Darmstadt. Bookbinding: Wilhelm Osswald & Co., D-67433 Neustadt. Printed in the Federal Republic of Germany.
About the Editors
Beat Ernst studied chemistry at the ETH in Zurich, Switzerland, where he completed his PhD-thesis about novel tricyclic hydrocarbons under the guidance of Professors Oskar Jeger and Camille Ganter. After his post-doctoral research on tirandamycinic acid with Professor R. E. Ireland at caltech in Pasadena, he joined the Central Research Laboratories of Ciba-Geigy (now Novartis) in Basel where he headed the Carbohydrate Research Section. In 1998 he became Professor of Molecular Pharmacy at the University of Basel, Switzerland. His major research interests are Carbohydrate Chemistry and Glycobiologymainly the chemical and enzymatic syntheses of oligosaccharides, investigation of carbohydrate/lectin interactions and carbohydrate mimics. In 1991 he was awarded the Werner-Price of the Swiss Chemical Society, and in 1993 he became CIBA-fellow for his research contributions.
Gerald Warren Hart is Director and DeLamar Professor of Biological Chemistry at Johns Hopkins University in Baltimore, MD. He studied biology, and chemistry at Washburn University and completed his PhD-thesis in developmental biology at Kansas State University before he was appointed assistant professor of Biological Chemistry at Johns Hopkins University School of Medicine. From 1993 to 1997 he held a chair at the department of Biochemistry and Molecular Genetics at the University of Alabama before he returned to Johns Hopkins University. In 1989 he founded the journal Glycobiology which became the leading journal in the field. His research results and contributions to the field of glycobiology are honored with many prices and awards-President of the Society of Glycobiology, Member of the Council of the ASBMB, First International Glycoconjugate Organization Award, just to name a few.
VI
About the Editors Pierre Sinay studied chemistry at Ecole Nationale Superieure des Industries Chimiques, Nancy, France, and received his PhD from the University of Nancy. After his post-doctoral research at Harvard University he became Professor at the University of Orleans before he was appointed professor of organic chemistry at Pierre et Marie Curie University and Ecole Normale Superieure in Paris. His main research focuses on the chemical synthesis of oligosaccharides of biological relevance and on the development of new synthetic methods in the carbohydrate field. He is Editor-in-Chief of the journal Carbohydrate Letters and he has published numerous scientific papers and patents. In 1987 he was elected president of the organic chemistry division of the French Chemical Society. In 1978 he was awarded the Le Be1 Price of the French Chemical Society, in 1996 he was triple-honoured with the Desnuelles Price, the Bethellot Medal and with the election as corresponding member of the French Academy of Sciences.
Contents
Part I
.
Vol 1
Chemistry of Saccharides Chemical Synthesis of Glycosides and Glycomimetics List of Contributors ...................................................
LV
Abbreviations Used in Volumes 1 and 2 ...........................
LXIII
I
Chemical Synthesis of Glycosides ..................................
1
1
Introduction to Volumes 1 and 2 .......................................
3
2
Trichloroacetimidates .................................................. Richard R. Schmidt and Karl-Heinz Jung Introduction ............................................................ Methods ................................................................ 0-Glycosides ............... ......................................... Synthesis of Oligosaccharides ......................................... p-Glucosides, p.Galactosides, a.Rhanmosides. etc.................... Aminosugar Trichloroacetimidates.................................... p-Mannosides ......................................................... 2-Deoxyglycosides .................................................... Miscellaneous Compounds ........................................... Complex Oligosaccharides............................................ Inositol Glycosides.................................................... Glycosylation of Sphingosine Derivatives and Mimics .............. Glycosylation of Amino Acids ....................................... Polycyclic and Macrocyclic Glycosides ..............................
5
2.1 2.2 2.3 2.3.1
2.3.2 2.3.3 2.3.4 2.3.5
5 6 7 7 7 8 13 13 14 14 36 38 40 42
VIII
Contents
2.3.6 2.3.7 2.4 2.5 2.6 2.7
Glycosides of Phosphoric and Carboxylic Acids .................... Solid-Phase Synthesis................................................. S-Glycosides .......................................................... N- and P-Glycosides.................................................. C-Glycosides.......................................................... Conclusion and Outlook ............................................. References ............................................................
3
Iterative Assembly of Glycals and Glycal Derivatives: The Synthesis of Glycosylated Natural Products and Complex Oligosaccharides... Lawrence J . Williams. Robert M . Garbaccio. and Samuel J . Danishefsky Introduction .......................................................... Ciclamycin 0 .......................................................... Allosamidin ........................................................... KS-502 and Rebeccamycin ........................................... Extension to Thioethyl Donors ...................................... LewisY ................................................................. Globo H .............................................................. KH-1 .................................................................. Concluding Remarks ................................................. Acknowledgments .................................................... References ............................................................
3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9
4
4.1 4.2 4.2.1 4.2.2 4.2.3 4.3 4.3.1 4.3.2
4.4 4.4.1 4.4.2 4.4.3
44 45 49 51 51 53 53
61
61 64 66 69 74 76 82 86 90 90 90
Thioglycosides ........................................................ 93 Stefan Oscarson Introduction .......................................................... 93 Synthesis of Thioglycosides .......................................... 94 From Anomeric Acetates............................................. 94 From Glycosyl Halides ............................................... 95 Protecting Group Manipulations in Thioglycosides ................. 96 Glycosylations with Thioglycoside Donors .......................... 97 A Two-step Procedure: Transformation of Thioglycosides into 97 Other Types of Glycosyl Donors ..................................... 99 Direct Activation of Thioglycoside Donors ......................... 99 Heavy Metal Salt Promoters ......................................... Halonium, sulfonium and carbonium type promoters ............... 100 Single-ElectronActivation ........................................... 106 Other Types of Donors With an Anomeric Sulfur .................. 108 Applications of Thioglycosides....................................... 110 Block Syntheses, Orthogonal Glycosylations ........................ 110 Thioglycosides as Acceptors.......................................... 110 Thioglycosides as Both Donors and Acceptors ...................... 111 Intramolecular Glycosidations ....................................... 112 Solid Phase Synthesis ................................................. 113 Reference6 ............................................................ 113
Contents 5
5.1 5.2 5.3 5.3.1 5.3.2 5.3.3 5.3.4 5.3.5
5.3.6 5.4 5.4.1 5.4.2 5.4.3 5.4.4
6
6.1 6.2 6.3 6.4 6.5 6.6 6.7 7
7.1 7.2 7.3 7.4 7.4.1
IX
Glycosylation Methods: Use of Phosphites ........................... 117 Zhiyuan Zhang and Chi-Huey Wong Introduction ........................................................... 117 118 Preparation of Glycosyl Phosphites .................................. Glycosylation using Glycosyl Phosphites ............................ 119 119 Mechanism ............................................................ Low Temperature-Dependent Stereoselectivity ...................... 121 Glycosylation of Sialyl Phosphites ................................... 122 Glycosylation of C-2-Acylated Glycosyl Phosphites ................. 123 Glycosylation with C-2-O-Benzylated Glycosyl Phosphites ......... 124 Glycosylation using Glucosyl Phosphites with a Benzyl Group at C-2 .................................................................... 124 Glycosylation using Galactosyl and Fucosyl Phosphites with a 125 Benzyl Group at C-2.................................................. Glycosylation using other Glycosyl Phosphites with a Benzyl Group at C-2 .......................................................... 126 Glycosylation with 2-Deoxy Glycosyl Phosphites ................... 127 128 Other Applications of Glycosyl Phosphites .......................... Synthesis of CMP-NeuAc ..... .................................... 129 Synthesis of GDP-Fucose ............................................ 129 Formation of Glycosyl Phosphonate. ................................ 131 Transformation to other Types of Glycosyl Donor ..................131 131 Phosphate ............................................................. Phosphorimidate ...................................................... 131 132 References............................................................. Glycosylation Methods: Use of n-Pentenyl Glycosides ............... 135 Bert Fraser.Reid. G. Anilkumar. Mark R. Gilbert. Subodh Joshi. and Ralf Kraehmer Introduction ........................................................... 135 Fundamental Reactions .............................................. 135 Determination of Relative Reactivities ............................... 138 n-Pentenyl Orthoesters as Glycosyl Donors .......................... 141 144 n-Pentenyl Orthoesters as Latent C2 Esters .......................... 146 Protecting Groups .................................................... Solid-Phase Iterative Couple-Deprotect-Couple Strategy .......... 146 153 References .............................................................. Glycosylidene Diazirines .............................................. Andrea Vasella. Bruno Bernet. Martin Weber. and Wolfgang Wenger Introduction ........................................................... Synthesis of Glycosylidene Diazirines ................................ Stability of the Glycosylidene Diazirines ............................. Glycosidation by Glycosylidene Diazirines .......................... General Aspects .......................................................
155 155 155 158 158 158
X 7.4.2 7.4.3 7.5 7.6 7.7
8
8.1 8.2 8.2.1 8.2.2 8.2.3 8.2.4 8.2.5 8.2.6 8.2.7 8.2.8 8.2.9 8.3 8.3.1 8.3.2 8.3.3 8.3.4 8.3.5
Contents
Glycosidation of Strongly Acidic Hydroxy Compounds ............ 162 Glycosidation of Phenols ............................................. 162 163 Glycosidation of Fluorinated Alcohols .............................. Glycosylation of Weakly Acidic Hydroxy Compounds ............. 163 163 Glycosidation of Monovalent Alcohols .............................. Glycosidation of Diols and Triols ................................... 164 Synthesis of Spirocyclopropanes ..................................... 168 Addition to Aldehydes and Ketones ................................. 170 Exploratory Use of Diazirines: Formation of Glycosyl Phosphines, Stannanes. N.Sulfonylamines. Esters. Boranes. and Alanes. and of 1.l-Difluorides ........................................................ 171 Acknowledgments .................................................... 174 174 References ............................................................ Glycosylation Methods: Alkylations of Reducing Sugars ............ 177 Jun-ichi Tamura Introduction .......................................................... 177 Anomeric O-Alkylation .............................................. 177 Anomeric O-Alkylation of Ribofuranose with Primary Triflates: Effect of the Protecting Group at 0 - 5 of Ribofuranose ............. 178 Anomeric O-Alkylation of Mannofuranose with Primary Triflates: 179 The Crown Ether Effect .............................................. Anomeric O-Alkylation of Gluco- and Galactopyranoses with Primary Triflates: High P-Selectivity as a Result of the Reactive Anomeric p-Anion .................................................... 180 Anomeric O-Alkylation of Acyl-Protected Nucleophiles with Primary Triflates ...................................................... 181 Anomeric O-Alkylation of Mannopyranose with Primary Triflates: Possibility of Intramolecular Complexation of the Nucleophile .... 184 Anomeric O-Alkylation of KDO with Primary Triflates ............ 185 Anomeric O-Alkylation of Some Protected Aldoses with Primary 186 Triflate ................................................................ Anomeric O-Alkylation of Unprotected Aldoses with Primary 187 Triflate, Bromides, and Cyclic Sulfates .............................. Anomeric O-Alkylation with Secondary Triflates and Nonaflate ... 188 Glycosylation via the Locked Anomeric Configuration ............. 189 Synthesis of Methyl. Allyl. and Benzyl Glycosides via Stannylene Acetals ................................................................ 189 Epimerization at C-2 by the Locked Anomeric Configuration 189 Method ............................................................... The Locked Anomeric Configuration Method for Rhamnosyl Stannylene Acetal ..................................................... 190 The Locked Anomeric Configuration Method for Mannosyl Stannylene Acetal: Isomerization of Acetal [25. 261 ................. 190 The Locked Anomeric Configuration Method for Stannylene Acetal with the Glucose Configuration [25. 261 ..................... 191
Contents
XI
8.4
Conclusion ............................................................ References .............................................................
9
Other Methods of Glycosylation ...................................... 195 Luigi Panza and Luigi Lay 195 Introduction and Summary ........................................... Highlights ............................................................. 195 Enol Ethers ........................................................... 197 Endo-En01 Ethers ..................................................... 198 Exo-Enol Ethers ...................................................... 201 Endo-Glycals ......................................................... 202 Exo-Glycals .......................................................... 204 Vinyl Glycosides ...................................................... 206 1-Hydroxy Sugars ..................................................... 209 Acidic Activation ..................................................... 210 Acidic Activation With Additional Reagents ........................ 211 Dehydrative Glycosylation ........................................... 212 In the Presence of the Acceptor From the Beginning ................213 214 Mitsunobu Glycosylation ............................................. I-0-Silyl Glycosides .................................................. 215 Esters and Related Derivatives ....................................... 216 216 Esters .................................................................. Sugar Carbonates and Derivatives ................................... 221 Orthoesters and Oxazolines........................................... 223 Phosphorus and Sulfur Derivatives .................................. 229 References ............................................................. 233
9.1 9.1.1 9.1.2 9.1.3 9.1.4 9.1.5 9.2 9.2.1 9.2.2 9.2.3 9.2.4 9.3 9.3.1 9.3.2 9.3.3 9.3.4
10 10.1 10.2 10.3 10.4 10.4.1 10.4.2 10.5
10.5.1
192 193
Polymer-Supported Synthesis of Oligosaccharides.................... 239 Jiri J. Krepinsky and Stephen P . Douglas Introduction ........................................................... 239 General Reflections ................................................... 240 Polymer Supports ..................................................... 246 One-Phase Systems (Syntheses in Solution) .......................... 247 248 Polyethyleneglycol,. monomethylether (MPEG) ..................... 249 Linear Polystyrene .................................................... Linkers ................................................................ 250 Succinoyl Diester ..................................................... 250 Dioxyxylyl Diether (DOX) ........................................... 252 254 Chemistry Investigations ............................................. Two-Phase Systems (Syntheses on Solid Supports) ..................255 Controlled Pore Glass ................................................ 256 256 Cross-Linked Polystyrene ............................................. Polyethylene Grafts on Cross-Linked Polystyrene. ..................256 Linkers ................................................................ 259 259 Dialkyl- or Diaryl-Silyl ............................................... Thioglycoside Linkers ................................................ 259
XI1
10.6 10.7 10.8 10.9 11 11.1 11.1.1 11.1.2
11.1.3 11.2 11.2.1
11.2.2 11.3 11.3.1
11.3.2
Contents
Linkers Cleavable by Photolysis ..................................... Examples of Syntheses ............................................... Combinatorial Libraries .............................................. Capping ............................................................... Concluding Remarks ................................................. References ............................................................
260 260 261 262 262 262
Glycopeptide Synthesis in Solution and on the Solid Phase .......... 267 Horst Kunz and Michael Schultz Introduction .......................................................... 267 Which Protecting Groups are Suitable for Carbohydrates (Table 2)? ............................................................. 269 Which Glycosylation Methods are Useful for the Formation of Glycopeptides?........................................................ 271 Formation of Asparagine N-Glycosides ............................. 271 a-Fucosylation ........................................................ 271 272 Formation of the P-Lactosamine Linkage ........................... a-Sialylation .......................................................... 272 Glycopeptides Containing Particularly Sensitive Linkages .......... 272 Acid Sensitivity ....................................................... 273 273 Base Sensitivity ....................................................... Synthesis of Glycopeptides in Solution .............................. 274 0-Glycopeptides ...................................................... 274 Glycopeptides Carrying N-Acetylgalactosamine (Tn-Antigen)...... 274 Glycopeptides Carrying the T-Antigen (Gal-GalNAc) ............. 276 Glycopeptides Carrying the Sialyl T Antigen (NeuAca2,6[Galpl,31GalNAc) ....................................... 278 279 Glycopeptides Carrying 0-GlcNAc .................................. N-Glycopeptides ...................................................... 280 N-Glycopeptides Carrying Natural Saccharide Side-Chains ........ 280 N-Glycopeptides with Lewis-Type Saccharide Side-Chains ......... 285 Glycopeptide Synthesis on the Solid Phase .......................... 286 0-Glycopeptides ...................................................... 287 Glycopeptides Carrying N-Acetylgalactosamine (Tn-Antigen)...... 287 0-Glycopeptides Carrying the T Antigen (Gal-GalNAc) .......... 290 0-Glycopeptides Carrying the Sialyl Tn Antigen (NeuNAc~a2, 6. GalNAc) .............................................................. 291 0-Glycopeptides Carrying the 2, 3.Sialyl T Antigen ................. 293 0-Glycopeptides Carrying 0-GlcNAc Side-Chains .................294 295 0-Glycopeptides Carrying 0-Linked Fucose ........................ 0-Glycopeptides Carrying a Sialyl Lewis Antigen Structure ........ 296 N-Glycopeptides ...................................................... 297 The Construction of N-Glycopeptide Libraries on the Solid 298 Phase .................................................................. Sequential N-Glycopeptide Synthesis on the Solid Phase with Oligosaccharides from Natural Sources.............................. 299
Contents
XI11
11.4
Conclusion ............................................................ References .............................................................
12
Glycolipid Synthesis ................................................... 305 Hidehuru Ishida Introduction ........................................................... 305 Synthesis of Ganglio-Series Gangliosides ............................ 305 305 Retrosynthetic Analysis of Ganglioside G D l a ...................... Preparation of Sialylgalactose Donor as Building Block ............ 306 Construction of Oligosaccharide ..................................... 308 Transformation of Oligosaccharide into Glycolipid .................310 Synthesis of Polysialo Ganglio-Series Gangliosides.................. 311 Retrosynthetic Analysis of GQl b .................................... 313 313 Preparation of Building Block ........................................ Construction of Oligosaccharide ..................................... 314 315 Conclusion ............................................................ References ............................................................. 316
12.1 12.2 12.2.1 12.2.2 12.2.3 12.2.4 12.3 12.3.1 12.3.2 12.3.3 12.4 13
13.1 13.2 13.2.1
13.2.2 13.2.3 13.2.4 13.2.5
13.2.6 13.2.7 13.2.8 13.2.9 13.3 13.4
Stereoselective Synthesis of P-Mannosides............................ Vince Pozsguy Introduction ........................................................... Chemical Methods .................................................... Glycosylation with Mannosyl Donors ............................... Mannosylation using Insoluble Promoters ........................... The Sulfonate Approach .............................................. Intramolecular Mannosylation ....................................... Other Mannosyl Donor-Based Methods ............................. Epimerization of p-Glucopyranosides at C-2 ........................ The Oxidation-Reduction Approach ................................ Direct Inversion ....................................................... The 2-Ulosyl Donor Method ......................................... Anomeric O-alkylation ............................................... Alkylation of l-O-Metal Complexes ................................. The Stannylene Acetal Method ...................................... Miscellaneous Methods ............................................... Radical Inversion of the Anomeric Chirality of a-DMannopyranosides .................................................... Reductive Cleavage of Cyclic Orthoesters ........................... De nouo Syntheses .................................................... 2-Acetamido-2-deoxy-~-~-mannopyranosides ....................... Aryl p-D-mannopyranosides.......................................... l-Thio-P-D-mannopyranosides ....................................... P-D-Mannopyranosylamines .......................................... Enzymatic Synthesis .................................................. Conclusions ........................................................... References.............................................................
300 300
319 319 320 320 320 322 324 327 329 329 329 331 332 332 332 333 333 334 334 335 336 336 337 337 338 338
XIV 14
14.1 14.2 14.3 14.4 14.4.1 14.4.2 14.4.3 14.5 14.5.1 14.5.2 14.5.3
15
15.1 15.2 15.2.1 15.2.2 15.2.3 15.2.4 15.2.5 15.2.6 15.2.7 15.3 15.4 15.5 15.5.1 15.5.2 15.5.3 15.5.4 15.6 15.6.1 15.6.2 15.6.3 15.6.4 15.6.5
Contents
Special Problems in Glycosylation Reactions: Sialidations ........... 345 Mukoto Kiso. Hidehuru Ishida and Hirorni It0 Introduction .......................................................... 345 Sialidation by the Koenigs-Knorr Method .......................... 345 347 Sialidation Using an Auxiliary Group at C-3 ....................... Sialidation Using 2.Thioglycosides. Xanthates. or Phosphites of 349 Sialic Acids in Acetonitrile ........................................... Thioglycosides ........................................................ 349 Xanthates and Phosphites ............................................ 356 359 Reaction Mechanism ................................................. Further Solutions to the Problem .................................... 359 Combination of C-3 Auxiliary and Sterically less Hindered Sugar Acceptors ............................................................. 359 Combination of C-3 Auxiliary and Specific Activation of the 360 Anomeric Center C-2 ................................................. Thioglycoside of N ,N.Diacetylneuraminic Acid and Combination 363 with C-3 Auxiliary .................................................... References ............................................................ 364 Special Problems in Glycosylation Reactions: 2-Deoxy Sugars ...... 367 Aluin Veyri2res Introduction .......................................................... 367 Electrophilic Additions to Glycals: Mechanistic Aspects and Applications to the Synthesis of 2-Deoxyglycosides . ................ 368 Protonation of Glycals ............................................... 369 370 Enzyme-Catalyzed Additions to Glycals............................. Halogenation of Glycals ............................................. 370 372 Bromo- and Iodoalkoxylation of Glycals ............................ 377 Epoxidation of Glycals ............................................... Addition of Sulfur Based Electrophiles to Glycals .................. 379 Addition of Selenium Based Electrophiles to Glycals ............... 382 The Cycloaddition Way to Glycosyl Transfer ....................... 384 385 Fluoroglycosylation of Glycals ....................................... 386 Glycosyl Donors with a C-2 Heteroatom ............................ 2-Bromo-2-deoxyglycosyl bromides .................................. 386 2-Deoxy-2-(thiophenyl)-glycosylfluorides ........................... 387 388 2,6.Anhydro-2-Thi o-Glycosyl Donors ............................... 1,2-Di-O-Acetyl-P-Hexopyranoses and N-Formylglucosamine Derivatives ............................................................ 392 2-Deoxyglycosyl Donors ............................................. 393 394 2-Deoxy-Hexopyranoses ............................................. Tert-Butyldimethylsilyl 2-Deoxyglycosides .......................... 394 1-0-Acyl- and Acetimidyl-2-Deoxy.Hexopyranoses ................. 394 395 2-Deoxyglycosyl Bromides and Fluorides ........................... S-(2-Deoxyglycosyl)phosphorodithioates............................ 396
Contents 15.6.6 15.6.7 15.6.8 5.7 5.7.1 5.7.2
6
16.1 16.2 16.2.1 16.2.2 16.3 16.3.1 16.3.2 16.3.3 16.3.4 16.4 16.4.1 16.4.2 16.4.3 16.5
17
17.1 17.2 17.3 17.4 17.5 17.5.1 17.5.2 17.6 17.7 17.8
XV
2-Deoxyglycosyl Phosphates. Phosphoramidites and Phosphites .... 397 2-Deoxy Thioglycosides .............................................. 398 399 2-Deoxyglycosyl Sulfoxides........................................... Other Approaches to 2-Deoxyglycosides............................. 400 Cyclization of Acyclic Sugars ........................................ 401 Use of Alkoxy-Substituted Anomeric Radicals ...................... 402 References............................................................. 403 Orthogonal Strategy in Oligosaccharide Synthesis ...................407 Osurnu Kun ie Introduction ........................................................... 407 Analysis of the Strategic Aspects of Oligosaccharide Synthesis ..... 408 General Aspects ....................................................... 408 The Pursuit of Efficiency in Oligosaccharide Synthesis ..............408 The Introduction of the Orthogonal Glycosylation Strategy ........ 410 Limitation of Current Concepts ...................................... 410 The Orthogonal Coupling Concept .................................. 412 413 What is Orthogonality Anyway? ..................................... Orthogonal Glycosylation and Solid-Phase Oligosaccharide 414 Synthesis .............................................................. The Orthogonal Glycosylation Strategy ............................. 414 Orthogonal Chain Elongation of Homo-Oligosaccharides: 414 Synthesis of Chito-Oligosaccharides [ 191 ............................. Orthogonal Coupling for Hetero-Oligomer Synthesis [22]...........418 Application to Polymer-Supported Synthesis [26] ...................420 421 Conclusions and Prospects ........................................... Acknowledgments .................................................... 424 References ............................................................. 424 Protecting Groups: Effects on Reactivity. Glycosylation Stereoselectivity. and Coupling Efficiency ............................ 427 Luke G. Green and Steven V. Ley Introduction ........................................................... 427 Glycosidic Mechanism ................................................ 428 Electronic and Torsional Effects ..................................... 430 Influence of Protecting Group on Donor Reactivity ................. 431 Stereoselectivity ....................................................... 436 Neighboring-Group Participation .................................... 436 437 Reactivity Control .................................................... influence of the Protecting Group on the Acceptor .................441 Steric Effects on Glycosylation ....................................... 443 444 Conclusions ........................................................... Acknowledgments .................................................... 445 References ............................................................. 446
XVI 18
18.1 18.2 18.2.1 18.2.2 18.3 18.4 19 19.1 19.2 19.2.1 19.2.2 19.2.3 19.2.4 19.2.5 19.2.6 19.3 19.3.1 19.3.2 19.3.3 19.3.4 19.3.5 19.3.6 19.4 19.4.1 19.4.2 19.4.3 19.5
Contents
Intramolecular Glycosidation Reactions .............................. 449 Jacob Madsen and Mikael Bols Introduction .......................................................... 449 Reactions in which the Tether Participates in the Reaction ......... 450 Tethering to the Glycosyl Donor .................................... 450 Carbon Tethers ....................................................... 450 Silicon Tethers ........................................................ 454 Tethering to the Leaving Group ..................................... 459 Reactions in which the Tether does not Participate in the Reaction 459 Conclusion ............................................................ 464 References ............................................................ 465 Classics In Total Synthesis of Oligosaccharides and Glycoconjugates....................................................... 467 Jean-Maurice Mallet and Pierre Sinay Introduction .......................................................... 467 Syntheses of Nod factors ............................................. 467 Introduction .......................................................... 467 The K . C . Nicolaou Synthesis (1992) [3]............................. 468 The J.-M. Beau Synthesis (1994) [ 121 ................................ 471 The T . Ogawa Synthesis (1994) [ 161 ................................. 475 The Y . Z . Hui Synthesis (1992) [ 181 ................................. 477 Conclusion ............................................................ 480 Synthesis of the Antithrombin-Binding Pentasaccharide Sequence in Heparin (1984) [ 19, 201 ............................................... 480 Introduction .......................................................... 480 An Overview of the Synthesis of the Protected Pentasaccharide 73 ..................................................................... 481 Synthesis of the Disaccharidic Bromide Donor 68 .................. 483 Synthesis of the Disaccharidic Acceptor 69 .......................... 484 Synthesis of the Protected Pentasaccharide 73 ....................... 484 Synthesis of the Active Site of Heparin .............................. 485 Total Synthesis of VIM-2 Ganglioside [31] .......................... 485 Introduction .......................................................... 485 The Total Synthesis of VIM-2-a General Strategy ................ 486 Preparation of the Key Protected Octasaccharide 87 ................ 487 Epilogue .............................................................. 490 References ............................................................ 491
I1
Synthesis of Oligosaccharide Mimics .................................
493
20
Synthesis of C-Oligosaccharides...................................... Troels Skrydstrup. Boris Vauzeilles. and Jean-Marie Beau Introduction .......................................................... The Anionic Approach ............................................... C5-Alkynyl Anions ...................................................
495
20.1 20.2 20.2.1
495 496 496
Contents
XVII
20.2.2 20.2.3 20.2.4 20.2.5 20.3 20.3.1 20.3.3 20.4 20.5
C1-Glycal Carbanions ................................................ 500 Anomeric Samarium Species ......................................... 502 C-Branched Carbanions .............................................. 506 C6-Phosphoranes ..................................................... 508 The Radical Approach ............................................... 511 Intermolecular Anomeric Radical Addition ......................... 511 513 Intramolecular Anomeric Radical Addition ......................... The Partial de Nuuo Approach ....................................... 518 The Cycloaddition and Rearrangement Approach ..................527 528 References .............................................................
21
531 Synthesis of Oligosaccharide Mimics: S-Analogs..................... Jon K. Fairweather and Hugues Driguez Introduction ........................................................... 531 General Synthesis ..................................................... 532 Preparation of Thioglycoses .......................................... 532 l-Thioglycoses ........................................................ 532 2-, 3-, 4-, 5.. or 6-Thioglycoses ....................................... 532 Selective S-Deprotection of Thioglycoses ............................ 533 Glycosylation Methods ............................................... 534 Establishment of 1,6-Thio Linkages .................................. 534 6-Thiodisaccharides ................................................... 534 6-Thiooligosaccharides ............................................... 538 538 Branched Thiocyclodextrins .......................................... Establishment of I , 4-Thio Linkages .................................. 541 1,4-Thiodisaccharides ................................................. 541 General Approaches .................................................. 541 SN~-Displacement on Triflates ....................................... 541 546 1,4-Thiooligosaccharides ............................................. Conventional Approaches ............................................ 546 548 Chemoenzymatic Approaches ........................................ 549 Michael Addition to Unsaturated Acceptors ........................ Solid-Support Synthesis........ ................................... 550 551 Establishment of 1, 3.Thio Linkages .................................. 1,3-Thiodisaccharides ................................................. 551 Conventional Methods ............................................... 551 Cyclic Sulfamidate and Aziridine .................................... 551 1,3-Thiooligosaccharides ............................................. 552 Establishment of 1,2.Thio Linkages .................................. 553 1,2-Thiodisaccharides................................................. 553 Conventional Methods ............................................... 554 Other Approaches .................................................... 555 Establishment of I , l-Thio Linkages .................................. 557 558 Establishment of Mixed Thio linkages ............................... Thiooligosaccharides and Proteins ................................... 558 The Conformation of Thiooligosaccharides in Solution ............. 558
21.1 21.2 21.2.1
21.3 21.3.1 21.3.2 21.3.3 21.4 21.4.1 21.4.2
21.5 21.5.1 21.5.2 21.6 21.6.1 21.7 21.8 21.9 21.9.1
XVIII
Contents
21.9.2
Enzyme-Substrate Interactions ...................................... a-Glucan- Active Enzymes ............................................
21.9.3 21.10
P-Glucan-Active Enzymes ............................................ Lectin-Ligand Interactions .......................................... Conclusion ............................................................ Acknowledgments .................................................... References ............................................................
22 22.1 22.2 22.2.1 22.2.2 22.3 22.4 22.4.1 22.4.2 22.4.3 22.4.4
Saccharide-Peptide Hybrids .......................................... Huns Peter Wessel Introduction .......................................................... Carbohydrate Amino Acids .......................................... Natural Carbohydrate Amino Acids ................................. Synthetic Carbohydrate Amino Acids ............................... Amide-Linked Carbohydrate Polymers .............................. Amide-Linked Carbohydrate Oligomers ............................. Solution Synthesis .................................................... Solid-Phase Synthesis................................................. Biological Activity .................................................... Conformational Properties ........................................... References ............................................................
565
Index ...................................................................
11
Part I
Chemistry of Saccharides
Vol. 2
Enzymatic Synthesis of Glycosides and CarbohydrateReceptor Interaction
111
Enzymatic Synthesis of Glycosides ..................................
23
On the Origin of Oligosaccharide Species-Glycosyltransferases in Action ................................................................ Dirk H . van den Eijnden Introduction ......................................................... Protein N-Glycosylation: Pre-assembly of Oligosaccharide-PPDolichol and en bloc Transfer ...................................... Trimming of the Polypeptide-Bound Oligosaccharide .............. Folding and Quality Control ........................................ Committed Steps in the Formation of Complex-Type Oligosaccharide Chains and Branching ............................. Topology of the Reaction Catalyzed by a Typical GlcNAcT ...... Elongation and Termination Reactions in the truns-Golgi ......... Activity with Branched Substrates ..................................
23.1 23.2 23.3 23.4 23.5 23.6 23.7 23.8
560 560 561 562 562 562 562
565 566 566 567 572 574 574 578 579 582 583
587 589 589 591 592 593 594 596 596 598
Contents
23.9 23.10 23.11 23.12 23.13 23.14 23.15 23.16 23.17 23.18 23.19 23.20 23.21 23.22 23.23 23.24 23.25 23.26 23.27 23.28 23.29 24 24.1 24.2 24.2.1
24.2.2
24.3 24.4
XIX
600 Branch Specificity .................................................... Essential Requirements for Activity with LacNAc ................. 601 Further Terminal Reactions in Complex-Type Oligosaccharide 602 Synthesis ............................................................. Specific Modifications of Polylactosaminoglycans .................. 603 The Invariable Core of N-linked Oligosaccharide Chains, and 606 Site- and Protein-Specific Processing ................................ Comparison of the Synthesis of Type 1 (Gal(P1-3)GlcNAcP-R) 607 and Type 2 (Gal(P1-4)GlcNAcP-R) Chains ........................ The LacdiN Ac Pathway of Complex-Type Oligosaccharide Synthesis ................... ....................................... 607 608 Protein O-Glycosylation ............................................. Glycosyltransferase Families ........................................ 608 610 Sialyltransferase Family ............................................. 611 a2-Fucosyltransferase Family ....................................... 612 a3/4-Fucosyltransferase Family ..................................... a3-Galactosyl/N-Acetylgalactosaminyltransferase(Histo-Blood Group ABO) Family ................................................ 613 P6-N- Acetylglucosaminyltransferase Family ........................ 613 Polypeptide N-Acetylgalactosaminyltransferase Family ............ 614 P4-N-AcetylgalactosaminyltransferaseFamily ...................... 615 P4-Galactosyltransferase Family .................................... 615 P3-Galactosyltransferase Family .................................... 617 P3-Glucuronyltransferase Family ................................... 617 Glycosyltransferases Standing Alone ................................ 617 618 Concluding Remarks ................................................ References............................................................ 618 Synthesis of Sugar Nucleotides ...................................... Reinhold Ohrlein Introduction .......................................................... Synthesis of Sugar Nucleotides ...................................... Chemical Synthesis .................................................. UDP-Activated Donors ............................................. CMP-Activated Sugars.............................................. GDP-Activated Donors ............................................. Comments ............................................................ Chemo-Enzymatic Synthesis ........................................ Uridine Diphosphate-Activated Donor Sugars ..................... CMP-Activated Sugars.............................................. GDP-activated sugars ............................................... Comments ............................................................ In situ Generation of Sugar Nucleotides ............................ Comments ............................................................ Outlook .............................................................. References............................................................
62.5 62.5 626 626 626 629 632 634 635 635 637 639 640 641 641 644 644
XX 25
25.1 25.2 25.2.1 25.2.2 25.2.3 25.2.4 25.2.5 25.2.6 25.2.7 25.3 25.3.1 25.3.2 25.3.3 25.3.4 25.4 25.5
26 26.1 26.2 26.3 26.4 26.4.1 26.4.2 26.4.3 26.4.4 26.4.5 26.5
27
27.1 27.2 27.2.1
Contents
Enzymatic Glycosylations with Glycosyltransferases ................ Ossi Renkonen Introduction ......................................................... In vitro Synthesis of the Core Region of 0.Glycans ................ Initialization of O-Glycan Biosynthesis ............................. Synthesis of Core 1 .................................................. Synthesis of Core 2 .................................................. Synthesis of Core 3 and Core 4 ..................................... In vitro Extension of Core 1 Glycans ............................... In vitro Extension of Core 2 Glycans ............................... Extension of Core 3 and Core 4 Glycans ........................... Enzymatic in vitro Synthesis of Polylactosamine Backbones ....... Enzymatic Synthesis of the Primary Chains of Blood Group i-Type ................................................................ Distal Branching of i-Type Polylactosamine Backbones ........... Central Branching of i-Type Polylactosamine Backbones.......... P4-Galactosylation in Polylactosamine Backbones ................. a3-Sialylation of N-Acetyllactosaminoglycansat the Terminal Gal a3-Fucosylation of Lactosamine Saccharides....................... References ........................................................... Recycling of Sugar Nucleotides in Enzymatic Glycosylation........ Kathryn M . Koeller and Chi-Huey Wong Introduction ......................................................... Glycosyltransferases of the Leloir Pathway and their Sugar Nucleotide Substrates ............................................... Design of Regeneration Systems .................................... Practical Regeneration Systems ..................................... UDP-Galactose ..................................................... Other UDP-Sugars .................................................. CMP-NeuAc ........................................................ GDP-Sugars ......................................................... Other Carbohydrate-Based Regeneration Systems ................. Conclusion ........................................................... References ........................................................... Enzymatic Glycosylations with Non-Natural Donors and Acceptors............................................................. Xiangping Qian. Keiko Sujino. and Monica M . Palcic Introduction ......................................................... Enzymatic Glycosylations ........................................... Galactosylations ..................................................... P 1.4-Galactosyltransferase .......................................... al.3-Galactosyltransferase ..........................................
647 647 648 648 648 649 650 650 651 651 651 652 653 654 656 656 657 659 663 663 663 665 666 666 669 671 676 680 682 683
685 685 686 686 686 688
Contents
27.2.2
27.2.3 27.2.4 27.3
28
28.1 28.2 28.3 28.3.1
28.3.2 28.4 28.4.1
28.4.2
29
29.1 29.2 29.3 29.4 29.5 29.6
XXI
Fucosylations ........................................................ Human Milk a173/4.Fucosyltransferase ............................. FucT I11 and VI ..................................................... FucT V ............................................................... Sialylations ........................................................... a2,3-Sialyltransferase and a2,6.Sialyltransferase .................... N.Acetylglucosaminylation .......................................... N-Acetylglucosaminyltransferase I, 11. and I11...................... N-Acetylglucosaminyltransferase V ................................. Summary ............................................................. Acknowledgments ................................................... References ............................................................
690 690 692 692 692 692 696 696 698 700 700 700
Solid-Phase Synthesis with Glycosyltransferases .................... Claudine AugC. Christine Le Narvor. and Andri Lubineau Introduction .......................................................... General Aspects ...................................................... Enzymatic Synthesis on Insoluble Supports ......................... Enzymatic Synthesis of Oligosaccharides ........................... Use of an Amino-Functionalized Water-Compatible Polyacrylamide Gel .................................................. Use of a Sepharose Matrix .......................................... Use of Controlled-Pore Glass ....................................... Enzymatic Synthesis of Glycopeptides .............................. Use of Controlled-Pore Glass ....................................... Use of Polyethylene Glycol Polyacrylamide (PEGA)............... Enzymatic Synthesis of Oligosaccharides and Glycoconjugates on Soluble Supports ..................................................... Enzymatic Synthesis of Oligosaccharides ........................... Use of Water-Soluble Amino-Substituted Poly(viny1 alcohol) ..... Use of Water-Soluble Glycopolymer Synthesized by Polymerization ....................................................... Enzymatic Synthesis of Glycolipids on Water-Soluble Polyacrylamide-Poly (N-acryloxysuccinimide) (PAN) .............. References ............................................................
705
Glycosidase-Catalysed Oligosaccharide Synthesis ................... David J. Vocadlo and Stephen G. Withers Introduction .......................................................... Background on Glycosidases ........................................ Basic Mechanisms ................................................... Synthesis by the ‘Thermodynamic’ Approach ...................... The Kinetic Approach ............................................... Recent Developments and New Directions ......................... References ............................................................
705 705 707 707 707 708 711 712 712 715 715 715 715 717 718 722 723 723 723 724 724 728 732 838
XXII 30
30.1 30.2 30.2.1 30.2.2 30.2.3 30.2.4 30.3 30.3.1 30.3.2 30.3.3 30.4 30.4.1 30.4.2 30.4.3
Contents
Production of Heterologous Oligosaccharides by Recombinant Bacteria (Recombinant Oligosaccharides) ........................... Roberto A . Geremia and Eric Samain Introduction ......................................................... Concept and Methodology of Heterologous (‘Recombinant’) Oligosaccharide Production in E. coli............................... Biosynthesis of Nod Factors ........................................ Expression Systems and Cloning Strategy .......................... High Cell-Density Cultivation ...................................... Purification of Recombinant Oligosaccharides ..................... Examples of Recombinant Oligosaccharides ....................... Production of Chitin Oligosaccharides in E . coli Expressing NodC ................................................................ Production of Nod Factor Precursors .............................. Production of Derivatives of N-Acetyllactosamine ................. Conclusions and Future Perspectives ............................... Production of Labeled Chitin Oligosaccharides to Study Their Interactions with Proteins ........................................... Improvement of Oligosaccharide Production, and Metabolic Engineering .......................................................... Production of More Complex Oligosaccharides .................... Acknowledgments ................................................... References ...........................................................
845 845 847 847 849 851 852 852 852 853 855 856 856 858 858 859 859
IV
Carbohydrate-Protein Interactions..................................
861
31
Protein-Carbohydrate Interaction: Fundamental Considerations ... Nikki F. Burkhalter. Sarah M . Dimick. and Eric J . Toone Introduction ......................................................... Association in Aqueous Solution ................................... Gas Phase Non Covalent Interactions .............................. Dipole-Dipole Interactions ......................................... Dipole-Induced Dipole ............................................. Dispersive Interactions .............................................. Specific Forces: Hydrogen Bonding and n - ( ~Bonding .............. The Effect of Water on Intermolecular Interactions ................ Coulombic Stabilization ............................................. Hydrogen Bonding .................................................. Dispersive Interactions .............................................. ‘Hydrophobic’ Interactions .......................................... The Evaluation of Protein-Carbohydrate Binding ................. Precipitin Assays ..................................................... Enzyme-Linked Lectin Assay (ELLA).............................. Isothermal Titration Microcalorimetry ............................. The Interpretation of Calorimetric Data ............................
863
31.1 31.2 31.2.1
31.2.2
3 1.2.3 31.3 31.3.1 31.3.2 31.3.3 31.4
863 864 864 864 866 867 868 869 870 871 872 872 876 877 878 878 882
Contents XXIII 31.4.1 3 1.4.2 31.4.3 31.5 31.6 31.6.1 31.6.2 31.6.3
32
32.1 32.2 32.3 32.4 32.5 32.6 32.7 32.8 32.9 32.9.1 32.9.2 32.9.3 32.9.4 32.10 32.10.1 32.10.2
Solvation/Desolvation ............................................... Solvation Entropy ................................................... Translational/Rotational Entropy ................................... Other Contributions to Thermodynamics of Association .......... Proton Transfer ...................................................... Salt Effects/Binding Site Reorganization ........................... van’t Hoff versus Calorimetric Enthalpies .......................... The Thermodynamics of Protein-Carbohydrate lnteraction ....... The Role of Multivalency in Protein-Carbohydrate Interaction ... Phenomenology ...................................................... The Energetic Consequence of Ligand Linkage .................... Enthalpic Contributions to AGi ..................................... Entropic Contributions to AGi ...................................... A Molecular Basis for the Cluster Glycoside Effect ................ Acknowledgments ................................................... References............................................................ Structural Analysis of Oligosaccharides: FAB.MS. ES-MS and MALDI-MS ......................................................... Anne Dell. Howard R. Morris. Richard Easton. Stuart Haslam. Maria Panico. Mark Sutton.Smitlz. Andrew J . Reason. and Kay-Hooi Khoo Introduction .......................................................... Fast Atom Bombardment-Mass Spectrometry (FAB-MS) ......... Matrix Assisted Laser Desorption Ionization-Time of Flight-Mass Spectrometry (MALDI-TOF-MS) .................................. Electrospray-Mass Spectrometry (ES-MS).......................... Appearance of Mass Spectra Obtained in FAB.MS. MALDI-MS and ES-MS Experiments ............................................ Assignment of Mass Values ......................................... Derivatisation ........................................................ Fragmentation Pathways ............................................ Protocols for MS Analysis........................................... Protocol l-Sample Loading for FAB-MS Analysis ............... Protocol 2-Sample Loading for NanoES-MS and MS-MS Analysis on the Q.TOF .............................................. Protocol 3-Sample Loading for LC-ES-MS and LC-ES-MS-MS on the Q.TOF ........................................................ Protocol 4-Sample Loading for MALDI-MS Analysis ........... Applications of FAB.MS. MALDI-MS and ES-MS in Glycobiology ......................................................... Case Study 1-Molecular Weight Profiling of Polysaccharides by MALDI-MS ......................................................... Case Study 2-Analysis of Glycoproteins by LC-ES-MS and FAB-MS .....................................................
882 883 884 885 885 885 886 887 901 901 905 906 907 910 911 911
915
915 915 917 918 919 921 921 922 924 924 925 925 925 926 926
XXIV 32.10.3 32.10.4 32.10.5 32.10.6 32.11 33 33.1 33.2 33.2.1 33.2.2 33.2.3 33.2.4 33.2.5
33.3 33.3.1 33.3.2 33.4 33.4.1 33.4.2 33.5 33.5.1 33.5.2 33.5.3 33.5.4 33.5.5 33.6 34
34.1 34.2 34.3 34.3.1
Contents Case Study 3-Characterization of a Novel N-Glycan by FAB-MS and FAB.MS.MS ......................................... Case Study 4-High Sensitivity Sequencing of a Novel Glycopeptide by Q-TOF ES-MS-MS and MALDI.MS ............ Case Study 5-FAB-MS Screening of Biological Samples for Glycan Content ...................................................... Case Study 6-MS Analysis of Mycobacterial Glycoconjugates . . Concluding Remarks ................................................ References ........................................................... Conformational Analysis in Solution by NMR ...................... S. W. Homans Introduction ......................................................... Solution Conformations of Oligosaccharides ....................... The NMR Technique ................................................ Conformational Parameters in Oligosaccharides ................... Conformational Restraints .......................................... I3C Isotopic Enrichment ............................................ Additional Conformational Restraints .............................. Exchangeable Protons ............................................... Heteronuclear Overhauser Effects................................... 13C- c Coupling-Constants ....................................... Dipolar Couplings ................................................... Experimental Restraints in Conformational Analysis .............. Restraining Protocol ................................................. Biharmonic Restraints ............................................... Time-Dependent Restraints ......................................... Dynamical Simulated Annealing .................................... Analysis of Oligosaccharide Dynamics ............................. Monte-Carlo Simulations ........................................... Molecular Dynamics Simulations ................................... A Case Study on Neu5Aca2-3GalP1-4Glc ......................... Resonance Assignments in Neu5Aca2-3Galfll-4Glc ............... ROE Connectivities ................................................. ‘Global Minimum’ Conformation of Neu5Aca2-3GalP1-4Glc .... Conformational Dynamics of Neu5Aca2-3Gal~1-4Glc............ Short-range vs Long-range Restraints .............................. Conclusions .......................................................... References ........................................................... Oligosaccharide Conformations by Diffraction Methods ............ Serge Pdrez. Catherine Gautier. and Anne Imberty Introduction ......................................................... General Analysis .................................................... Crystalline Conformations of Disaccharide Moieties .............. The Disaccharides ...................................................
930 933 935 942 944 945 947 947 947 947 948 949 949 950 950 952 953 954 955 955 955 957 957 958 959 959 959 960 960 961 962 963 966 966 969 969 970 973 973
Contents 34.3.2 34.4 34.5 34.6 34.7 34.8
35 35.1 35.2 35.3 35.4 35.5 35.6 35.7 35.8 36
36.1 36.2 36.3 36.4 36.5 36.6 36.7 36.8 36.9
37 37.1 37.1.1 37.1.2 37.2
XXV
The Analogs (S. C. N. ....). ......................................... Hydrogen Bonding in Crystalline Oligosaccharides ................ Packing Features ..................................................... Selected Examples ................................................... Crystalline Conformations of Oligosaccharides Complexed with Lectins................................................................ Concluding Remarks ................................................ References ............................................................
985 987 988 990 992 996 998
Transfer NOE Experiments for the Study of Carbohydrate-Protein Interactions ........................................................... 1003 Thomas Peters Introduction .......................................................... 1003 1004 The Transfer NOE Experiment ..................................... 1006 Measurement of trNOEs .......................................... Bioactive Conformations of Carbohydrate Ligands From trNOE Experiments .......................................................... 1008 Spin Diffusion may Generate Misleading Distance Constraints ... 1009 The Conformation of Sialyl Lewis' Bound to E-selectin ...........1011 Interaction of Bacterial Lipopolysaccharide Fragments with Monoclonal Antibodies .............................................. 1016 Conclusions and Future Directions ................................. 1019 References ............................................................ 1021 Carbohydrate-Protein Interactions: Use of the Laser Photo Chemically Induced Dynamic Nuclear Polarization(C1DNP)-NMR Technique ............................................................ 1025 Hans-Christian Siebert and Johannes F. G. Vliegenthart Introduction .......................................................... 1025 The CIDNP Method ................................................. 1026 CIDNP-related Molecular Modelling ............................... 1027 Applications .......................................................... 1027 Hevein-like Lectins .................................................. 1029 Galactoside-binding Lectins from Plant and Animal Origin ....... 1032 Sialidase from Clostridium Perfringens (Wild Type and Mutants) . 1037 CIDNP Analysis of Glycoproteins .................................. 1039 Conclusions .......................................................... 1040 Acknowledgments ................................................... 1041 1042 References ............................................................ Biacore ............................................................... 1045 Wolfgang Jager Introduction .......................................................... 1045 Real-time Analysis by Surface Plasmon Resonance ................1045 Information in a Sensorgram ........................................ 1047 Experimental Procedures ............................................ 1048
XXVI
Contents
37.2.1 31.2.2 37.2.3 37.2.4 37.2.5 37.3 37.3.1 37.3.2 37.3.3
Immobilization of Biomolecules at the Sensor Surface ............. 1048 Surface Regeneration ................................................ 1050 Interaction Analysis and Controls .................................. 1051 1052 Determination of Kinetic Rate Constants .......................... Affinity Determination .............................................. 1053 1054 Application Areas ................................................... Selectin Binding to a Glycoprotein Ligand ......................... 1054 Oligosaccharide Characterization ................................... 1055 In situ Modification of Immobilized Carbohydrates ................1056 References ........................................................... 1056
V
Carbohydrate-Carbohydrate Interactions ...........................
38
Carbohydrate-Carbohydrate Interactions ........................... 061 Dorothe Spillmann and Max M . Burger Introduction ......................................................... 1061 From Structural Components to Cell Recognition ................. 1063 Carbohydrate-Carbohydrate Interactions as Part of Structural Components ......................................................... 1063 Extracellular Matrix of Seaweeds-Agarose, Carrageenan and 1063 Alginate .............................................................. Cell Walls ............................................................ 1064 Mammalian Extracellular Matrix Components .................... 1066 Carbohydrate-Carbohydrate Interactions as Part of Recognition 1068 Keys? ................................................................. Carbohydrate Interactions in Invertebrates-The Marine Sponge Microciona prolifera as a Model System ............................ 1069 Carbohydrate Interactions in Vertebrates-Embryonal and Tumor 1071 Cells .................................................................. Repulsive Carbohydrate-Carbohydrate Interactions ............... 1072 Molecular Aspects of Carbohydrate Interactions ...................1074 1074 Polyvalence to Inforce Weak Interactions .......................... Arrangement of Motifs and the Possibility to Control Specificity . 1075 Molecular Basis of Carbohydrate-Carbohydrate Interactions ..... 1076 Experimental Approaches ........................................... 1078 General Considerations ............................................. 1078 Affinity Interactions ................................................. 1079 1079 Cell Binding Studies ................................................. Aggregation of de n o w Complexes ................................. 1081 Affinity Chromatography ........................................... 1082 Distribution between Compartments ............................... 1082 Microscopy .......................................................... 1083 Electron Microscopy ................................................ 1083 Atomic Force Microscopy .......................................... 1083 1084 Crystallography ......................................................
38.1 38.2 38.2.1
38.2.2
38.3 38.3.1 38.3.2 38.3.3 38.4 38.4.1 38.4.2
38.4.3 38.4.4
059
Contents XXVII
38.4.5 38.4.6 38.4.7 38.4.8
Mass Spectrometry .................................................. Nuclear Magnetic Resonance ....................................... Molecular Modelling ................................................ Tools ................................................................. Synthetic Oligosaccharides .......................................... Antibodies against Carbohydrate Motifs ........................... Cells .................................................................. References ............................................................
1085 1085 1086 1086 1086 1087 1088 1088
V1
Carbohydrate-Nucleic Acid Interactions ............................
1093
39
Carbohydrate-Nucleic Acid Interactions ............................ Heinz E . Moser Introduction .......................................................... Carbohydrates Binding to DNA .................................... Ene-Diyne Antibiotics and Antitumor Agents ...................... Esperamicins ......................................................... Calicheamicins ....................................................... Anthracyclins ........................................................ Pluramycins and Aureolic Acids .................................... Carbohydrates Binding to RNA .................................... Aminoglycosides ..................................................... References ............................................................
1095
39.1 39.2 39.2.1 39.2.2 39.2.3 39.3 39.3.1
Index ...................................................................
Part I1
Biology of Saccharides
Vol . 3
Biosynthesis and Degradation of Glycoconjugates Introduction to Volumes 3 and 4 ....................................... Abbreviations Used in Volumes 3 and 4 .............................
1095 1096 1096 1096 1100 1106 1111 1112 1113 1120 11
V LV
I
Biosynthesis of Glycoconjugates .......................................
1
1
Metabolism of Sugars and Sugar Nucleotides ......................... Hudson H . Freeze Introduction ............................................................ Basic Principles ........................................................ Transporters Deliver Monosaccharides to Cells ...................... Intracellular Sources of Sugars ........................................ Salvage .................................................................
3
1.1 1.2 1.3 1.4 1.4.1
3 3 4 5 5
XXVIII Contents 1.4.2
1.5 1.6 1.7 2
2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10
3
3.1 3.2 3.3 3.4 3.5
Activation and Interconversion of Monosaccharides................. Glycogen ............................................................... Glucose ................................................................ Glucuronic acid ........................................................ Iduronic acid ........................................................... Xylose .................................................................. Mannose ............................................................... Fucose .................i ............................................... Galactose ............................................................. N-Acetylglucosamine................................................. N-Acetylgalactosamine............................................... Sialic acids ............................................................ Sugar Nucleotide Transporters ....................................... Control of Sugar Nucleotide Levels ................................. Possible Future Directions ........................................... References ............................................................
6 6 7 8 8 8 8 9 10 10 10 11 11 13 13 14
Nucleotide Sugar Transporters ....................................... Rita Gerardy-Schahn and Matthias Eckhardt Introduction .......................................................... General Considerations .............................................. The Requirement for Nucleotide Sugar Transporters and Their Mechanism of Function: A Comprehensive Overview of the Last 20 Years .............................................................. Molecular Cloning of Nucleotide Sugar Transporters .............. The Structure of Nucleotide Sugar Transporters .................... The Subcelluar Distribution of Nucleotide Sugar Transporters ..... Molecular Defects that Cause Inactive UDP-Galactose and CMP-Sialic Acid Transporters ....................................... Association Between Defects in Nucleotide Sugar Transporters and Diseases ............................................................... Involvement of Nucleotide Sugar Transporters in the Regulation of Glycosylation ......................................................... Future Perspectives ................................................... Acknowledgements ................................................... References ............................................................
19
Biosynthesis of Oligosaccharyl Dolichol .............................. Sharon S. Krag General Overview .................................................... Oligosaccharyl Dolichol .............................................. Key Enzymatic Steps in the Assembly Process ...................... Topology of the Assembly Process................................... Utilization of Oligosaccharyl Dolichol .............................. Acknowledgment ..................................................... References ............................................................
19 20
20 22 25 27 28 29 29 30 31 32 37 37 38 39 42 42 43 43
Contents XXIX 4
4.1 4.2 4.2.1 4.2.2 4.2.3 4.2.4 4.3 4.4 4.4.1 4.4.2 4.4.3 4.4.4 4.4.5 4.4.6 4.4.7 4.4.8 4.5
5
5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8
6
6.1 6.2
Biochemistry and Molecular Biology of the N-Oligosaccharyltransferase Complex................................................... Roland Knauer and Ludwig Lehle Introduction ........................................................... Biochemistry of OST ................................................. Lipid-Saccharide Donor ............................................. Acceptor Specificity of OST .......................................... Catalytic Mechanism of OST ........................................ Regulation of OST Activity .......................................... Isolation of OST Complexes from Different Sources ................ Molecular Biology of OST ........................................... WBPl/OST48 ......................................................... SWPl/Ribophorin I1 ................................................. OSTl/Ribophorin I ................................................... OST3/OST6 ........................................................... OST5 .................................................................. OST4 .................................................................. OST2/DAD1 .......................................................... STT3 .................................................................. Structural Organization of the OST Complex ....................... Acknowledgments .................................................... References ............................................................. Processing Enzymes Involved in the Deglucosylation of N-Linked Oligosaccharides of Glycoproteins: Glucosidases I and 11 and Endomannosidase ..................................................... Robert G. Spiro Introduction ........................................................... Glucosidase I .......................................................... Glucosidase 11......................................................... Endo-a-mannosidase .................................................. Concerted Action of Deglucosylation Enzymes ...................... Mutants ............................................................... Role of Monoglucosylated N-Linked Oligosaccharides and Glucose Trimming Enzymes in Regulating Quality Control of Glycoproteins ......................................................... Effect of Glucosidase Inhibitors on Viral Proliferation .............. Acknowledgments .................................................... References............................................................. a-Mannosidases in Asparagine-linked Oligosaccharide Processing and Catabolism ........................................................ Kelley W. Moremen Overview .............................................................. Introduction ...........................................................
45 45 46 47 48 49 51 51 52 54 54 55 55 56 56 57 58 59 60 60
65 65 66 68 70 72 74
75 77 78 78
81 81 82
XXX 6.2.1 6.2.2 6.2.3 6.2.4 6.2.5 6.3 6.3.1 6.3.2
6.3.3
6.4
7 7.1 7.2 7.3 7.4 7.5
8 8.1 8.2
Contents
Roles of N - and O-Linked Glycans and Compartmentalization of Biosynthetic and Catabolic Reactions ............................... 82 82 Processing of Asn-Linked Oligosaccharides ......................... Early Trimming Events: importance for quality control glycoprotein degradation and anteriograde transport ..................... 85 Glycoprotein Catabolism: multiple routes for glycoprotein 87 breakdown ............................................................ Consequences of Genetic Defects in Oligosaccharide Biosynthesis and Catabolism ....................................................... 88 Mannosidases in Glycoprotein Processing and Catabolism ......... 89 89 Classification of Mannosidases ....................................... Class 1 Mannosidases: enzymes of the ER and Golgi ............... 93 ER mannosidase I subfamily ......................................... 93 95 Golgi mannosidase I sub-family ..................................... Fungal secreted mannosidases ....................................... 97 New genes with unknown functions ................................. 98 Class 2 Mannosidases: enzymes of the cytosol, ER, Golgi, and Lysosomes ............................................................ 98 99 Golgi mannosidase I1................................................. Lysosomal mannosidase ............................................. 101 Epididymal/sperm mannosidase .................................... 103 Heterogeneous cluster of mannosidase homologs among eukary a, 104 eubacteria, and archaea ............................................. Conclusions and Future Prospects .................................. 106 107 Acknowledgments ................................................... 107 References ........................................................... The Role of UDP-Glcyglycoprotein Glucosyltransferase as a Sensor of Glycoprotein Conformations ...................................... Armando J. Parodi Introduction ......................................................... General Properties ................................................... GT Recognizes Glycoprotein Conformations ...................... The Primary Structure of the UDP-Glcyglycoprotein Glucosyltransferase .................................................. The Role of Monoglucosylated Oligosaccharides in Glycoprotein Folding ............................................................... Acknowledgments ................................................... References ........................................................... Mannosyltransferases................................................ Peter Orlean Introduction ......................................................... Occurrence of Covalently-linked Mannose .........................
119 119 120 121 122 123 126 127 129 129 130
Contents XXXI
8.2.1 8.2.2 8.2.3 8.2.4 8.3 8.3.1 8.3.2 8.3.3 8.3.4 8.4 8.4.1
8.4.2
8.4.3 8.4.4 8.5 8.6
9
9.1 9.2 9.3 9.3.1 9.3.2 9.4 9.5 9.6
Eukaryotic Secretory Glycoproteins ................................ Glycophospholipids .................................................. Eubacterial and Archaeal Mannose-containing Molecules ......... C-linked Mannose ................................................... Biochemistry of Mannosyl Transfer ................................. Many Linkages, Two Donors ....................................... Donor Specificity .................................................... Acceptor Specificity.................................................. Structural Features of Man-T ....................................... Man-T Families and the Pathways They Participate in ............ Man-Ts of the ER [l-51 ............................................. Alglp ................................................................. Alg2p/Algl l p ........................................................ Dpmlp ............................................................... Alg3p ................................................................. Alg9p/PIG-Bp family ................................................ Pmtlp family ......................................................... Golgi Man-Ts and Fungal Mannan Synthesis ...................... Ochlp family ......................................................... ................................. Mnn9p family ........... MnnlOp/Mnnl l p family ............................................ Mnnlp family ........................................................ Ktrlp family ......................................................... “Missing” Eukaryotic Man-T ....................................... Eubacterial and Archaeal Man-T ................................... Coordinating Man Transfer with the Cell Cycle and Morphogenesis ....................................................... Concluding Remarks ................................................ Acknowledgments ................................................... References............................................................
130 130 130 130 131 131 131 132 132 133 134 134 134 135 135 135 136 136 137 137 138 138 138 138 139
Branching of N-Glycans: N-Acetylglucosaminyltransferases........ Hurry Schuchter Introduction .......................................................... Processing of N-Glycans within the Endomembrane Assembly Line .................................................................. General Properties of the N-Acetylglucosaminyltransferases....... Domain Structure .................................................... Targeting to the Golgi Apparatus ................................... UDP-GlcNAc:Manal-3R [GlcNAc to Manwl-31 p.1,2. N . Acetylglucosaminyltransferase I (GnT I, EC 2.4.1.101) ............ UDP-GlcNAc:Manal-6R [GlcNAc to Manal-61 p.1,2. N . Acetylglucosaminyltransferase 11 (GnT 11, E.C. 2.4.1.143). ........ The Role of GnT I and I1 in Mammalian Development ...........
145
139 140 140 140
145 146 148 148 150 150 152 153
XXXII 9.7 9.7.1 9.7.2 9.8 9.9 9.9.1 9.10 9.11
10 10.1 10.2 10.2.1 10.3 10.3.1 10.3.2 10.3.3 10.3.4 10.3.5 10.4 10.4.1 10.4.2 10.4.3 10.4.4 10.5 10.5.1 10.5.2 10.5.3 10.5.4
Contents UDP-G1cNAc:RI-Manal-6[GlcNAc~l-2Manul-3]Man~l-4R~ [GlcNAc to ManP 1-41 P- 1,4. N.Acetylglucosaminyltransferase 111 155 (GnT 111. E.C. 2.4.1.144). ........................................... 156 Overexpression of GnT 111 Activity ................................. 157 GnT 111 Activity and Cancer ........................................ UDP-GlcNAc:R1Manal-3R2 [GlcNAc to Manal-31 (3.1,4. N . Acetylglucosaminyltransferase IV (GnT IV, E.C. 2.4.1.145). ...... 157 UDP-GlcNAc:Rl Manal-6R2 [GlcNAc to Manal-61 P-1,6-NAcetylglucosaminyltransferase V (GnT V, E.C.2.4.1.155) ......... 158 159 GnT V Activity and Cancer ......................................... UDP-GlcNAc:Rl (R2)Manal-6R3 [GlcNAc to Manul-61 P-1, 4-Nl -Acetylglucosaminyltransferase VI (GnT VI) ............. 161 161 GnT VII and GnT VIII ............................................. 162 References ........................................................... The Galactosyltransferases .......................................... Nancy L . Shaper. Martin Charron. Neng- Wen Lo. Jane R. Scocca. and Joel H . Shuper Introduction ......................................................... Using the Databanks to Obtain Information on the Galactosyltransferases ............................................... Nomenclature ........................................................ The Dual Role of P4-Galactosyltransferase-I (P4GalT-I) in Oligosaccharide and Lactose Biosynthesis: The Early Days ....... p4GalT-I: Isolation and Characterization of cDNA Clones ....... The Murine NGalT-I Gene: Genomic Organization and Structure of the 5'-End ......................................................... P4GalT-I and Lactose Biosynthesis ................................. P4GalT-I and the Vertebrate P4GalT Gene Family ................ Evolution of the 04-Galactosyltransferase Gene Family ........... The Vertebrate P3Galactosyltransferase (P3GalT) Gene Family . . General Characteristics of the P3-Galactosyltransferase Gene Family Members .................................................... P3GalT-IV: UDP-ga1actose:GM 1 P3-galactosyltransferase (GM1 Synthase; GalT-3) ................................................... Other Vertebrate P-Galactosyltransferase Activities................ UDP-Ga1actose:Ceramide P-Galactosyltransferase (CGalT; EC 2.4.1.45). ............................................................. The Vertebrate u3-Galactosyltransferase Gene Family ............ u3-Galactosyltransferase (a3GalT: UDP-Gal:Galp4GlcNAca3Galactosyltransferase; EC 2.4.1.87) ................................. The Blood Group B a3-Galactosyltransferase (EC 2.4.1.37). ...... The Forssman Glycolipid Synthetase (EC 2.4.1.88). ............... Evolution of the u3GalT Gene Family .............................
175 175 177 177 178 181 181 182 182 184 185 186 187 187 187 188 188 190 191 191
Contents XXXIII
10.6
A UDP-Gal:Gal@3GalNAca4Galactosyltransferase Activity ..... 192 192 Acknowledgments ................................................... References............................................................ 192
11
Fucosyltransferases ................................................... 197 Ernest0 T. A . Marques. Jr. Introduction .......................................................... 197 198 General Characteristics .............................................. Nomenclature ........................................................ 198 199 Gene Structure ....................................................... Sequence Peptide Motifs ............................................. 199 Specificity ............................................................ 199 200 Protein Structure and Topology ..................................... Enzymatic Reaction Mechanism .................................... 201 203 Inhibitors ............................................................. 203 Specific Fucosyltransferases ......................................... GDP-Fucose: Fucal (Fucal,2Fuc)a2-fucosyltransferase ............ 204 GDP-Fucose: GalPl (Fucal,2Gal)a2-fucosyltransferase ............ 204 GDP-Fucose: Gal~l,4/3GlcNAc(Fucal,3/4GlcNAc)a3/ 4204 fucosyltransferases ................................................... 204 Blood group Lewis: FucT 111, V and VI ............................ Myeloid enzyme: FucT IV ........................................... 205 Leukocyte enzyme: FucT VII ....................................... 206 206 Neuronal enzyme: FucT IX ......................................... GDP-Fucose: Gal~l,3GlcNAc(Fuca1, 3GlcNAc) bacterial (Helicobacter pylori) a3-fucosyltransferase ......................... 207 GDP-Fucose: GlcNAc-N(Fuca1,6GlcNAc)a6fucosyltransferases . 207 GDP-Fucose: O-Ser(Fuca1-O-Ser)GlcNAc polypeptide 207 fucosyltransferases ................................................... Unconventional Types of Fucosylation: FucPl -P-Ser and cytoplasmic Fucal,2-GalP1,3-GlcNAc-Pro (Dictyostelium discoideum) 207 FucP 1-P-Ser .......................................................... 207 208 Fucal,2-GalP1,3-GlcNAc-Pro ...................................... Acknowledgments ................................................... 208 208 References............................................................
11.1 11.2 11.2.1 11.2.2 11.2.3 11.2.4 11.2.5 11.2.6 11.2.7 11.3 11.3.1 11.3.2 11.3.3
11.3.4 11.3.5 11.3.6 11.3.7
12
12.1 12.2 12.3 12.4 12.5 12.6 12.7
Sialyltransferases..................................................... Joseph T. Y. Lau and Sherry A . Wuensch Introduction .......................................................... General Features of Sialyltransferases .............................. Cloning and ldentification Strategies for Sialyltransferases ........ Sialyltransferase Classification and Nomenclature .................. The a2, 3-ST Family ................................................. The 1x2,6-ST Family ................................................. The 1x2.8.ST Family .................................................
213 213 213 215 216 216 217 218
XXXIV Contents 12.8
Regulation and Functionality of Sialyltransferases................. 219 221 References ...........................................................
13
Biochemistry of Sialic Acid Diversity................................ Roland Schauer Introduction ......................................................... Occurrence and Biosynthesis ........................................ General Biological Functions ....................................... N-Glycolylneuraminic Acid ......................................... 0-Acetylated Sialic Acids ........................................... 0-Methylated and 0-Sulfated Sialic Acids ......................... Acknowledgments ................................................... References ...........................................................
13.1 13.2 13.3 13.4 13.5 13.6
14 14.1 14.2 14.3 14.4 14.5 14.6 14.7
15
15.1 15.2 15.3 15.4 15.5 15.6 15.7 15.8 15.9 15.10
Carbohydrate Sulfotransferases...................................... Steven D. Rosen. Annette Bistrup. and Stefan Hemmerich Introduction ......................................................... Basic Features of Sulfotransferase Reactions ....................... Tyrosine Sulfation ................................................... Diversity of Carbohydrate Sulfation ................................ Biochemical Demonstration of Carbohydrate Sulfotransferases ... Molecular Cloning of Carbohydrate Sulfotransferases ............. Primary Structures of Carbohydrate Sulfotransferases ............. Acknowledgments ................................................... References ........................................................... Novel Variant Pathways in Complex-type Oligosaccharide Synthesis ............................................................. Dirk H . van den Eijnden Introduction ......................................................... The lacNAc Pathway of Complex-type Oligosaccharide Synthesis Occurrence and Biology of 1acdiNAc-based Complex-type Oligosaccharides ..................................................... Biosynthesis of lacdiNAc Backbone Units .......................... The lacdiNAc Pathway of Complex-type Oligosaccharide Synthesis ............................................................. Other Shared Properties of 04-GalT and 04-GalNAcT ............ Cloning of a snail UDP-G1cNAc:GlcNAcP-R 04-Nacetylglucosaminyltransferase ....................................... The Chitobio Pathway of Complex-type Oligosaccharide Synthesis ............................................................. Competition Between Pathways ..................................... Concluding Remarks ................................................ References ...........................................................
227 227 227 229 231 234 238 239 239 245 245 245 246 246 249 250 252 256 256
261 261 261 262 263 264 266 266 267 267 269 269
Contents XXXV 16
16.1 16.2 16.3 16.4 16.4.1 16.4.2
16.5 16.6 16.7
17
17.1 17.2 17.2.1 17.2.2 17.2.3 17.2.4 17.2.5 17.3
Control of Mucin-Type 0-Glycosylation: 0-Glycan Occupancy is Directed by Substrate Specificities of Polypeptide GalNAcTransferases .......................................................... 273 Helle Hassan. Eric P. Bennett. Ulla Mandel. Michael A . Hollingsworth. and Henvik Cluusen Introduction .......................................................... 273 The Mammalian UDP-GalNAc: Polypeptide GalNAc-Transferase Gene Family ......................................................... 274 The GalNAc-Transferase Gene Family is Evolutionarily Old ..... 276 The Kinetic Properties of GalNAc-Transferase Isoforms are Different.............................................................. 278 Lessons from in vivo Analysis of GalNAc-transferase Substrate Specificities ........................................................... 219 Lessons from in vitro Analysis of the Acceptor Substrate Specificities of GalNAc-transferase Isoforms ....................... 280 Isoforms may have distinct acceptor substrate specificities ......... 281 Isoforms may have overlapping substrate specificities .............. 283 Isoforms may act in different order on substrates with multiple 283 acceptor sites ......................................................... Isoforms may require prior (GalNAc) glycosylation ............... 283 Expression of the GalNAc-Transferase Genes are Differentially Regulated ............................................................ 285 288 Predictive Value of in vitro 0-glycosylation? ....................... Conclusions and Future Perspectives................................ 288 References ............................................................ 289 Glycosyltransferase Inhibitors ........................................ Xianyping Qian and Monica M . Palcic Introduction .......................................................... Inhibitors of Glycosyltransferases................................... Inhibitors of Galactosyltransferases ................................. Inhibitors of pl, 4-galactosyltransferase ............................. Inhibitors of cr.l,3-galactosyltransferase............................. Inhibitors of Fucosyltransferases .................................... Inhibitors of 1x1,2-fucosyltransferases ............................... Inhibitors of a1,3-fucosyltransferases ............................... Inhibitors of Sialyltransferases ...................................... Inhibitors of a2, 6-sialyltransferase .................................. Inhibitors of a2, 3.sialyltransferase .................................. Inhibitors of N-Acetylglucosaminyltransferases .................... Inhibitors of Human Blood Group A and B Glycosyltransferases. Summary ............................................................. Acknowledgments ................................................... References............................................................
293 293 296 296 296 297 298 300 300 301 302 304 305 306 309 309 309
XXXVI Contents 18
18.1 18.2 18.3 18.4 18.5 18.6 18.7 18.8 18.9 18.10 18.11 18.12
19
19.1 19.2 19.3 19.4 19.5 19.6 19.7
20
20.1 20.2 20.3 20.3.1 20.3.2 20.3.3 20.3.4 20.3.5 20.4 20.4.1 20.4.2 20.4.3 20.5
Biosynthesis of the O-Glycan Chains of Mucins and Mucin Type Glycoproteins ........................................................ Inka Brockhausen Summary ............................................................. Introduction ......................................................... Structures of O-Glycans ............................................. Functions of Much Type O-Glycans ............................... Primary O-Glycosylation ............................................ Synthesis of O-Glycan Core 1....................................... Synthesis of O-Glycan Core 2 ....................................... Synthesis of O-Glycan Core 3 ....................................... Synthesis of O-Glycan Core 4 ....................................... Synthesis of O-Glycan Cores 5-8 ................................... Elongation and Branching Reactions ............................... Synthesis of Terminal Structures .................................... Acknowledgments ................................................... References ........................................................... Glycosyltransferases in Glycosphingolipid Biosynthesis ............. Subhash Basu. Kamal Das. and Manju Basu Introduction ......................................................... Fucosyltransferases in Glycolipid Biosynthesis ..................... Galactosyltransferases in Glycolipid Biosynthesis .................. N-Acetylgalactosaminyltransferases in Glycolipid Biosynthesis.... N-Acetylglucosaminyltransferases in Glycolipid Biosynthesis...... Sialyltransferases in Glycolipid Biosynthesis ....................... Glucuronyltransferases in Glycolipid Biosynthesis ................. Acknowledgments ................................................... References ........................................................... Biosynthesis of Glycogen ............................................ Peter J . Roach Summary ............................................................. Introduction ......................................................... Glycogenin and the Initiation of Glycogen Synthesis .............. History ............................................................... Properties ............................................................ Reaction Mechanism ................................................ Domain Structure ................................................... Function ............................................................. Glycogen Synthase and the Bulk Synthesis of Glycogen ........... Properties ............................................................ Structure of Glycogen Synthase ..................................... Branching Enzyme .................................................. Intermediates in the Biosynthesis of Glycogen .....................
313 313 313 314 314 315 315 317 319 319 319 320 321 324 324 329 329 329 332 334 336 337 340 342 342 349 349 350 351 351 351 352 352 354 354 354 355 356 357
Contents XXXVII 20.6
Conclusion ........................................................... Acknowledgments ................................................... References ............................................................
358 359 359
21
Biosynthesis of Hyaluronan .......................................... Paraskevi Heldin and Torvard C. Laurent Introduction .......................................................... Site of Biosynthesis .................................................. Biosynthetic Precursors .............................................. Hyaluronan Synthases ............................................... Microbial Enzymes .................................................. Vertebrate Synthases ................................................. Mechanism of Synthesis ............................................. Chain Elongation .................................................... Translocation ........................................................ Shedding ............................................................. Regulation of HA Synthesis ......................................... Concluding Remarks ................................................ Acknowledgments ................................................... References ............................................................
363
21.1 21.2 21.3 21.4 21.4.1 21.4.2 21.5 21.5.1 21.5.2 21.5.3 21.6 21.7
22
22.1 22.2 22.2.1 22.2.2 22.2.3 22.2.4 22.3 22.3.1 22.3.2 22.3.3
22.3.4
Biosynthesis of Chondroitin Sulfate and Dermatan Sulfate Proteoglycans ........................................................ Geetha Sugumaran and Barbara A4. Vertel Introduction .......................................................... Proteoglycan Structure .............................................. Proteoglycans and Their Core Proteins ............................. What Initiates GAG Chain Addition? .............................. The Linkage Region ................................................. .................................... CS and DS Chains ........... Biosynthesis of CS and DS Proteoglycans .......................... Biosynthesis of the Core Protein .................................... Origin of Sugar and Sulfate Precursors ............................. Addition of the Linkage Oligosaccharides .......................... Xylosylation .......................................................... Galactosylation ...................................................... Addition of GlcA and completion of the common tetrasaccharide linkage region ........................................................ Initiation of CS/DS chains by addition of the first GalNAc ....... Formation of the CS/DS Chains .................................... Addition of the repeating disaccharides ............................. Epimerization of GlcA to IdoA to form DS ........................ Sulfation of GalNAc................................................. Sulfation of uronic acid ..............................................
363 364 364 365 365 366 367 368 369 369 370 371 372 372
375 375 379 379 381 381 382 383 383 384 385 385 386 387 388 388 388 389 390 391
XXXVIII Contents 22.4
Concluding Remarks/Perspectives .................................. Acknowledgments ................................................... References ...........................................................
391 392 392
23
Biosynthesis of Heparin and Heparan Sulfate Proteoglycans ....... Lena Kjellin and U r Lindahl Introduction ......................................................... The Proteoglycans: Structure. Location and Functions ............ Biosynthesis of the Polysaccharide Backbone ...................... Outline of Polymer-Modification Reactions ........................ The N.Deacetylase/N.Sulfotransferases ............................. The C5-Epimerase ................................................... The 2-O-Sulfotransferase............................................ The 6-O-Sulfotransferases........................................... The 3 - 0 Sulfotransferases........................................... The Products. Heparin and Heparan Sulfate ....................... Interactions with Proteins ........................................... Regulation of HS Biosynthesis ...................................... References ...........................................................
395
23.1 23.2 23.3 23.4 23.4.1 23.4.2 23.4.3 23.4.4 23.4.5 23.5 23.6 23.7
24 24.1 24.2 24.2.1 24.2.2 24.2.3 24.2.4 24.3 24.3.1 24.3.2 24.3.3 24.3.4 24.4 24.5
25
25.1 25.2 25.2.1
395 396 396 397 399 399 399 400 400 400 401 402 403
Biosynthesis of Proteoglycans with Keratan Sulfates................ James L . Funderburgh Introduction: Keratan Sulfate Renaissance ......................... Keratan Sulfate Structure and Distribution ........................ Corneal KS .......................................................... Non-corneal KSI .................................................... KSII .................................................................. KSIII ................................................................. Keratan Sulfate Proteoglycans ...................................... SLRPs ................................................................ Aggrecan ............................................................. Cell-Associated KS .................................................. Brain ................................................................. Enzymatic Reactions of KS Biosynthesis ........................... Metabolic Control of KS Synthesis ................................. Acknowledgments ................................................... References ...........................................................
407
The Biosynthesis of GPI Anchors .................................... Yasu S. Morita, Alvaro Acosta.Serrano. and Paul T. Englund Introduction ......................................................... Structure of GPI Anchors ........................................... Glycan Core Modifications .........................................
417
407 407 408 409 409 410 410 410 411 411 412 412 413 414 414
417 417 417
Contents XXXIX 25.2.2 25.3 25.3.1 25.3.2 25.3.3 25.3.4 25.3.5 25.3.6 25.3.7 25.3.8 25.4 25.4.1 25.4.2 25.4.3 25.5 25.6
Variations in Anchor Lipid Structure ............................... GPl Precursor Synthesis ............................................. GlcNAc-PI Synthesis ................................................ GlcNAc-PI Deacetylation ........................................... Inositol Acylation .................................................... GPI Mannosylation .................................................. Transfer of EtN-P ................................................... Lipid Remodeling.................................................... Addition of Carbohydrate Side Chains ............................. Topology of Biosynthetic Pathways ................................. Attachment of the GPI Precursor to a Protein ..................... Basic Features ....................................................... Protein Machinery for GPI Addition ............................... Signal Sequence for GPI Addition. ................................. Evolution of GPI Biosynthesis ...................................... Future Studies ....................................................... Acknowledgments ................................................... References............................................................
419 419 420 421 421 422 423 423 424 424 425 425 426 426 426 427 427 427
26
435
26.1 26.2 26.3 26.3.1 26.3.2 26.3.3 26.3.4 26.3.5 26.3.6 26.4 26.5
Escherichiu coli Lipid A: A Potent Activator of Innate Immunity ... Teresa A . Garrett and Christian R . H . Raetz Introduction .......................................................... Structure of Lipopolysaccharide..................................... Lipid A Biosynthesis in E. coli ...................................... Acylation of UDP-GlcNAc ......................................... Disaccharide Formation ............................................. Phosphorylation by the Lipid A 4' Kinase .......................... Kdo Addition and the Late Acyltransferases ....................... Other Acyltransferases............................................... Transport of Lipid A and the Role of MsbA ....................... Lipid A Activation of Signal Transduction in Animal Cells ....... Summary ............................................................. Acknowledgments ................................................... References............................................................
435 435 437 439 440 440 441 442 442 444 447 447 447
11
Glycosidases ...........................................................
453
27
Lysosomal Degradation of Glycolipids............................... 455 Thomas Kolter and Konrad Sandhof Summary ............................................................. 455 Introduction .......................................................... 455 Mechanisms of Lysosonial Glycolipid Degradation ................ 456 Glycosidases ......................................................... 456
27.1 27.2 27.3 27.3.1
XL 27.3.2 27.3.3 27.3.4 27.3.5 27.3.6 27.4 27.4.1 27.4.2 27.4.3 27.4.4 27.4.5 27.4.6 27.4.7 27.5 27.5.1 27.5.2 27.6
28 28.1 28.2 28.3 28.4 28.4.1 28.4.2 28.4.3 28.5
28.5.1 28.5.2 28.5.3 28.6
29 29.1 29.2
Contents Topology of Endocytosis and Lysosomal Glycolipid Degradation Sphingolipid Activator Proteins ..................................... The GM2-activator and its role in lysosomal digestion ............ SAP-A to SAP-D .................................................... Lateral Pressure ...................................................... Lipid Composition .................................................. Membrane Curvature ............................................... Degradation of Selected Lipids ....... ........................... Ganglioside GM2 ................................................... Lactosylceramide .................................................... Glucosylceramide .................................................... Ceramide ............................................................. Sphingomyelin ....................................................... Sulfatide ............................................................. Galactosylceramide .................................................. Pathobiochemistry ................................................... Animal Models for Sphingolipidoses ............................... Therapy .............................................................. Future Directions .................................................... References ...........................................................
457 458 459 460 460 461 462 462 462 464 464 465 465 465 466 466 467 469 470 470
Lysosomal Degradation of Glycoproteins ........................... Nathan N . Aronson. Jr. Summary ............................................................. Introduction ......................................................... Roles of Lysosomes ................................................. Lysosomal Degradation of N-Linked Glycoproteins ............... General Features .................................................... Carbohydrate Digestion ............................................. Protein and Linkage Hydrolysis .................................... Formation of Thyroid Hormone via Lysosomal Degradation of Thyroglobulin ....................................................... Synthesis of Thyroid Hormone ..................................... Carbohydrate Degradation .......................................... Proteolysis ........................................................... Degradation of Free Polymannose-Type Oligosaccharides Derived from N-Linked Glycoproteins During Biosynthesis ................ References ...........................................................
473
Sialidases............................................................. Garry Taylor. Susan Crennell. Carl Thompson. and Marina Chuenkova Abstract .............................................................. Introduction .........................................................
473 473 474 475 475 476 476 477 477 478 479 479 481 485
485 485
Contents
XLI
29.3 29.4 29.5 29.6 29.7 29.8 29.9
Influenza Virus Neuraminidase ...................................... Paramyxovirus Hemagglutinin-Neuraminidase (HN) .............. Non-Viral Sialidases ................................................. Small Sialidases ...................................................... Large Sialidases ...................................................... T . cruzi Trans-Sialidase (TS) ........................................ Conclusion ........................................................... Acknowledgments ................................................... References ............................................................
486 487 487 490 491 491 493 494 494
30
Microbial Glycosidases............................................... Kenji Yamamoto. Su-Chen Li. and Yu-Teh L i Exo-Glycosidases .................................................... u-Glucosidase ........................................................ P-Glucosidase ........................................................ a-Galactosidase ...................................................... P-Galactosidase ...................................................... u.Mannosidase ....................................................... 0.Mannosidase ....................................................... P-N-Acetylhexosaminidase .......................................... u.N.Acetylga1actosaminidase ........................................ u-L-Fucosidase ....................................................... P.D.Fucosidase ....................................................... Sialidase .............................................................. KDNase .............................................................. u-L-Rhamnosidase ................................................... p-Xylosidase ......................................................... Endo.Glycosidases ...................................................
497
30.1 30.1.1 30.1.2 30.1.3 30.1.4 30.1.5 30.1.6 30.1.7 30.1.8 30.1.9 30.1.10 30.1.11 30.1.12 30.1.13 30.1.14 30.2 30.2.1 30.2.2 30.2.3 30.2.4 30.2.5 31
31.1 31.2 31.3 31.4 31.5 31.6 31.7 31.8
Endo.P.N.acetylg1ucosaminidase .................................... Peptide-N-glycanase F ............................................... Endo.u.N.acetylga1actosaminidase .................................. Endo-P-galactosidase ................................................ Endoglycoceramidase ................................................ References. ........................................................... Glycoprotein Processing Inhibitors ................................... Magid Osser and Alan D . Elbein Introduction ........................................................... Structural Classification ............................................. Distribution of Glycosidase Inhibitors in the Plant Kingdom ...... Isolation and Structural Determination ............................. Glycosidase Inhibitory Activity ..................................... Structure-Activity Relationships .................................... N-Linked Oligosaccharide Processing ............................... Inhibitors of N-Linked Oligosaccharide Processing.................
497 497 498 498 499 500 500 501 501 502 503 503 504 504 505 505 505 506 506 507 507 508 513 513 515 515 516 517 518 519 522
XLII 31.8.1 31.8.2 31.9
Contents Glucosidase Inhibitors ............................................... Mannosidase Inhibitors ............................................. Summary and Future Prospects ..................................... References ...........................................................
522 525 528 529
Index ...................................................................
11
Part I1
Biology of Saccharides
Vol. 4
Lectins and Saccharides Biology
Ill
Lectins ...............................................................
533
32
Plant Lectins ......................................................... Marilynn E. Etzler Summary ............................................................. Introduction ......................................................... Carbohydrate Specificity ............................................ Other Activities ...................................................... Structure ............................................................. Biological Roles ..................................................... Acknowledgments ................................................... References ...........................................................
535
32.1 32.2 32.3 32.4 32.5 32.6
33 33.1 33.2 33.3 33.4 33.5 33.6 33.7 33.8
34
34.1 34.2 34.3
Interactions of Oligosaccharides and Glycopeptides with Hepatic Carbohydrate Receptors ............................................. Yuan C. Lee and Reiko T. Lee Summary ............................................................. Introduction ......................................................... Molecular Characteristics of Hepatic Lectins ...................... Cellular Aspects of HL .............................................. Binding Specificity................................................... Photoaffinity Labeling ............................................... Subunit Organization on Rat Hepatocyte Surface ................. Applications ......................................................... References ........................................................... P-Type Lectins and Lysosomal Enzyme Trafficking ................ Patricia G. Marron-Teradu and Nancy M . Dahms Introduction ......................................................... Intracellular Trafficking of the MPRs .............................. Primary Structure and Biosynthesis of the MPRs ..................
535 535 536 539 540 543 546 547
549 549 550 551 552 553 557 558 559 560 563 563 564 566
Contents
XLIII
34.3.1 34.3.2 34.4 34.5 34.5.1 34.5.2 34.6
CI-MPR .............................................................. CD-MPR ............................................................. Lysosomal Enzyme Recognition by the MPRs ..................... Structural Determinants of Man-6-P Recognition .................. Expression of Mutant Forms of the MPRs ......................... Crystal Structure of the CD-MPR .................................. Conclusions .......................................................... Acknowledgments ................................................... References............................................................
35
The Siglec Family of I-Type Lectins ................................. 579 Paul R. Crocker and Soerye Kelm Introduction .......................................................... 579 The Immunoglobulin Superfamily and Carbohydrate Recognition 579 Siglecs as a Family of Sialic Acid Binding Proteins ................ 580 Biology of Siglecs .................................................... 581 Sialic Acids in Cellular Recognition ................................ 583 Mode of Carbohydrate Recognition by Siglecs ..................... 584 Importance of Multivalent Binding ................................. 588 Sialic Acid Recognition by the Immunoglobulin FoldEvolutionary Considerations ........................................ 588 Role of cis Interactions in Modulating Adhesion to Other Cells in trans ............................................................... 589 Sialoadhesin as a Macrophage Adhesion Molecule................. 590 Signalling Versus Adhesion Mediated by Siglecs ................... 591 Conclusions .......................................................... 592 Acknowledgments ................................................... 592 References............................................................ 592
35.1 35.2 35.3 35.4 35.5 35.6 35.7 35.8 35.9 35.10 35.11 35.12
36
36.1 36.2 36.2.1 36.2.2 36.3 36.3.1 36.3.2 36.3.3 36.3.4 36.3.5 36.3.6 36.3.7 36.4
C-Type Lectins and Collectins ....................................... Russell Wallis Summary ............................................................. Structure and Function of C-Type Animal Lectins ................. The Carbohydrate-Recognition Domain ............................ Ligand Binding ...................................................... Mannose-Binding Protein and Collectins ........................... Domain Organization ............................................... MBPs as Prototype Collectins ....................................... Ligand Binding by Serum MBP ..................................... MBP and Innate Immunity .......................................... Liver MBP ........................................................... Pulmonary Surfactant Proteins ...................................... Conglutinin and CL-43 .............................................. Conclusions ..........................................................
566 567 569 571 571 572 574 574 575
597 597 598 599 600 601 601 603 603 604 607 608 608 609
XLIV
Contents
Acknowledgments ................................................... References ...........................................................
609 609
Selectins .............................................................. Rodger P. McEver Introduction ......................................................... Structure of Selectins ................................................ Selectin Ligands ..................................................... Requirements for Selectins to Mediate Tethering and Rolling of Leukocytes under Hydrodynamic Flow ............................ Functions of Selectins and their Ligands in vivo ................... Conclusions .......................................................... References ...........................................................
613
Galectins ............................................................. Douglas N . W. Cooper and Samuel H . Barondes Introduction ......................................................... Galectin Structure ................................................... Novel Candidate Galectins .......................................... Unorthodox Subcellular Targeting .................................. Regulation of Galectin Expression .................................. Galectin Binding Specificity and Identified Ligands ................ Physiological Functions ............................................. Summary ............................................................. References ...........................................................
625 625 626 631 635 637 639 640 642 642
IV
Saccharide Biology ...................................................
649
39
Structures and Functions of Nuclear and Cytoplasmic Glycoproteins Robert S. Haltiwanger Introduction ......................................................... O-Linked N-Acetylglucosamine (0.GlcNAc) ....................... O-GlcNAc Appears to be a Regulatory Modification much like Phosphorylation ..................................................... Modulation of Protein Stability and Function by O-GlcNAc ..... Other Forms of Nuclear and Cytoplasmic Glycosylation .......... Unique Cytoplasmic Forms of Glycosylation ...................... Conventional Forms of Glycosylation in the Nucleus and Cytoplasm ........................................................... Nuclear and Cytoplasmic Lectins ................................... Conclusions .......................................................... Acknowledgments ................................................... References ...........................................................
65 1
37 37.1 37.2 37.3 37.4 37.5 37.6
38
38.1 38.2 38.3 38.4 38.5 38.6 38.7 38.8
39.1 39.2 39.2.1 39.2.2 39.3 39.3.1 39.3.2 39.3.3 39.4
613 613 614 619 621 621 622
651 652 653 655 658 658 660 661 662 662 662
Contents 40
40.1 40.2 40.3 40.3.1 40.3.2 40.3.3 40.4 40.5 40.6 40.7 40.7.1
40.7.2 40.7.3 40.7.4 40.7.5 40.8
41
41.1 41.2 41.3 41.3.1 41.3.2 41.3.3 41.3.4 41.3.5 41.4 41.4.1 41.4.2
XLV
Structure and Functions of Mucins .................................. 669 Joyce Taylor-Papadimitriou and Joy M . Burchell Classification of Mucins ............................................. 669 670 The Epithelial Mucins ............................................... Mucin Type O-Glycosylation Pathways ............................ 670 671 Initiation of O-Glycosylation ........................................ Chain Extension ..................................................... 671 Chain Termination ................................................... 671 Expression of Epithelial Mucins ..................................... 672 The Complex Gel-Forming Mucins: Processing and Function ..... 672 674 Epithelial Membrane Mucins ....................................... Studies Related to the MUCl Much ............................... 675 Changes in the Patterns of O-Glycosylation of MUCl in Breast 675 Cancer ................................................................ Differences in sites of glycosylation ................................. 675 Changes in the composition of O-glycans added to MUCl in 676 Breast Cancer ........................................................ Correlation in changes of Glycosyltransferase activities with changes in O-glycan structure in Breast Cancer .................... 676 Changes in Glycosylation of MUCl in other Cancers ............. 677 Effects of MUCl Expression on the Behavioral Properties of Cancer Cells.......................................................... 677 Effects on cell interactions and tumourogenicity .................... 677 678 MUCl Expression and Immune Responses ......................... Active Specific Immunotherapy Based on MUCl .................. 679 679 Animal models ....................................................... 680 Clinical studies ....................................................... Comments ............................................................ 681 References............................................................ 681 Biological Roles of Hyaluronan...................................... Bryan P . Toole Introduction .......................................................... Hyaluronan is a Biopolymer with Unusual Physical Properties .... Hyaluronan Binds to Several Types of Proteins (Hyaladherins) ... General Properties of Hyaladherins ................................. Structural Hyaluronan-Binding Proteins ............................ Hyaluronan Receptors ............................................... Intracellular Hyaluronan-Binding Proteins ......................... Inter-a-Trypsin Inhibitor ............................................ Hyaluronan-Dependent Pericellular Matrices Assemble Around Several Cell Types ................................................... Hyaluronan-Dependent Cellular “Coats” .......................... Assembly of Chondrocyte Pericellular Matrix ......................
685 685 685 687 687 688 688 689 689 690 690 691
XLVI 41.4.3 41.5 41.5.1 41.5.2 41.5.3 41.5.4 41.5.5 41.6
42 42.1 42.2 42.3 42.4 42.5 42.5.1 42.6 42.6.1 42.6.2 42.7 42.7.1 42.7.2 42.8 42.8.1 42.8.2 42.8.3 42.9 42.9.1 42.9.2 42.9.3 42.10
43 43.1 43.2
Contents
Tethering of Cell Surface Hyaluronan to Hyaluronan Synthase ... Hyaluronan Influences Cell Behavior During Morphogenesis and Tissue Remodeling .................................................. Migratory and Proliferating Cells are Surrounded by Hyaluronanenriched Matrices .................................................... Hydrated Pericellular Milieux Provide Cellular Pathways ......... Receptors Mediate Effects of Hyaluronan .......................... Hyaluronan-Cell Interactions in Limb Development ............... Hyaluronan-Cell Interactions in Other Physiological and Developmental Systems ............................................. Hyaluronan Plays a Crucial Role in Cancer ........................ References ...........................................................
691 693 693 693 693 694 695 696 696
Biological Roles of Heparan Sulfate Proteoglycans................. 701 Ofer Reizes. Pyong Woo Park. and Merton BernJeld Introduction ......................................................... 701 Heparan Sulfate Biosynthesis ....................................... 701 Functions of Heparan Sulfate ....................................... 702 703 Proteoglycans ........................................................ Intracellular Proteoglycans .......................................... 703 Serglycin and Heparin ............................................... 704 Cell Surface Heparan Sulfate Proteoglycans ........................ 705 Syndecans ............................................................ 705 Glypicans ............................................................ 706 Part-time Cell Surface Heparan Sulfate Proteoglycans ............. 707 Betaglycan ........................................................... 707 CD44 ................................................................. 708 Functions of Cell Surface Heparan Sulfate Proteoglycans ......... 708 Ligand Receptors .................................................... 708 709 Ligand Coreceptors .................................................. Shed Effectors ....................................................... 709 Extracellular Matrix Heparan Sulfate Proteoglycans and Their 710 Functions ............................................................ 710 Perlecan .............................................................. Agrin ................................................................. 712 Other Extracellular HSPGs ......................................... 713 713 Conclusions .......................................................... References ........................................................... 713 Biological Roles of Keratan Sulfate Proteoglycans.................. 717 Gary W. Conrad Introduction ......................................................... 717 718 Corneal Transparency ...............................................
Contents XLVII 43.3 43.4 43.5
Nerve Growth Cone Guidance ...................................... Cell Adhesion ........................................................ Other Possible Roles of KSPGs ..................................... Acknowledgment .................................................... References ............................................................
44
Developmental and Aging Changes of Chondroitin/Dermatan Sulfate Proteoglycans ........................................................ 729 J . Michael Sorrell. David A . Carrino. and Arnold I. Caplan Proteoglycans ........................................................ 729 Glycosaminoglycans ................................................. 729 Core Proteins ........................................................ 731 Hyalectans ........................................................... 731 Small Leucine-rich Proteoglycans ................................... 733 Chondrotin/Dennatan Sulfate Proteoglycans in Development and Aging ................................................................. 735 Core Proteins in Development. Aging. and Pathologies ............ 735 Chondroitin/Dermatan Sulfate Glycosaminoglycan Chains in Development. Aging. and Pathologies .............................. 736 Summary ............................................................. 740 References ............................................................ 740
44.1 44.2 44.3 44.3.1 44.3.2 44.4 44.4.1 44.4.2 44.5
45
45.1 45.2 45.3 45.4 45.5 45.6 45.7
46 46.1 46.2 46.3 46.4 46.5 46.6
719 721 722 723 723
Proteoglycans and Hyaluronan in Vascular Disease ................. Thomas N . Wight Introduction .......................................................... Proteoglycans and Hyaluronan ...................................... Versican (CSPGs) .................................................... Hyaluronan .......................................................... Decorin/Biglycan (DSPGs) .......................................... Perlecan/Syndecans (HSPGs)........................................ Summary ............................................................. Acknowledgments ................................................... References ............................................................
743
Functions of Glycosyl Phosphatidylinositols ......................... Nikola A . Baumann. Anant K. Menon. and David M . Rancour Introduction ........................................................... Parasite Coats: Extreme GPI-Anchoring ............................ Yeast GPIs and the Cell Wall ....................................... Paroxysmal Nocturnal Hemoglobinuria (PNH): Disease and Defects in GPI-Anchoring of Proteins .............................. GPIs in the Secretory and Endocytic Pathways ..................... Organization of GPI Proteins in the Plasma Membrane ...........
757
743 744 745 747 748 749 750 750 750
757 758 758 759 760 762
XLVIII
Contents
46.7 46.8 46.9 46.10 46.11
Association of GPI-Anchored Proteins with Caveolae ............. Detergent Insolubility and Signaling via GPI-Proteins ............. Membrane Release of GPI-Anchored Proteins ..................... GPIs as Second Messenger Signaling Molecules ................... Summary ............................................................. Acknowledgments ................................................... References ...........................................................
47
Glycosphingolipid Microdomains in Signal Transduction. Cancer. 771 and Development ..................................................... Sen-itiroh Hakomori and Kuzuko Handu Clustered GSLs as Functional Units ................................ 771 GSL Clusters. Associated with Signal Transducers. are Functional Units Separable from Caveolae ..................................... 772 Cell Adhesion Coupled with Signal Transduction Initiated by GSL Microdomain: Concept of Glycosignaling Domain (GSD) ........ 773 Role of GSLs in Control of Growth Factor and Hormone Receptors: Possible Relationship with GSL Microdomain ......... 774 Functional Role of Developmentally-Regulated and Tumor776 Associated GSLs ..................................................... References ........................................................... 778
47.1 47.2 47.3 47.4 47.5
48
48.1 48.2 48.3 48.3.1 48.3.2 48.4 48.5 48.6 48.7 48.8 48.9 48.10 48.10.1 48.10.2 48.10.3 48.10.4 48.11 48.12
The Primary Cell Walls of Higher Plants ........................... Jocelyn K. C. Rose, Mulcolm A . O’Neill, Peter Albersheim. and Alan Darvill Introduction (What is a Cell Wall?)................................. Purification of Cell Walls and Isolation of Wall Components ..... The Structural Components of the Primary Cell Wall ............. Cell Walls and the Diversity of Flowering Plants .................. The Structural Components of the Primary Wall .................. Biosynthesis of Wall Components .................................. Organization of the Plant Primary Cell Wall ....................... Cellulose-Xyloglucan Interactions .................................. Interactions Between Pectins and Other Cell Wall Components ... Glycoproteins in the Cell Wall ...................................... Heterogeneity in the Primary Cell Wall ............................ Function and Metabolism of Plant Primary Cell Walls ............ Mechanical Support ................................................. Regulation of Cell Expansion ....................................... Morphogenesis and Differentiation ................................. Plant Cell Wall Oligosaccharides in Defense and Cell Signalling .. Intercellular Transport and Storage ................................. Biotechnology and Future Directions in the Commercial Applications of Plant Primary Cell Walls ..........................
764 764 765 766 767 767 768
783 783 784 786 786 786 791 793 793 794 796 797 798 798 798 800 801 803 803
Contents
49
49.1 49.2 49.3 49.4 49.5 49.6
50
50.1 50.2 50.2.1 50.2.2 50.2.3 50.2.4 50.3 50.3.1 50.3.2 50.3.3
51
51.1 51.2 51.2.1 51.2.2 51.3 51.3.1 51.4
XLIX
Acknowledgment .................................................... References ............................................................
804 804
Glycolipids and Bacterial Pathogenesis .............................. ClifSord A . Lingwood Introduction .......................................................... Modulation of Glycolipid Receptor Function ...................... Stress Response and Glycolipid Receptors .......................... Subcellular Gb3 Trafficking ......................................... Model for Lipid Sorting Based on Chain Length ................... Glycosphingolipids and Signal Transduction ....................... Acknowledgments ................................................... References............................................................
809
Glycobiology of Viruses .............................................. Hildegard Geyer and Rudolf Geyer Summary ............................................................. General Aspects ...................................................... Functions of Viral Surface Glycoproteins ........................... Biosynthesis .......................................................... Function of Carbohydrate Substituents ............................. Oligosaccharide Diversity ........................................... Examples ............................................................. Friend Murine Leukemia Virus Complex ........................... Marburg Virus (MBGV) ............................................ Hepatitis B Virus (HBV) ............................................ Acknowledgments ................................................... References ............................................................
821
809 810 812 813 815 815 817 817
821 821 825 826 826 827 830 830 832 833 836 836
The Glycobiology of Influenza Viruses............................... 839 Stephen J. Stray and Gillian M . Air Introduction .......................................................... 839 Receptor Binding Proteins: Influenza A HAg and Influenza C HEF .................................................................. 840 Structure of Receptor Binding Domain and Mechanism of 843 Sialic Acid Recognition .............................................. HEF Esterase Domain and Mechanism of Cleavage ............... 844 844 Influenza NAm (types A and B) .................................... Mechanism of Sialic Acid Cleavage ................................. 845 Function of Viral Receptor Destroying Enzymes ................... 847 847 Acknowledgments ................................................... 848 References............................................................
L 52
52.1 52.2 52.3 52.4 52.5 52.6 52.7 52.7.1 52.7.2 52.7.3 52.7.4 52.7.5 52.8 52.9
53
53.1 53.2 53.3 53.3.1 53.3.2 53.3.3 53.4 53.4.1 53.4.2 53.4.3 53.4.4 53.4.5 53.4.6 53.4.7 53.5 53.6
Contents Glycobiology of Aids ................................................. Ten Feizi Abstract .............................................................. Introduction ......................................................... The Repertoire of N-Glycans on the Envelope Glycoprotein of HIV of Human Immunodeficiency Virus Produced in Different Cell Types............................................................ Evidence for the Occurrence of O-Glycans on the Envelope Glycoproteins of HIV-1 Produced in Certain Cell Lines ........... Oligosaccharides of gp 120 and gp 41 at N-Glycosylation Sites and Their Possible Influence on Viral Infectivity ................... gp 120 Glycosylation Can Influence Antigenicity and .. Immunogenicity ..................................................... Saccharides Recognized by Carbohydrate-binding Proteins and Antibodies as Potential Neutralization Epitopes on the Envelope Glycoprotein of HIV-1 .............................................. Lectins and Antibodies with Mannose-related Specificities ........ Antibodies to O-Glycan Sequences ................................. Antibodies to Blood Group A ...................................... Xeno-antibodies to Gala1-3Gal Sequence .......................... Potential Medical Relevance ........................................ Does Viral Oligosaccharide Display Influence Tissue Tropism? ... Concluding Remarks ................................................ Acknowledgment .................................................... References ...........................................................
851
Glycobiology of Protozoan and Helminthic Parasites ............... Richard D . Cummings. and A . Kwame Nyame Introduction ......................................................... General Classification of Parasites .................................. The Major Protozoan Parasites ..................................... Malaria .............................................................. . . ..................................................... Trypanosomiasis Leishmaniasis........................................................ Other Protozoan Parasites........................................... Entamoeba histolytica ............................................... Acanthamoeba ....................................................... Giardia lumblia ...................................................... Cryotosporidium parvum ............................................. Sarcocystis spp ....................................................... Toxoplusmu gondii., ................................................. Pneumocystis carinii ................................................. Helminthic Parasites ................................................. Carbohydrate-Binding Proteins in Parasitic Helminths ............
867
851 851 853 854 855 856 857 857 858 858 859 859 860 862 862 863
867 867 868 868 873 874 878 818 878 878 878 879 879 879 879 883
Contents 53.7 53.8
Unusual Glycans in Other Helminthic Parasites .................... Future Directions .................................................... Acknowledgments ................................................... References ............................................................
54
The Involvement of the Oligosaccharide Chains of Glycoproteins in Gamete Interactions at Fertilization ................................. Noritaka Hirohashi and William J . Lennarz Introduction .......................................................... Advantages of Marine Invertebrates as an Experimental System . . Induction of the Acrosome Reaction ................................ Studies in Sea Urchins ............................................... Studies in Starfish .................................................... Sperm-Egg Coat Binding ........................................... Studies in Mammals ................................................. Studies in Frog ....................................................... Studies in Ascidians .................................................. Studies in Sea Urchins ......... ................................... Carbohydrate as a Species-Specific Determinant ................... References ............................................................
54.1 54.2 54.3 54.3.1 54.3.2 54.4 54.4.1 54.4.2 54.4.3 54.4.4 54.5
55
55.1 55.2 55.3 55.4 55.4.1 55.4.2 55.5 55.6 55.6.1 55.6.2 55.6.3 55.7
56
56.1 56.2 56.3
LI 883 885 885 886
895 895 895 896 896 899 899 900 900 902 904 906 907
Glycosylation and Development ...................................... 909 Michde Aubery and Christian Derappe Summary ............................................................. 909 Introduction .......................................................... 911 Lectins as Tools to Analyze Changes in Cell-surface 911 Glycoconjugates During Development .............................. Cell-adhesion Molecules ............................................. 912 Neural Cell-adhesion Molecule ...................................... 912 The Adhesion Molecule L1 .......................................... 914 Glycosyltransferases ................................................. 914 Altered Expression of Endogenous Lectins During Development . 915 Galectins ............................................................. 915 Selectins .............................................................. 917 Other Endogenous Lectins .......................................... 917 Conclusion ........................................................... 918 References ............................................................ 918 Protein Glycosylation and Cancer ................................... James W. Dennis and Maria Granovskjj Introduction .......................................................... Protein Glycosylation Generates Molecular Diversity .............. Cancer Initiation and Progression ...................................
923 923 923 926
LII
Contents
56.4 56.5 56.6 56.7 56.8 56.9
Tumor Cell Proliferation ............................................ Cell Migration ....................................................... Sialylation and Metastasis........................................... Endogenous Lectins and Tumor Cell Adhesion .................... Carbohydrate Processing Inhibitors as Anti-Cancer Agents ....... Other Considerations ................................................ Acknowledgments ................................................... References ...........................................................
927 930 933 934 935 936 937 937
57
Lysosomal Storage Diseases ......................................... Nathan N . Aronson. Jr. Summary............................................................. Introduction ......................................................... Animal Models ...................................................... Mucopolysaccharidoses ............................................. Cathepsin K Deficiency and Pycnodysostosis ...................... Mouse Models for Tay-Sachs and Sandhoff Diseases .............. Impact of Lysosomal Diseases and Their Study .................... References ...........................................................
945
Genetic Diseases of Glycosylation ................................... Tomoya Akama and Michiko N . Fukuda Introduction ......................................................... CDGS ................................................................ CDGS Type I ........................................................ CDGS Type I1 ....................................................... HEMPAS ............................................................ References ...........................................................
959
57.1 57.2 57.3 57.4 57.5 57.6 57.7
58
58.1 58.2 58.2.1 58.2.2 58.3
59
59.1 59.2 59.3 59.3.1 59.3.2 59.3.3 59.3.4 59.3.5 59.3.6 59.4 59.5
Glycobiology of Helicobacter pylori and Gastric Disease ........... Karl-Anders Karlsson Introduction ......................................................... The Bacterial Surface and Molecular Mimicry ..................... Host Surfaces and H . pylori Recognition of Glycoconjugates: Unique Complexity.................................................. Sialic Acid ........................................................... Sulfatide ............................................................. Heparan Sulfate ..................................................... Fucose-Dependent Binding (H-1 and Lewis b) ..................... Gangliotetraosylceramide ........................................... Lactosylceramide .................................................... The Meaning of Multiple Binding Specificities ..................... Aspects for the Future ............................................... References ...........................................................
945 946 947 947 949 951 953 954
959 959 959 961 963 964 967 967 968 968 969 970 970 971 971 972 972 973 973
Contents
60 60.1 60.2 60.3 60.4 60.5 60.6 60.7 60.7.1 60.7.2 60.8 60.9 60.10 60.1 1 60.12 60.13 60.14 60.15
61
61.1 61.2 61.3 61.4 61.5
62 62.1 62.2 62.3 62.3.1
LIII
Immunoglobulin G Glycosylation and Galactosyltransferase Changes in Rheumatoid Arthritis .................................... 977 John S. Axford Introduction .......................................................... 977 977 Oligosaccharide Synthesis ........................................... Galactosyltransferase ................................................ 978 978 Immunoglobulin G .................................................. Rheumatoid Arthritis ................................................ 979 979 Quantification of IgG sugars in RAr ................................ RAr and Pregnancy .................................................. 980 980 Galactosylation of IgG .............................................. a3-Fucosylation of a1-Acid Glycoprotein .......................... 981 Agalactosyl-IgG and Rheumatoid Factor Binding ................. 982 Tissue-specific Galactosyltransferase Abnormalities in an Experimental Model of Rheumatoid Arthritis ...................... 983 Glycosylation Homeostasis within RAr Lymphocytes is Abnormal ............................................................ 985 Are the Rheumatoid Arthritis Associated Glycosylation Abnormalities Unique? .............................................. 986 Sugar Printing Rheumatic Disease is Possible ...................... 990 Rapid Profiling of IgG N-Glycans by Fluorophore-coupled Oligosaccharide Electrophoresis has the Potential of Differentiating 992 Rheumatic Diseases.................................................. In What Way could GTase Enzymatic Control be Abnormal? . . . . 992 Conclusion ........................................................... 993 References ............................................................ 994
Calnexin. Calreticulin and Glycoprotein Folding Within the Endoplasmic Reticulum .............................................. 997 Michael R. Leach and David B. Williams Structure and Properties of Calnexin and Calreticulin ............. 997 1000 Biological Functions ............................................... Mechanism of Action .............................................. 1002 Functional Relationship Between Calnexin and Calreticulin ..... 1005 Relationship with other ER Chaperones and Folding Catalysts . 1007 1008 References .......................................................... Glycobiology of The Nervous System .............................. Ronald L . Schnaar Introduction ........................................................ Nervous System Glycoconjugates-Overview .................... Nervous System Glycolipids ....................................... Galactosylceramides ...............................................
1013 1013 1013 1014 1014
LIV
Contents
62.3.2 62.4 62.4.1 62.4.2 62.5 62.6 62.6.1 62.6.2 62.7
Gangliosides and Related Anionic Glycosphingolipids ........... Nervous System Glycoproteins ..................................... Polysialic Acid ...................................................... The HNK-I Determinant .......................................... Nervous System Glycosaminoglycans ............................. Lectins in the Brain ................................................. Myelin-Associated Glycoprotein ................................... Other Nervous System Lectins ..................................... Concluding Remarks ............................................... References ..........................................................
1016 1019 1020 1020 1020 1021 1021 1022 1023 1023
63
Glycobiology of the Immune System ............................... Elizabeth F. Hounsell Infection and Pathogenesis ......................................... Control of the Immune Response .................................. Bacterial and Tumor Antigens. Mucins and Mucin-like Molecules ........................................................... Immunoglobulins and Pathology .................................. References ..........................................................
1029
63.1 63.2 63.3 63.4
64
64.1 64.2 64.2.1 64.2.2 64.2.3 64.3 64.3.1
64.3.2
Metabolic Engineering Glycosylation: Biotechnology’s Challenge to the Glycobiologist in the Next Millennium ...................... Thomas G. Warner Introduction ........................................................ Recent Developments in Carbohydrate Biosynthesis.............. Optimizing Sialylation of Recombinant Proteins by Metabolic Engineering Sialic Acid Biosynthesis............................... Optimizing Galactosylation of Recombinant Proteins by Metabolically Engineering Galactose Biosynthesis ................ Mannose Biosynthesis and Mannosylation of Recombinant Proteins ............................................................. Glycosylation Engineering Alternate Expression Hosts For Recombinant Protein Therapeutic Production .................... Engineering Glycosylation of Recombinant Proteins Expressed in Baculovirus-Insect Cells ......................................... Genes needed to supplement glycosylation of recombinant proteins in insect cells .............................................. Deleterious genes may need to be deleted or inhibited to enhance recombinant glycoprotein biosynthesis in insect cells.............. Engineering Glycosylation of Recombinant Proteins Expressed in Plants ............................................................. Genetic addition and supplementation needed to improve plant recombinant protein glycosylation ................................. Inhibition or deletion of plant glycosylation genes ................
1029 1033 1034 1036 1038
1043 1043 1044 1044 1049 1052 1053 1053 1054 1054 1056 1058 1059
Contents
64.4
Summary ........................................................... Acknowledgments ................................................. References ..........................................................
Index ...................................................................
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1059 1060 1060 11
List of Contributors (only main authors are listed)
Gillian Air Dept. of Biochemistry and Molecular Biology University of Oklahoma, Health Center BMSB 840, P. 0. Box 26901 Oklahoma City, OK 73190 USA Nathan N . Aronson Department of Biochemistry University of South Alabama MSB 2152 Mobile, AL 36688 USA Michele Aubery Ul80-INSERM U180 45 Rue Des Saints Peres 75006 Paris France Claudine Auge Laboratoire de Chimie Organique Multifonctionelle DR2 CNRS 462 Universite de Paris-Sud Inst. de Chimie Moleculaire (ICMO) 91405 Orsay Cedex France John S. Axford St. George’s Hospital Med. Ctr. Cranmer Terrace London SW17 ORE England
Samuel H. Barondes Langley Porter Psych. Inst. 401 Parnassus Avenue San Francisco, CA 94143-0984 USA Subhash Basu University of Notre Dame Stephan Chemistry Hall, Rm 443 Notre Dame, IN 46556 USA Jean-Marie Beau Univ. Paris-Sud Lab. de Synthese de Biomolecules URA CNRS 462, Inst. de Chimie 91405 Orsay France Merton Bernfield Harvard Medical School Enders Building, Room 961 300 Longwood Avenue Boston, MA 021 15 USA Mikael Bols Department of Organic Chemistry Aarhus University Langelandsgade 140 8000 Aarhus C Denmark
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List of Contributors
Inka Brockhausen Department of Medicine Queen’s University Etherington Hall, room 1021 Kingston, Ontario K7L 3N6 Canada Max Burger Friedrich Miescher Institut 4002 Basel Switzerland Arnold I. Caplan Case-Western Reserve University Cleveland, OH 44106 USA Henrik Clausen Department of Oral Diagnostics University of Copenhagen Norre Alle 20 DK-2200 Copenhagen N. Denmark Gary W. Conrad Kansas State University Ackert Hall Manhattan, KS 55606 USA Paul Crocker Department of Biochemistry The Welcome Trust Building University of Dundee Dundee, DDl 5HN Scotland Richard D. Cummings Department of Biochemistry and Molecular Genetics University of Oklahoma HSC 975 NE lofhSt., BRC 417 Oklahoma, OK 73104 USA Nancy Dahms Medical College of Wisconsin P. 0. Box 26509 8701 Watertown Plank Road Milwaukee, WI 53226-0509 USA Samuel J. Danishefsky Department of Chemistry Columbia University Havemeyer Hall
New York, NY 10027 and Laboratory for Bioorganic Chemistry The Sloan-Kettering Institute for Cancer Research 1275 York Avenue New York, NY 10021 USA Alan Darvill University of Georgia 220 Riverbend Road Athens, GA 30602 USA James W. Dennis Div. of Cancer and Cell Biology Mount Sinai Hosp., Res. Inst. 600 University Ave. Toronto, ON M5G 1x5 Canada Anne Dell Wolfson Laboratories Department of Biochemistry Imperial College of Science London SW7 2AY England Hugues Driguez CERMAV-CNRS B. P. 53 38041 Grenoble cedex France Dirk H. van den Eijnden Department of Medicinal Chemistry Vrije Universiteit Van der Boechorststraat 7 1081 BT Amsterdam The Netherlands Alan D. Elbein Dep. of Biochemistry and Molecular Biology University of Arkansas, Slot 516 4301 W. Markham Street Little Rock, AR 72205-7199 USA Paul Englund Johns Hopkins University School of Medicine 725 North Wolfe St. Baltimore, MD 21205 USA
List of Contributors Beat Ernst Institute of Molecular Pharmacy Pharmacenter Universitat Basel Klingenbergstrasse 50 4051 Basel Switzerland Mail:
[email protected] Marilynn E. Etzler University of California Davis, CA 95616 USA Ten Feizi Clinical Research Centre Watford Road Harrow, MDX HA1 3UJ England Bert Fraser-Reid Natural Products and Glycotechnology Research Institute Inc. 41 18 Swarthmore Road Durham, North Carolina 27707 USA Hudson H. Freeze The Burnham Institute 10901 N. Torrey Pines Road La Jolla, CA 92093 USA Michiko Fukuda Burnham Institute (formerly La Jolla Cancer Res. Fndm.) 10901 North Torrey Pines Road La Jolla, CA 92037 USA James L. Funderburgh Kansas State University Ackert Hall Manhattan, KS 66506 USA Robert M. Garbaccio Laboratory for Bioorganic Chemistry The Sloan-Kettering Institute for Cancer Research 1275 York Avenue New York, NY 10021 USA
Teresa Garrett Duke University Medical Center c/o Dr. C. Raetz P. 0. Box 3711 Durham, N C 27710 England Rita Gerardy-Schahn Institut fur Medizinische Mikrobiologie Medizinische Hochschule Hannover Carl-Neuberg-Strak 1 30625 Hannover Germany Roberto A. Geremia Centre de Recherches sur les M acromolkcules Vegttales Universite Joseph Fourier Cermav-CNRS, BP 53 38041 Grenoble Cedex 9 France Rudolph Geyer Biochemisches Institut Universitat Giessen Friedrichstr. 24 35392 Giessen Germany Gary R. Gray Department of Chemistry Institute of Technology University of Minnesota 207 Pleasant Street S. E. Minneapolis, MN 55455-0431 USA Sen-Itiroh Hakomori Pacific Northwest Research Foundation 720 Broadway Seattle, WA 98122 USA Robert S. Haltiwanger State University of New York Stony Brook, NY 11794-5215 USA Gerald W. Hart Department of Biological Chemistry John Hopkins University 401 Hunterian Building 725 N. Wolfe Street Baltimore, M D 21205-2185 USA
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LX
List of Contributors
Steve W. Homans School of Biochemistry and Molecular Biology University of Yeeds LSZ 9ST United Kingdom
Horst Kunz Institut fur Organische Chemie Universitat Mainz J.-Joachim-Becher-Weg 18-20 55099 Mainz Germany
Hideharu Ishida Department of Applied Bio-organic Chemistry Gifu University Gifu 501-11 Japan
Joseph T. Y. Lau Roswell Park Memorial Institute 666 Elm Street Buffalo, NY 14263 USA
Wolfgang Jager Biacore AB Jechtinger Strasse 8 79 111 Freiburg Germany Osamu Kanie Glycoscience Laboratory Mitsubishi Kasei Institute of Life Sciences (MILS) Machida-shi Tokyo 194-8511 Japan Karl-Anders Karlsson Institute of Medical Biochemistry G~teborgUniversity Medicinaraegatan 9A P. 0. Box 440 405 30 Gateborg Sweden Makoto Kiso Department of Applied Bio-organic Chemistry Gifu University Gifu, 50 1-11 Japan Sharon S. Krag Department of Biochemistry Johns Hopkins University 615 North Wolfe Street Baltimore, MD 21205 USA J. J. Krepinsky Department of Medical Genetics and Microbiology University of Toronto Toronto, ON M5S 1A8 Canada
Torvard C. Laurent Department of Medical and Physiological Chemistry University of Uppsala Avd. for Med. Kemi, Box 575 751 23 Uppsala Sweden Yuan C. Lee Department of Biology Johns Hopkins University 3400 North Charles Street Baltimore, MD 21218 USA Ludwig Lehle Lehrstuhl fur Zellbiologie und Pflanzenphysiologie Universitat Regensburg 93040 Regensburg Germany William J. Lennarz Department of Biochemistry and Cell Biology SUNY Stony Brook Room 450, Life Sciences Bldg. Stony Brook, NY 11794-5215 USA Steven V. Ley Chemical Laboratory University of Cambridge Lensfield Road Cambridge CB2 1EW England Yu-Teh Li Department of Biochemistry, SL43 Tulane University School of Medicine 1430 Tulane Avenue New Orleans, LA 701 12 USA
List of Contributors Ulf Lindahl Medical and Physiological Chemistry Uppsala Universitet P. 0. Box 575 75 12 Uppsala Sweden
Kelly L. Moremen Complex Carbohydrate Research Center University of Georgia 220 River Bend Road Athens, GA 30602-7229 USA
Clifford A. Lingwood Department of Microbiology Hospital for Sick Children 555 University Avenue Toronto, OT M5G 1x8 Canada
Heinz E. Moser GeneSoft Inc Two Corporate Drive South San Francisco, CA 9080 USA
Jean-Maurice Mallet Department de Chimie, URA 1686 Ecole Normale Superieure 24 rue Lhormond 75231 Paris Cedex 05 France Ernesto Marques Department of Pharmacology and MoleculaI Science John Hopkins University School of Medicine 725 North Wolfe Street Baltimore, M D 21205-2185 USA Jamey Marth Howard Hughes Medical Institute University of California, San Diego 9500 Gillman Drive, 0625 La Jolla, CA 92093-0625 USA Rodger McEver Oklahoma Medical Research Ed. 825 NE 13'h Street Oklahoma City, OK 73 104 USA Anant K. Menon Department of Biochemistry University of Wisconsin-Madison 420 Henry Mall Madison, WI 53706-1569 USA
LXI
Reinhold Ohrlein Ciba Speciality Chemicals Inc. K-420.2.19 4002 Base1 Switzerland Peter Orlean 309 Roger A d a m Laboratory University of Illinois at Urbana 600 South Mathews Avenue Urbana, IL 61801 USA Stefan Oscarson Department of Organic Chemistry Stockholm University Arrhenius Laboratory Svante Arrhenius vag 12 10691 Stockholm Sweden Monica M. Palcic Department of Chemistry University of Alberta Edmonton, AB, T6G 2G2 Canada Luigi Panza Dipartimento di Chimica Organica e Industriale Via Venezian 2 1 20133 Milano Italy Armando J. Parodi Biquimicas-Fundaction Campomar University of Buenos Aires Antonio Machado 151 Buenos Aires, 1405 Argentina
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List of Contributors
Serge Perez Centre de Recherches sur les MacromolCcules Vegetales UniversitC Joseph Fourier Cermav-CNRS, BP 53 38041 Grenoble Cedex 9 France
Konrad Sandhoff Institut fur Organische Chemie und Biochemie Universitat Bonn Gerhard-Domagk-Str. 1 53121 Bonn Germany
Thomas Peters Medizinische Universitat Zu Lubeck Institut fur Chemie Ratzeburger Allee 160 23538 Lubeck Germany
Harry Schachter Department of Biochemistry Hospital for Sick Children 555 University Avenue Toronto, ON M5G 1x8 Canada
Vince Pozsgay National Institute of Health 6 Center Dr. MSC 2720 Bldg. 6, Rm. 2A02 Bethesda, MD 20892-2720 USA
Roland Schauer Christian-Albrechts Universitat zu Kiel Olshausenstr. 40 24098 Kiel Germany
Christian Raetz Department of Biochemistry Duke University Medical Center P.O. Box 371 1 Durham, NC 27710 USA
Ronald L. Schnaar Department of Pharmacology and Molecular Science Johns Hopkins School of Medicine 725 North Wolfe Street Baltimore, MD 21205 USA
Ossi Renkonen University of Helsinki Institute of Biotechnology P. 0. Box 56 00014 University of Helsinki Finland
Richard R. Schmidt Fakultat fur Chemie Universitat Konstanz Postf. 5560 M 125 78457 Konstanz Germany
Peter J. Roach Department of Biochemistry Indiana University School of Medicine 635 Barnhill Dr. Indianapolis, IN 46202-5122 USA
Joel Shaper Oncology Center Johns Hopkins Hospital 600 North Wolfe Street Baltimore, MD 21287 USA
Steven D. Rosen Department of Anatomy University of California, San Francisco Box 0452 San Francisco, CA 94143 USA
Pierre Sinay Departement de Chimie Ecole Normale Superieure 24 rue Lhomond 75231 Paris Cedex 50 France
List of Contributors Dorothe Spillmann Department of Medical Biochemistry and Microbiology University of Uppsala The Biomedical Centre P. 0. Box 575 751 23 Uppsala Sweden Robert C. Spiro Department of Biological Chemistry Haward Medical School J o s h Research Laboratory 1 J o s h Place Boston, MA 02215 USA Jun-ichi Tamura Faculty of Education Tottori University Tottori 680-0945 Japan Garry Taylor Department of Biology and Biochemistry University of Bath Calverton Down Bath, BA2 7AY England Joyce Taylor-Papadimitriou Epithelial Cell Biology Laboratory Imperial Cancer Research Fund 44 Lincoln's Inn Field London, WC2A 3PX England Bryan P. Toole Department of Anatomy Tufts University HSC 136 Harrison Avenue Boston, MA 021 11 USA Eric J. Toone Department of Chemistry Duke University Durham, NC 27708-0346 USA Andrea T. Vasella Laboratorium fur Organische Chemie Eidgenossische Technische Hochschule Universitatsstrasse 19 8092 Zurich Switzerland
LXIII
Alain Veyrieres Ecole Nationale Superieure de Chimie de Rennes Campus du Beaulieu Avenue du General Leclerc 35700 Rennes France Barbara Vertel Department of Cell Biology and Anatomy Chicago Medical School 3333 Green Bay Road North Chicago, IL 60064-3095 USA Johannes F. G. Vliegenhart Bijvoet Center for Biomolecular Research Utrecht University P. 0. Box 80075 3508 TB Utrecht The Netherlands David J. Vocadlo Department of Chemistry University of British Columbia Vancouver B.C. V6T 1Zl Canada Russell Wallis Department of Biochemistry Glycobiology Institute University of Oxford South Parks Road Oxford, OX1 3QU England Thomas Warner 541 Wellington Drive San Carlos, CA 94070 USA Hans Peter Wessel F. Hoffmann-La Roche AG Pharma Research Discovery Chemistry PRPV-D Building 15/110 4070 Basel Switzerland Thomas N. Wight Department of Pathology SM-30 University of Washington School of Medicine Seattle, WA 98 195 USA
LXIV
List of Contributors
David B. Williams Department of Biochemistry University of Toronto Toronto, ON M5S 1A8 Canada Lawrence J. Williams Laboratory for Bioorganic Chemistry The Sloan-Kettering Institute for Cancer Research 1275 York Avenue New York, NY 10021 USA
Stephen G. Withers Department of Chemistry University of British Columbia 2036 Main Mall Vancouver, B.C. V6T 1Zl Canada Chi-Huey Wong Department of Chemistry Scripps Research Institute 10550 N. Torrey Pines Road La Jolla, CA 92037 USA
Abbreviations Used in Volumes 1 and 2
a1,3-GalT a2,3-SialT a2,6-SialT aGalF aGlcF aMuNeuAc apNPFuc apNPGal apNPGalNAc apNPGlc apNPGlcNAc apNPMan apNPNeuAc
A aa Ac AcHmb ACP AF AFM AgOTf AGP 019.
All AllNAc Aloc APC APP APS APS
a 1,3-GaIactosyltransferase a2,3-Sialyltransferase a2,6-sialyltransferase a-Galactosyl fluoride a-Glucosyl fluoride 4-Methylumbelliferone a-D-N-acetylneuraminic acid para-Nitrophenyl a-L-fucopyranoside para-Nitrophenyl a-D-galactopyranoside para-Nitrophenyl 2-acetamido-2-deoxy-a-~-galactopyranoside para-Nitrophenyl a-D-glucopyranoside para-Nitrophenyl 2-acetamido-2-deoxy-a-~-glucopyranoside para-Nitrophenyl a-D-mannopyranoside para-Nitrophenyl-a-D-N-acetyheuraminic acid Angstrom amino acid acetyl
N-2-acetoxy-4-methoxybenzyl acyl carrier protein aggregation factor atomic force microscopy silver trifluoromethanesulfonate (silver triflate) arabinogalactan protein asparagine-linked glycosylation ally1 N-Acetylallosamine Ally loxycarbony1 antigen-presenting cell acute phase protein adenosine phosphosulfate ammonium persulfate
LXVI
Abbreviations Used in Volumes I and 2
AR ARIS ASGP-R Asialo-GM1 Asn Asn GT ASTF-GP j3 1,4-GalT PManF PMuGlc PMuGlcNAc PMuXyl PoNPGal PoNPGlc PpClPMan PPhGal PPhGlc ppNP2dGlc PpNPGal PpNPGalNAc PpNPGlc PpNPGlcNAc PpNPMan PPNPXYl PpOMePhGlc PVGal 9-BBN BDA BHK bFGF BLAST BM BMP Bn Boc BOP bP Bu BU4NSSTr Bz Bzl CAA CAM CAN
acrosome reaction acrosome reaction-inducing substance asialoglycoprotein receptor p-D-Gal( 1-3)-b-~-GalNAc(1-4)-P-D-Gal( 1-4)-P-~-Glc-O-Cer asparagine asparagine glucosyltransferase (GalG1cNAcMan)zManGlcNAcz Asn P 1,4-Galactosyltransferase P-Mannosyl fluoride 4-Methylumbelliferyl P-o-glucopyranoside 4-Methylumbelliferyl 2-acetamido-2-deoxy-~-~-glucopyranoside 4-Methylumbelliferyl P-D-xylopyranoside ortho-Nitrophenyl P-D-galactopyranoside ortho-Nitrophenyl P-D-glucopyranoside para-Chlorophenyl P-D-mannopyranoside Phenyl P-D-galactopyranoside Phenyl P-D-glucopyranoside para-Nitrophenyl2-deoxy-P-~-arabino-hexopyranoside para-Nitrophenyl P-D-galactopyranoside para-Nitrophenyl 2-acetamido-2-deoxy-P-~-galactopyranoside para-Nitrophenyl P-D-glucopyranoside para-Nitrophenyl 2-acetamido-2-deoxy-~-~-glucopyranoside para-Nitrophenyl P-D-mannopyranoside para-Nitrophenyl P-D-xylopyranoside para-Methoxyphenyl P-D-glucopyranoside Vinyl 0-D-galactopyranoside 9-Borabicyclo[3.3.llnonane butane diacetal baby hamster kidney basic fibroblast growth factor basic alignment search tool basement membrane bis(monoacylg1ycero)phosphate benzyl tert-butoxycarbonyl benzotriazol-1-yloxy-tris(dimethy1amino)phosphoniumhexafluorophosphate base pair butyl Tetrabutylammoniumsaltoltriphenylmethanethiol benzoyl benzyl carbohydrate amino acids cell adhesion molecule Cer(1V)ammoniumnitrate
Ahhreviutions Used in Volumes 1 and 2 LXVII CAT CBMIT CBS CBS Cbz CCCP CD CDA CDGS CDMT cDNA CDTA Cer CHO CgOse4 CGTase CI CI8 CIAP ClAc ClNP CMLN CMP CMP CMP-NeuAc/ CMP-NeuSAc CMP-Sia CNBr CNS CoA Coll CPG CRD
cs
CSA CSA
csc CSPG CST CTL CTP Da DAF DAG DBA DBMP
chloramphenicol acetyltransferase 1,l-carbonylbis(3-methylimidazolium triflate Gal(S03)Pl- 1Cer Cerebroside sulfate benzyloxycarbonyl carbonyl cyanide m-chlorophenylhydrazone cation dependent cyclohexane-l,2-diacetal carbohydrate-deficient glycoprotein syndrome 2-chloro-4,6-dimethoxy-l,3,5-triazine complementary DNA diaminocyclohexane tetraacetic acid ceramide Chinese hamster ovary fi-~-Gal( 1-3)-o-~-GalNAc( 1-4)-fi-~-Gal( 1-4)-p-~-Glc cyclodextrin glucosyltransferase cation independent Cycloisomalto-octaose calf intestine alkaline phosphatase [ EC.3.1.3.11 chloroacetyl 2-Chloro-4-nitrophenyl calf mesenteric lymph node cytosine monophosphate cytidine 5'-monophosphate cytidine 5'-monophosphate N-acetylneuraminic acid Cytidine 5'-monophosphate sialic acid cyanogen bromide central nervous system coenzyme A sym-collidine controlled pore glass carbohydrate-recognition domain chondroitin sulfate Campher sulfonic acid chondroitin-4-sulfate chondroitin-6-sulfate chondroitin sulfate proteoglycan castanospermine cytotoxic T cell 5 '-Cytidinetriphosphate Dalton decay accelerating factor diacylglucosamine ((strain D x strain B) x strain A) mice 2,6-di-tert-butyl-4-methylpyridine
LXVIII Abbreviations Used in Volumes 1 and 2 DBU DCC DCPhth Dde DDP DDQ DEPC DF 2dGlc DIBALH DiBz DIG DIM DIPEA DMA DMAP DME DMF DMJ DMM DMPU DMSO DMTST DMTST 2,4-DNP DNJ DNJ Do1 Dol-P Dol-PP DP DPPA DRM DS DTBMP DTBP DTBPI DTT E-CAD ECM EDCD/EDCI EDTA EGF eIF EM
1,8-diazabicyclo[5.4.01undec-7-ene N ,N’-Dicyclohexylcarbodiimide 4,s-dichlorophthaloyl N- 1- (4,4-dimethy1-2,6-dioxocyc1ohexy1idene) ethy 1 dialkyl N,N-diethylphosphoramidites 2,3-Dichloro-S,6-dicyano-1,4-benzoquinone diethylphosphoryl cyanide deactivation factor 2-Deoxy-arabino-hexose Diisobutylaluminumhydride Dibenzoyl detergent-insoluble glycolipid complex 1,4-dideoxy-1,4-imino-~-mannitol diisopropylethylamine N ,N-dimethylacetamide 4-Dimethylaminopyridine 1,Zdimethoxyethane N ,N-dimethylformamide 1-deoxymannojirimycin dimethylmaleoyl N ,N’-dimethylhexahydropyrimidin-2-one dimethyl sulfoxide dimethyl(methy1thio)sulfonium tetrafluoroborate (dimethyl (methy1thio)sulfoniumtriflate) Dimethyl(methy1thio)sulfoniumtetrafluoromethansulfonate 2,4-Dinitrophenyl deoxynojirimycin 1,5-Dideoxy-l,S-irnino-D-glucitol (deoxynojirimycin) dolichol dolichyl phosphate dolichyl pyrophosphate degree of polymerization diphenylphosphoryl azide detergent-resistant membrane dennatan sulfate 2,6-di-tert-butyl-4-methylpyridine 2,6-di-tert-butylpyridine 2,6-di-tert-butylpyridiniumiodide dithiothreitol Epithelial Cadherin I extracellular matrix 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide ethylene diamine tetraacetic acid epidermal growth factor eukaryotic initiation factor electron microscopy
Abbreviations Used in Volumes I and 2 LXIX endo H EPGase ER ER ESI EST EtN EtN-P F FAK FCOE FGF Fmoc/FMOC FSP FT FTIR FTIR Fuc Fuc FucT GA GAG Gal Gal GalNAc GalT Gal- 1-P UT Gb3 Gb;l GC GC-MS GDI, GDP GDP GDP-Fuc GDP-Man GDPMP Gg3 GI GI1 Glc Glc GlcA GlcN GlcN
endo-0-N-acetylglucosaminidase H endopolygalacturonase endoplasmic reticulum endoplasmic reticulum electrospry ionization expressed sequence tag ethanolamine ethanolamine phosphate fusion protein focal adhesion kinase fluorophore-coupled oligosaccharide electrophoresis fibroblast growth factor 9-Fluorenylmethoxylcarbonyl(fluorenyl-9-methoxycarbonyl) fucose sulfate polysaccharide a-(1-3/4)-fucosyltransferase [ EC.2.4.1.651 Fourrier transform infra red Fourier transform infra-red (spectroscopy) fucose/fucosyl fucose fucosyltransferase Golgi apparatus glycosaminoglycan galactose galactose/galactosy1 N-acetylgalactosamine galactosyltransferase Gal- 1-P-uridyltransferase Gala+4Gal~1+4Glc~lA+lCer
GalNAcPl+3Gala1+4Gal~l+4Glc~l+lCer glucosyl cerdmide gas chromatography-mass spectrometrya-DNeuAc(2-3)-P-~-Gal(1-3)-p-~-GalNAc(1-4)-[a-DNeuAc(2-3)]-P-~-Gal(1-4)-p-~-Glc-o-CerGDP guanosine diphosphate guanosine 5'-diphosphate guanosine 5I-diphosphate fucose guanosine 5'-diphosphate mannose GDP-Man pyrophosphorylase
GalNAcP1+4Galpl+4Glcpl+lCer gastro-intestinal glucosidase I1 glucose/glucosyl glucose glucuronic acid 2-Amino-2-deoxy -glucopyr anose glucosamine
LXX
Abbreviations Used in Volumes I and 2
GkN3 Glc3NAc GlcNAc GlcNAc GlcNAc, GlcNAc-Oxazoline GlcNPht GlcNTeoc Glucal GLUT GM~ GMi
GM3 GM3 GMP GnT GP GPI GRIFIN GRP GSL GT GT GTA GTB H HA HAF HAg HAS HBP HBPyU hCG HEMPAS test HeP HEPES HEV HIV HIV
2-Azido-2-deoxy-~-glucopyranose 3-Acetamido-3-deoxy-~-glucopyranose N-acetylglucosamine 3,4,6-tri-O-acetyl-N-acetylglucosamine { p-~-GlcNAc( 1-4)) ( , - l ) - ~ - G l ~ N A ~ 2-Methyl-4,5-dihydro-(1,2-dideoxy-a-~-g~ucopyranoso) [2,1-d]-1,3-oxazole 2-Deoxy-2-phthalimido-~-glucopyranose 2-Deoxy-2-aminot~ethoxylcarbonyl-~-g~ucopyranose 1,5-Anhydr0-2-deoxy-~-arabino-hex1-enitol glucose transporter GalPl+3GalNAcf31 -+[NeuAcu2+3]Gal~l+4Glc~l+1Cer p-D-Gal(1-3)-p-~-GalNAc(1-4)-[u-~-NeuAc(2-3)1-p-~Gal( 1-4)-p-D-GlC-O-Cer P-D-GalNAc(1-4)-[u-~-NeuAc(2-3)]-p-~-Gal( 1-4)-p-~Glc-0-Cer NeuAca2+3Gal~l-+4G1c~l+ lCer a-~-NeuAc(2-3)-P-D-Gal(1-4)-p-~-Glc-O-Cer guanosine monophosphate N-acetylglucosaminyltransferase glycoprotein glycosyl phosphatidylinositol galectin-related interfiber protein glycine-rich protein glycosphingolipid p-(1-4)-galactosyltransferase [ EC.2.4.1.221 (glycosyltransferase) UDP-G1c:glycoprotein glucosyltransferase human blood group A glycosyltransferase human blood group B glycosyltransferase Fucul+2Galpl+3/4GlcNAcP hyaluronic acid, hyaluronate Hulicondriu aggregation factor hemagglutinin hyaluronate synthesizing enzyme hexosamine biosynthetic pathway 0-(benzotriazole-1-yl)-N,N,N,N-bis(tetramethy1ene)uronium hexafluorophosphate human chorionic gonadotropin hereditary erythroblastic multinuclearity with a positive acidified-serum-lysis (congenital dyserythropoietic anemia type 11) heparin N-(2-Hydroxyethylpiperazine)-N'-(2-ethanesulfon~c acid) high endothelial venules Human immunodeficiency virus human immunodeficiency virus
Abbreviations Used in Volumes 1 and 2 HL HMG HN HOAll HOAT HOBt HOMO HPLC HPLC HRGP HS HSD HSPG HUS HYCRON HYP ICAM IDCP IDCT IduA IGF Ig IgSF IIDQ IL IPG IU IV3NeuAc PGalNAcGbOse4 I V NeuAcII NeuAcCgOse4 K
kb kDa Kdn
Kdn/KDN Kdo Kdo K-4 Ki KIF Krn KS KSPG
LXXI
hepatic lectin high mobility group (proteins) hemagglutinin-neuraminidase Ally1 alcohol 1-hydroxy-7-azabenztriazole 1-hydroxybenzotriazole hydrate highest occupied molecular orbital high-performance liquid chromatography high performance liquid chromatography hydroxyproline-rich glycoprotein heparan sulfate highly sulfated domain heparan sulfate proteoglycan hemolytic uremic syndrome hydroxycrotyl-oligoethylene glycol-n-alkanoyl 4-hydroxyproline intercellular adhesion molecule iodonium dicollidine perchlorate iodonium dicollidine triflate iduronic acid insulin-like growth factor immunoglobulin immunoglobulin superfamily of proteins isobutoxyisobutyldihydroquinoline interleukin inositol phosphoglycan international unit p-D-GalNAc(1-3)-p-~-GalNAc(1-3)-u-~-Gal(1-4)-p-DGal(1-4)-~-Glc a-u-NeuAc(2-3)-P-~-Gal(1-3)-p-~-GalNAc(1-4)-[a-DNeuAc(2-3)]-P-~-Gal(1-4)-Dkinase enzyme activity coefficient kilobase (thousand base pairs) kiloDalton 2-keto-3-deoxy-nononicacid, formally 5-desamino-5hydroxyneuraminic acid 3-deoxy-~-y~ycero-D-gu~ucto-2-nonulosonic acid ketodeoxoctulosonic acid (3-deoxy-~-mannooctulosonic acid) 2-keto-3-deoxy-~-manno-octulosonic acid kinase enzyme activity coefficient, at equilibrium kinase enzyme activity coefficient, for inhibition kifunensine kinase enzyme activity coefficient, for structural modification(s) keratan sulfate keratan sulfate proteoglycan
LXXII Abbreviations Used in Volumes 1 and 2 LacAm LacCer LacNAc LacNAc LAD LAMP LBP Lc3 LDA Lea Lea Leb Lea, LeX LeX LeX Ley Leu Lev LNP LPS LRP LRR LUMO LYS mAb MAd MAF MAG MALDI-TOF MALDI-TOF Man ManNAc MAP MASP Man-T MBL MBP MBz MCD MDBK MDCK ME MEM MHC MK
lactosamine GalP 1+4GlcP1+ 1Cer N-acetyllactosamine N-acetyllactosamine leucocyte adhesion deficiency lysosomal associated membrane protein lipopolysaccharide-binding protein GlcNAcPl-.3Gal~1+4GlcP1+ 1Cer Lithium diisoprypropylamide GalP 1+3[Fucal+4]GlcNAcP1+3Gal~1+GlcP P-~-Gal(l-3)-[a-~-Fuc( 1-4)]-~-GlcNAc Fuca 1+2GalP 1+3[ Fucal-+4]GlcNAc~ 1+3GalP 1-4GlcP Lewis a, Lewis x determinants p-D-Gal(1-4)-[a-~-Fuc( 1-3)]-~-GlcNAc GalP 1+4[ Fucal+3]GlcNAcP 1+3GalP 1-+4GlcP Fuca 1-2GalP 1+4[Fucal+3]GlcNAcP 1+3GalP 1-4ClcP leucine levulinoyl lectin and nucleotide phosphohydrolase lipopolysaccharaide lipoprotein receptor-related protein leucine-rich repeat (amino acid/protein) lowest unoccupied molecular orbital lysine monoclonal antibody mucosal addressin Microciona prolifera aggrigation factor myelin-associated glycoprotein mass-analyzed laser desorption ionization-time of flight matrix-assisted-laser desorption ionization time of flight mass spectrometry mannose N-acetylmannosamine microtubule-associated protein MBP-associated serine protease mannosyltransferase mannose-binding lectin mannose-binding protein p-methoxybenzoyl macular corneal dystrophy Madin-Darby bovine kidney (cells) Madin-Darby canine kidney (cells) methoxyethyl methoxyethoxymethyl major histocompatibility complex myokinase
Abbreviations Used in Volumes 1 and 2 LXXIII mol.wt. MP MPEG MPR MPS M, MS MSD MTr Mu MUC NA NAc nAChR NAm NANA N-BOC NBS NCAM NCS N DP NDP NDST NEM 3NeuAcCgOse4 Neu5Ac NeuAc NGF NIH NIS NK nLc4 Nle NMK NMP NMR NOE NPG NS NTP Nu OD (2-OH)-Lea (2-OH)-Le" (2-OH)-sLea
molecular weight p-methoxyphenyl polyethylene glycol monomethyl ether mannose 6-phosphate receptor mucopolysaccharidosis apparent molecular weight mass spectrometry multiple sulfatase deficiency, Austin disease p-methoxytrityl 4-Methylumbelliferone mucin N-acetylated disaccharide unit N-acetyl nicotinic acetylcholine receptor neuraminidase N-acetylneuraminic acid N-tert-butoxycarbonyl N-bromosuccinimide neural cell adhesion molecule N-chlorosuccinimide nucleoside diphosphates nucleoside-diphosphate N-deacetylaselN-sulfotransferase N-ethylmaleimide p-~-Gal(1-3)-o-~-GalNAc( 1-4)-[a-~-NeuAc(2-3)]-P-DGal( 1-4)-D-Glc N-acetylneuraminic acid N-acetylneuraminic acid nerve growth factor National Institutes of Health N-iodosuccinimide natur a1 killer Gal~l+4GlcNAc~1+3Gal~1-t4Glc~1-+ 1Cer Norleucin nucleoside monophosphate kinase nucleoside monophosphate nuclear magnetic resonance nuclear Overhauser effect n-pentenyl glycoside N-sulfated disaccharide unit nucleoside triphosphate nucleophile optical density P-D-Gal(1-3)-[a-~-Fuc( 1-4)I-D-Glc p-D-Gal(1-4)-[a-~-Fuc(1-3)I-D-Glc a-NeuAc(2-3)-P-~-Gal(1-3)-[a-~-Fuc(1-4)]-~-Glc
LXXIV Abbreviations Used in Volumes I and 2 (2-OH)-sLe” OR ORF OSP OST OST P PA Pac PAMP PAPS PAPS PARP PBL pClP PCR PDGF PDI PEG PEGA PEP PEP PfP
pmu
PG PGM PGM Ph PhSeOTf PhSOTf Phth PI Piv PK PMB pNP-a-Man PNS PNZ POEPOP Ppase ppGaNTases PPK PRP PSA PSGL
a-NeuAc(2-3)-P-~-Gal(1-4)-[a-~-Fuc( 1-3)]-~-Glc dimethyl(methy1thio)sulfonium trifluoromethanesulfonate open reading frame 0-specific polysaccharides oligosaccharyltransferase N-oligosaccharyltransferase phosphate 2-Aminopyridine phenacyl pathogen-associated molecular pattern) 3 ‘-phosphoadenosine 5’-phosphosulfate phosphoadenosine phosphosulfate procyclic acidic repetitive protein peripheral blood leucocytes para-Chlorophenyl polymerase chain reaction platelet-derived growth factor protein disulfide isomerase poly(ethy1ene glycol) polyethylene glycol N,N-dimethylacrylamide copolymer phospho(eno1)pyruvate phosphoenolpyruvate pentafluorophenyl N,N,N’,N’-bis(tetramethylene)-O-pentafluorophenyluronium hexafluorophosphate phosphatidylglycerol phosphoglucomutase phosphoglucomutase phenyl Phenylseleniumtriflate Phenylsulfoniumtriflate phthaloyl phosphatidylinositol pivaloyl pyruvate kinase p-methoxybenzyl p-nitropheny1-a-D-mannoside peripheral nervous system p-nitrobenzyloxycarbonyl poly oxyethylene-polyoxypropylene pyrophosphatase UDP-Ga1NAc:polypeptide N-acetylgalactosaminyltransferases polyphosphate kinase proline-rich protein polysialic acid P-Selectin glycoprotein ligand
Abbreuiutions Used in Volumes I and 2 LXXV PSGL-1 PSGL- 1 PTG PYr 9.Y. RA RAr RACE rER RHAMM ROESY RT-PCR SA SAP SAT SBA SBu SDS SDS-PAGE Se SE Ser SEt SGC SGG SGGL SGLT sia sLea sLea, sLe' sLe' 6'-SLN SLRP SMC SP SPh SPH SSEA ST ST3 ST6 STF-GP SV
sw
P-selectin glycoprotein ligand-1 P-selectin glycoprotein ligand-1 peptidoglycan pyridine quantitative yield retinoic acid rheumatoid arthritis rapic amplification of cDNA ends rough endoplasmic reticulum receptor for hyaluronan-mediated motility rotating-frame nuclear Overhauser effect reverse transcription polymerase chain reaction sialyl saposin sialyltransferase soybean agglutinin Thiobutyl sodium dodecyl sulfonate sodium dodecylsulfate-polyacrylamide gel electrophoresis secretor enzyme 2-(trimethylsily1)ethyl serine Thioethyl sulfogalactosyl ceramide sulfogalactosyl glycerolipid sulfoglucuronyl glycolipid sodium-glucose transporter sialic acid a-~-NeuAc(2-3)-P-~-Gal( 1-3)-[ a-~-Fuc( 1-4)]-~-GlcNAc(sialyl Lewisa trisaccharide) sialylated Lewis a, sialylated Lewis x determinants a-~-NeuAc(2-3)-P-~-Gal( 1-4)-[a-~-Fuc( 1-3)]-~-GlcNAc(sialyl Lewis' trisaccharide) 6'4alyl-LacNAc small leucine-rich proteoglycan sialomucin complex spacer Thiophenyl saccharide-peptide hybrids stage specific embryonic antigen sulfurotransferase recombinant rat liver a-(2-3)-sialyltransferase [EC.2.4.99.6] rat liver a-(2-6)-sialyltransferase jEC.2.4.99.11 (NeuAcGalGlcNAcMan)2ManGlcNAqAsn synaptic vesicle-associated protein swainsonine
LXXVI Abbreviations Used in Volumes 1 and 2 TATU TBAF TBAI TBDMS TBDMSOTf TBDPS TBDPSCl TBTU Bu TCA Tcoc TCP TCR TDS TEMED Teoc TES TESOTf Tf20 TFA TFDMSCl TfOH TGF TGN THF Thr tlc TM TMD TMS TMSCN TMSN3 TMSOTf to1 Tos t-PA TriBz Troc Trt Ts UDP UDP UDP-Gal UDP-Gal
0-(7-azabenzotriazol-1-yl)-3-tetramethyluronium tetrafluoroborate Tetrabutylammoniumfluoride Tetabutylammoniumiodide tert-butyldimethylsilyl tert-butyldimethylsilyl trifluoromethanesulfonate (tert-butyldimethylsilyl triflate) tert-butyldiphenylsilyl tert-butyldiphenylsilylchloride 0-(benzotriazol- 1-yl)-N,N,N',N'-tetrauroniumtetrafluoroborate tert-butyl trichloroacetyl trichloroethyloxycarbonyl tetrachlorophthaloyl T cell receptor thexyldimethylsilyl tetramethylethylenediamine 2,2,2-trichloroethoxycarbonyl triethylsilyl triethylsilyl trifluoromethanesulfonate (triethylsilyl triflate) trifluoromethane sulfonic acid anhydride trifluoroacetic acid trifluoromethyldimethylsilylchloride trifluoromethanesulfonic acid (triflic acid) transforming growth factor trans Golgi network tetrahydrofuran threonine thin layer chromatography transmembrane trans-membrane domain trimethylsilyl trimethylsilyl cyanide trimethylsilyl azide trimethylsilyl trifluoromethanesulfonate (trimethylsilyl triflate) toluene p-toluenesulfonyl (tosyl) tissue plasminogen activator factor tribenzoyl
2,2,2-trichloroethoxycarbonyl triphenylmethyl (trityl) p-toluenesulfonyl (tosyl) uridine 5'-diphosphate uranyl diphosphate UDP-a-D-galactose uridine 5'-diphosphate-galactose
Abbreviations Used in Volumes I and 2 UDPGE UDP-Glc UDPGP UMD UMP UTP
uv vc
VE VL VSG
vsv
VT vWF WBP XYl XY12 Z ZP
LXXVII
uridine 5'-diphosphate-glucose epimerase [EC.5.1.3.2.] uridine 5'-diphosphate-glucose UDP-Glc pyrophosphorylase unmodified domain uranyl monophosphate uranyl triphosphate ultraviolet vitelline coat vitelline envelope vitelline layer variant surface glycoprotein vasicular stomatis virus verotoxin von Willebrand factor wheat germ agglutinin binding protein xylose p-D-xyl(1--4)-D-xyl benzyloxycarbonyl zona pellucida
Abbreviations Used in Volumes 3 and 4
A" aa ACP AGP 4 7
APC APP APS AR ARIS ASGP-R Asn Asn GT BHK bFGF BLAST BM BMP bP CAM CAT CCCP CD CDGS CDTA Cer CHO CI CMLN CMP
Angstrom amino acid acyl carrier protein arabinogalactan protein asparagine-linked glycosylation antigen-presenting cell acute phase protein adenosine phosphosulfate acrosome reaction acrosome reaction-inducing substance asialoglycoprotein receptor asparagine asparagine glucosyltransferase baby hamster kidney basic fibroblast growth factor basic alignment search tool basement membrane bis(monoacy1glycero)phosphate base pair cell adhesion molecule chloramphenicol acetyltransferase carbonyl cyanide m-chlorophenylhydrazone cation dependent carbohydrate-deficient glycoprotein syndrome diaminocyclohexane tetraacetic acid ceramide Chinese hamster ovary cation independent calf mesenteric lymph node cytosine monophosphate
LVIII
Abbreviations Uscd in Volumes 3 and 4
CNS CoA CRD CS CSPG CST CTL Da DAF DAG DBA DIG DIM DMJ DMSO DNJ Do1 Dol-P Dol-PP DP DRM DS ECM EDTA EGF eIF EM endo H EPGase ER EST EtN EtN-P F FAK FCOE FGF FSP FTIR Fuc FucT GA GAG Gal GalNAc GalT
central nervous system coenzyme A carbohydrate-recognition domain chondroitin sulfate chondroitin sulfate proteoglycan castanospermine cytotoxic T cell Dalton decay accelerating factor diacylglucosamine ((strain D x strain B) x strain A) mice detergent-insoluble glycolipid complex 1,4-dideoxy-l,4-imino-~-mannitol 1-deoxymannojirimycin dimethyl sulfoxide deoxynojirimycin dolichol dolichyl phosphate dolichyl pyrophosphate degree of polymerization detergent-resistant membrane dermatan sulfate extracellular matrix ethylene diamine tetraacetic acid epidermal growth factor eukaryotic initiation factor electron microscopy endo-p-N-acetylglucosaminidaseH endopol y galacturonase endoplasmic reticulum expressed sequence tag ethanolamine ethanolamine phosphate fusion protein focal adhesion kinase fluorophore-coupled oligosaccharide electrophoresis fibroblast growth factor fucose sulfate polysaccharide Fourier transform infra-red (spectroscopy) fucose fucosyltransferase Golgi apparatus glycosaminoglycan galactose N-acetylgalactosamine galactosyltransferase
Ahbreniutions Used in Volumes 3 and 4
GC GC-MS GDP GI GI1 Glc GlcA GlcN GlcNAc GLUT GnT GP GPI GRIFIN GRP GSL GT GTA GTB HA H Ag HAS HBP HEMPAS hCG HeP HEV HIV HL HMG HN HPLC HRGP HS HSD HSPG HUS ICAM lduA IGF Ig IgSF IL IPG
1u
LIX
glucosyl ceramide gas chromatography-mass spectrometry guanosine diphosphate gastro-intestinal glucosidase I1 glucose glucuronic acid glucosamine N-acetylglucosamine glucose transporter N-acetylglucosaminy ltransferase glycoprotein glycosyl phosphatidylinositol galectin-related interfiber protein glycine-rich protein glycosphingolipid UDP-G1c:glycoprotein glucosyltransferase human blood group A glycosyltransferase human blood group B glycosyltransferase hyaluronic acid, hyaluronate hemagglutinin hyaluronate synthesizing enzyme hexosamine biosynthetic pathway hereditary erythroblastic multinuclearity with a positive acidifiedserum-lysis test (congenital dyserythropoietic anemia type 11) human chorionic gonadotropin heparin high endothelial venules human immunodeficiency virus hepatic lectin high mobility group (proteins) hemagglutinin-neuraminidase high performance liquid chromatography hydroxyproline-rich glycoprotein heparan sulfate highly sulfated domain heparan sulfate proteoglycan hemolytic uremic syndrome intercellular adhesion molecule iduronic acid insulin-like growth factor immunoglobulin immunoglobulin superfamily of proteins interleukin inositol phosphoglycan international unit
LX
K kb kDa Kdn
Abbreviations Used in Volumes 3 and 4
kinase enzyme activity coefficient kilobase (thousand base pairs) kiloDalton 2-keto-3-deoxy-nononic acid, formally 5-desamino-5-hydroxyneuraminic acid 2-keto-3-deoxy-~-manno-octulosonic acid Kdo kinase enzyme activity coefficient, at equilibrium Keq kinase enzyme activity coefficient, for inhibition Ki kifunensine KIF kinase enzyme activity coefficient, for structural modification(s) Km keratan sulfate KS keratan sulfate proteoglycan KSPG lactosamine LacAm N-acetyllactosamine LacNAc leucocyte adhesion deficiency LAD lysosomal associated membrane protein LAMP lipopolysaccharide-binding protein LBP Lewis a, Lewis x determinants Lea, Le" leucine Leu lectin and nucleotide phosphohydrolase LNP lipopoly saccharaide LPS lipoprotein receptor-related protein LRP leucine-rich repeat (amino acid/protein) LRR lysine LYS monoclonal antibody mAb mucosal addressin MAd myelin-associated glycoprotein MAG MALDI-TOF matrix-assisted-laser desorption ionization time of flight inass spectrometry mannose Man microtubule-associated protein MAP MBP-associated serine protease MASP mannose-binding lectin MBL mannose-binding protein MBP mannosyltransferase Man-T macular corneal dystrophy MCD Madin-Darby bovine kidney (cells) MDBK Madin-Darby canine kidney (cells) MDCK major histocompatibility complex MHC molecular weight mol.wt. mannose 6-phosphate receptor MPR mucopolysaccharidosis MPS apparent molecular weight Mr multiple sulfatase deficiency, Austin disease MSD N-acetylated disaccharide unit NA N-acetyl NAc
Ahhreviutions Used in Volumes 3 and 4
nAChR NAm NANA NCAM NDP NDST NEM NGF NIH NK NMR NS ORF OST P PAMP PAPS PARP PRL PCR PDGF PDI PEP PG PGM PI pNP-a-Man PNS PRP PSA PSGL-1 PTG RA RAr RACE rER RHAMM RT-PCR SA SAP SAT SBA SDS-PAGE Se Ser SGC
nicotinic acetylcholine receptor neuraminidase N-acetylneuraminic acid neural cell adhesion molecule nucleoside-diphosphate N-deacetylaselN-sulfotransferase N-ethylmaleimide nerve growth factor National Institutes of Health natural killer nuclear magnetic resonance N-sulfated disaccharide unit open reading frame N-oligosaccharyltransferase phosphate pathogen-associated molecular pattern phosphoadenosine phosphosulfate procyclic acidic repetitive protein peripheral blood leucocytes polymerase chain reaction platelet-derived growth factor protein disulfide isomerase phosphoenolpyruvate phosphatidylglycerol phosphoglucomutase phosphatidylinositol p-nitrophenyl-a-D-mannoside peripheral nervous system proline-rich protein polysialic acid P-selectin glycoprotein ligand-1 peptidoglycan retinoic acid rheumatoid arthritis rapic amplification of cDNA ends rough endoplasmic reticulum receptor for hyaluronan-mediated motility reverse transcription polymerase chain reaction sialyl saposin sialyltransferase soybean agglutinin sodium dodecylsulfate-polyacrylamide gel electrophoresis secretor enzyme serine sulfogalactosyl ceramide
LXI
LXII
Abbreviations Used in Volumes 3 and 4
SGG SGGL SGLT sia sLea, sleX SLRP SMC ST
sv
SW TCR TGF TGN Thr tlc TM t-PA UDP UDP-Gal UMD UMP UTP UV
vc
VE VL VSG
vsv
VT vWF WBP XYl ZP
sulfogalactosyl glycerolipid sulfoglucuronyl glycolipid sodium-glucose transporter sialic acid sialylated Lewis a, sialylated Lewis x determinants small leucine-rich proteoglycan sialomucin complex sulfurotransferase synaptic vesicle-associated protein swainsonine T cell receptor transforming growth factor trans Golgi network threonine thin layer chromatography transmembrane tissue plasminogen activator factor uranyl diphosphate UDP-a-D-galactose unmodified domain uranyl monophosphate uranyl triphosphate ultraviolet vitelline coat vitelline envelope vitelline layer variant surface glycoprotein vasicular stomatis virus verotoxin von Willebrand factor wheat germ agglutinin binding protein xylose zona pellucida
Part I
Volume 1
I Chemical Synthesis of Glycosides
Carbohydrates in Chemistry and Biology Beat Ernst, Gerald W. Hart, Pierre Sinay copyrightQ WILEY-VCH Verlag GmbH, 2000
1 Introduction to Volumes 1 and 2
As no better man advances to take this matter in hand, I hereupon offer my own poor endeavours. I promise nothing complete; because any human thing supposed to be complete must for that very reason infallibly be faulty. (from Moby Dick, Herman Melville)
Our understanding of the relationship between carbohydrate structure and biological function is still far behind that of proteins and nucleic acids. Initially, carbohydrates were only recognized as structural and energy storage molecules (e.g. cellulose, chitin and glycogen). The development of novel tools to study carbohydrate function has permitted additional biological functions to be elucidated. Their roles in protein folding, cell signaling, fertilization, pathogen binding to host tissue, leukocyte trafficking and associated inflammatory responses, tumor cell metastasis, and regulation of hormone and enzyme activities are just a few selected examples. These findings led to an immense interest in the preparation of oligosaccharides and glycoconjugates as well as the understanding of their interaction with their natural receptors. Part 1 of Carbohydrates in Chemistry and Biology is designed to be a valuable collection of chemical and enzymatic methods for the synthesis of oligosaccharides. It also covers state-of-the-art knowledge of the interactions of carbohydrates with their natural receptors. Each of the chapters is written by a leading expert in the field and covers an impressive body of references. Volume 1 of the series begins with the most challenging aspect of synthetic carbohydrate chemistry, namely the stereospecific formation of glycosidic bonds. A number of chapters describe recently developed approaches and cover numerous significant advances in glycosidation techniques. Other chapters review the attachment of sugars through linkages not occurring in nature. Volume 1 concludes by summarizing one of the most exciting and rapidly evolving area in modern carbohydrate synthesis: the use of glycosyl transferases and glycosidases in the synthesis of oligosaccharides and their analogs.
4
1 Introduction to Volumes 1 and 2
Volume 2 of the series covers the interactions of carbohydrates with their natural receptors, i.e. proteins, nucleic acids, and other carbohydrates. Whereas carbohydrate-protein interactions are well documented, the investigation of carbohydratenucleic acid and carbohydrate-carbohydrate interactions is an emerging area. The Carbohydrates in Chemistry and Biology series provides a comprehensive and up-to-date compilation of information on the fields of glycochemistry (Volumes 1 and 2) and glycobiology (Volumes 3 and 4),available today. The volumes not only provide an expert overview of the entire field, but also serve as a valuable reference tool to both, established investigators and students in many disciplines. The editors are obliged to all authors for their excellent contributions. Special thanks goes to Dr. Anette Eckerle, Wiley-VCH, who managed the realization of this series. Beat Ernst, Ph.D. Professor of Molecular Pharmacy University of Base1 Pierre Sinay, Ph.D. Professor of Organic Chemistry Ecole Normale SupCrieure, Paris
Carbohydrates in Chemistry and Biology Beat Ernst, Gerald W. Hart, Pierre Sinay copyrightQ WILEY-VCH Verlag GmbH, 2000
2 Trichloroacetimidates Richard R. Schmidt and Karl-Heinz Jung
2.1 Introduction Glycoside bond formation generally requires activation of the sugar at the anomeric center. To this end, activation through anomeric oxygen-exchange reactions (the classical Koenigs-Knorr method and its modifications, sulfur based activations, etc.) or, alternatively, activation through retention of the anomeric oxygen (trichloroacetimidate method, phosphite and phosphate activation, etc.) have been proposed. The trichloroacetimidate method is well established [ 1-1 31 and although the first paper on this method was published as recently as 1980 [ 141 it has already become a classical method. This is essentially because only catalytic amounts of a promoter are required to provide very high glycosyl donor properties whereas the anomeric oxygen-exchange based methods generally require at least equimolar amounts of a promoter system, which is obviously often associated with disadvantages of various kinds. The basic principle of the trichloroacetimidate method [ 11 consists in a simple base-catalyzed addition of trichloroacetonitrile to the anomeric hydroxy group to generate the 0-glycosyl trichloroacetimidate (see Scheme 1). This reaction is generally high-yielding and, because of its reversibility, high anomeric control can often be achieved; in addition, competing reactions with non-anomeric hydroxy groups are not observed. In the second step, under mild acid/Lewis acid catalysis glycosylation of various nucleophiles (for instance, of alcohols, etc.) can be readily achieved; in general high yields and high anomeric control are obtained. The anomeric control is derived from the glycosyl donors’ anomeric configuration (inversion or retention), from anchimeric assistance, from the influence of the solvent, or from thermodynamic or kinetic effects [ 1- 131. Since 1980 (up to the end of 1998), application of the trichloroacetimidate method has been reported in more than 1100 papers and over 1200 different 0glycosyl trichloroacetimidates have been described in the literature. Obviously, the wealth of this chemistry cannot be compiled in a relatively short book chapter. A
6
*OH
2 Trichloroacetimidates
.
Base Catalysis
CI&
Reaction with CI&-CN not observed
- C - NH, .
:: t
Mild Aci? Catalysis
4 +
+OyNH
CCI,
HOR
Scheme 1.
quite comprehensive review [ 71 on the trichloroacetimidate method appeared in 1994, and this chapter is, therefore, essentially devoted to the literature since 1994. Of 686 references (1994-1998) on the use of the trichloroacetimidate method, because of space limitation, only ca 220 references are considered in this chapter. The typical examples selected illustrate the application of this method in different areas.
2.2 Methods The reported methods [ 141 for the formation and reaction of trichloroacetimidates are well established. Use of sodium hydride or cesium carbonate as a base for the reaction of 1-0-unprotected sugars with trichloroacetonitrile yields generally the thermodynamically favored 0-a-glycosyl trichloroacetimidates, whereas use of potassium carbonate yields 0-p-glycosyl trichloroacetimidates because of kinetic reaction control. Use of 1,8-diazabicyclo[5.4.01undec-7-ene (DBU) often yields a/p mixtures, mostly favoring the a-trichloroacetimidates. Recently, application of new base systems has been reported using 7-methyl-l,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) [ 151 or phase transfer catalysis (50% potassium hydroxide, dichloromethane, tetra-n-butylammonium hydrogen sulphate) which yield exclusively atrichloroacetimidates in very good yields (96%) [ 161. Besides the well established catalysts for glycosylation reactions with trichloroacetimidates, some new catalysts have been investigated. The use of silver trifluoromethanesulfonate in the reaction with phthalimido-protected glucosamine trichloroacetimidate gave higher yields and smaller amounts of a-glucoside than the use of boron trifluoride etherate; this procedure also avoids acyl migration in the acceptor molecule; but stoichiometric amounts of the promoter are required [ 17,
2.3 Q-Glycosides
7
IS]. Use of lithium perchlorate in dichloromethane requires a large excess of promoter [ 19, 20 1, but with lithium trifluoromethanesulfonate only 0.05 equivalents are required [21]. Both catalysts give high yields, but the a/P selectivity is low and has to be improved before general application is possible. The synthesis of other 0-glycosyl imidates, i.e. O-glucopyranosyl dichlorocyanoacetimidates, 2,3,5,6-tetrafluoropyridin-4-y1 glucopyranosides, etc., is under investigation [22, 231 thus variations in reactivity and selectivity are expected.
2.3 O-Glycosides 2.3.1 Synthesis of Oligosaccharides
P-Glucosides, P-Galactosides, a-Rhamnosides, etc. 1,2-trans-glycosides (P-glucosides, 0-galactosides, P-xylosides, a-mannosides, arhamnosides, etc.) are usually prepared with glycosyl donors containing participating neighboring groups (acetyl, benzoyl, pivaloyl, etc. ) at 2-OH. Some examples for Galp(1-3)Gal [24], GalP(1-3)GalN [25], and ~-Rhaa(l-2)Glc[26] are shown in Scheme 2. Instead of the methyl glycoside of azidogalactose, the corresponding glycosyl fluoride has also been used as acceptor [27]. In general glycosylation yields are high, irres,pective of the anomeric configuration of the trichloroacetimidate, and only one anomer is obtained. Occasionally, when glycosyl acceptors with more than one free OH group are used, high regioselectivity is obtained because of the different reactivity of the OH groups. It was found that trichloroacetimidate donors are especially appropriate for deactivated (fluorine containing) donors in contrast to other glycosyl donors (thioglycosides, etc.) [28]. A highly convergent synthetic method has been developed for the synthesis of cellooctaose and other cello-oligosaccharides via di- and tetrasaccharides which can be converted either into glycosyl donors by deallylation and transformation into the trichloroacetimidates, or into acceptors by deacetylation (Scheme 3) [29].The use of p-methoxybenzyl groups (PMB) instead of acetyl groups was less successful. The combination of acetyl, pivaloyl, and benzyl groups leads to the proper balance between stability and reactivity of trichloroacetimidates as donors and the acceptor substrates. High yields were achieved by using a specially developed high-vacuum system for glycosylations under anhydrous conditions. Trichloroacetimidates have also been used for the glycosylation of more complex carbohydrate acceptors (Scheme 4). Galp( 1-3)GlcN and other disaccharides were synthesized and converted into fluorescein-labeled acceptors which are used for sialyltransferase assays [301. Glucosyl diosgenine has been used as carbohydrate acceptor for further glycosylations with various trichloroacetimidates (Scheme 4) [31, 321. All glycosides were obtained in high yields and high stereoselectivity because of participating neighboring groups at 2-OH in the synthesis of dioscin, polyphyllin D, balanitin 7, and gracillin.
8
2 Trichloroacetimidates
Baw Bzo
OBI
+
BZO
Hr&
OCH3
75%
OBZ
BzO
OBz
HO
OBZ
GalP(1-3)Gal OBZ
Ph
OAc
OBz
BZO~ O ! & & O C H ,
Aug6 et al. 1241
O YCCI, NH
AcO
.
CH TMSOTf CI ,O°C
Ph
TMSOTf CICH,CH,CI,,
-1 8%
Ga@(1-3)GalN
AcO OAc
Bock et al. [251
CCI,
N,
CCI, Ad)
OANH
BFS. OEtz A
c O AcO
H
+
0 OAll
CH,CI,, -20°Cb
AcO OAll
OAc
L-Rhaa(1-2)Glc
95% Liu et al. "261
A c O AcO R q
+
6
HO BnO
0
PhtN
I
O YCCI, NH
R = OAC, H, F
R
I cot
TMSOTf CH2C12,00C CHzCIz,OoC
*
93%
93%
A
C
~ W AcO
~
Karnerling et al. [281
,OBn
O
-
~ PhtN
I
BZ& BnO BnO
0C8H17
Scheme 2.
Aminosugar Trichloroacetimidates The use of azidosugars and N-phthalimido-protected aminosugars is well established in carbohydrate chemistry. But many new protective groups have been proposed to enable deprotection under milder conditions or to apply orthogonal protection strategies (Scheme 5). For the synthesis of P-glycosides of aminosugars, protective groups with amide structure are mainly used; these are capable of neighboring group participation. But formation of stable oxazolines reduces the reactivity of the glycosyl donors, and phthaloyl groups are therefore preferred. They can be cleaved only under strongly basic conditions, for instance, with hydrazine. As an alternative, the use of the tetrachlorophthaloyl (TCP) group has been proposed [33];this can be more readily removed with ethylenediamineor with sodium borohydride followed by acid treatment (pH 5). The glycosylation reaction gives excellent yields and in acetonitrile as solvent exclusively the P anomers are obtained. Further applications of TCP-protected trichloroacetimidates are shown below (glycosyl amino acids, C-glycosides).
2.3 0-Glycosides
9
OAll
1. Se02IAcOH
bpiv
OPiv
HBnOo
~
O A OPiv
I
I
BnO OPiv
/
disaccharide-
OPiv
\
disaccharide-
BnO
OPiv
OPiv
OPiv
tetrasaccharideimidate
OPiv
tetrasaccharideacceptor CH&,
O°C
Nishimura, Nakatsubo 1291
OPlV ACO BnO
OPlV
BnO OPlV
OPlV
OPlV
OPlV
OPlV
Scheme 3.
Similar properties have been observed for 4,5-dichlorophthaloyl (DCPhth) protected trichloroacetimidates [ 341. Deprotection can be performed with ethylenediamine. The trichloroethoxycarbonyl (Teoc, Troc-both abbreviations are in use) group has already been applied successfully to aminosugars [35].Because it can be cleaved under reductive conditions (with zinc) it can be used for base-labile compounds and more importantly for demanding orthogonal protection strategies. For glycosylation reactions with N-Teoc-protected trichloroacetimidate-activated aminosugars very high yields and stereoselectivities are reported [36]. Application was also shown for the synthesis of some complex Lipid A analogs [37-391. Glycosylation of acceptors with Teoc-protected trichloroacetimidates, both containing long chain fatty acid residues, was performed in high yields and stereoselectivities. Further applications (glycolipids, glycopeptides, bacterial polysaccharides, solid-
10
2 Trichloroucetimidates
HO HO&
"Po AcHN
BF,.OEt,
+
CCI,
CH~CI, 76%
-
1. deprotection
HO
OH
2. fluorescein isothiocyanate
O(CH,),NHCbz NHAc
Slim et al. [301
HO
CCI,
AAcOc O ~ 6 ; * o I c c , , OAc
AcO
OH
OAC CCI,
L-Rhaa(l-2)GlcP(l-O)diosgenine (dioscin)
Xyl~(l-3)Glc~(1-2)Glc~(l-O)diosgenine (balanitin 7)
L-Araa(1-2)GlcP(1-0)diosgenine (polyphyllin D)
Glc~(1-3)Glc~(l-O)diosgenine
I
Rhaa(1-2)
(gracillin)
Hui et al. [31,321
Scheme 4.
phase synthesis) of Teoc-protected trichloroacetimidates are shown below. Similar results were obtained with p-nitrobenzyloxycarbonyl (PNZ) protected trichloroacetimidates [40]. Deprotection can be performed under reductive conditions either with hydrogen and palladium-on-carbon or with sodium dithionite under neutral or slightly alkaline conditions. If protective group manipulations are incompatible with basic or reductive conditions, use of the 2,5-dimethylpyrrole group is proposed; this can be treated with hydroxylamine hydrochloride to liberate the amino group [41, 421. Glycosylations with dimethylpyrrole containing trichloroacetimidates perform well, leading selectively to P-glycosides (1,2-trans-glycosides). Recently the dimethylmaleoyl (DMM) group has been proposed as an amino-protecting group which can be cleaved under mild aqueous basic and then acidic conditions (pH 5 ) [43]. Because of the anchimeric assistance and the electron-withdrawing character of the DMM group the corresponding trichloroacetimidates give stereoselectively P-glycosides in high yields. The dithiasuccinoyl (Dts) group [44] for amino group protection is discussed below (glycopeptides).
11
2.3 0-Glycosides BnO A AcO c o ~ O y C C l , +
TCPN
OH
n BnO O OBn q CH,CN, 91% r.t.
B
NH
81%
BnO 0
BnO
CI OBn
TCP = tetrachlorophthaloyl,
Castro-Palomino, Schmidt [33]
CI
0
CI
1. TMSOTf HO DCPhthN
73%
OMP
BnO DCPhthN
NH
0
OBn
AcNH
3. AcpO, pyridine 84%
wz:
DCPhth = 4,5-dichlorophthaloyl,
b
2.ethylenediamine
Ogawa et al. [34]
0 BnO
--,
0
Teoc = trichloroeihoxycarbonyl,
-k!
R = (S)-3-(tetradecanoyloxy)tetradecanoyl = (S)-3-(dodecanoyloxy)tetradecanoyl R" = (S)-3-(benzyloxy)tetradecanoyl
-OCH,CCI,
(Troc)
% % ;A
+
PNZ'
BnO
1. TMSOTf
NH
1. BF,.OEt, CHZCI,, -3OC
&
HO BnO
2. NaOMe, 79% quant.
OBn
OBn
'yNH
.
3. Na,S,O, quant. 4. Ac,O, pyr., 93% C
H NO,
OBn
AcNH
0
CCl,
PNZ = p-nitrobenzyloxycarbonyl, - - O
Kusumoto et al. [37-391
Quian, Hindsgaul [40]
~
1. TMSOTf
CCI,
--
OCH,
~~~&o,cc13 DMMN
6
HO BnO
AcO
NH
DMM = dimethylmaleoyl,
OBn
+
1. TMSOTf C 78% H,CI,
2.NaOH 3.HCI 4. Ac,O 97%
0 $CH3 CH,
Scheme 5.
OBn
CHZCI,, -25C 78% 2. NEt,,MeOH, H,Ob 3. NH20H, 8OC 4. Ac,O, pyr.
r. t.
.
AcO
BnO OCH.
Boons et al. [41]
AEoa:o+OBn AcNH
OBn
Schmidt et al. [43]
12
2 Trichloroacetimidates CONH,
CONH,
ACO
31% OAc 0
Welzel et al. 1461
TMSOTf CH,Cldhexane, 60%
r.?
Bnd
Scheme 6.
Finally, the synthesis of moenomycin-type analogs is described (Scheme 6). Use of the trichloroacetyl protecting group for aminosugar trichloroacetimidates as previously proposed [45] gave the desired disaccharide (31% yield) [46]. Because of silyl group migration under the glycosylation conditions, the tri-TBS-protected acceptor, the diglycosylated acceptor, and the oxazolidine of the donor were also formed as by-products. The trichloroacetyl group can be converted into the acetyl group either with zinc-acetic acid or with tributyltin hydride in the presence of AIBN. Better results were obtained with a 2-(trimethylsilyl)ethanesulfonyl-protected trichloroacetimidate [47].The desired P-glycoside was obtained stereospecificallyin 60% yield and further transformations are under investigation. Trichloroacetimidate derivatives for the preparation of aminosugar a-glycosides (1,2-cis-glycosides)are rare. The use of azidosugars is well established (examples are given below), but unfortunately they are not readily available. Azidoglucose, for example, is prepared either from glucose via glucal by azidonitration [48]or from glucosamine via diazo transfer with trifluoromethanesulfonyl azide [49]. The N-l(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl (Dde) group has been proposed as non-participating neighboring group for the synthesis of 1,2-cis-glycosides(Scheme 7) PI.
,OAc
Kellam et al. [501
ACO
DdeNH
~~
. .. .
0
Dde = N - l - ( 4 , 4 - d i m e t h y l - 2 , 6 ~ 1 x ~ c y c l ~ h e x ~ ~ ~ e ~ e ~ ~ ~ h y Scheme l a e n e ) e7.t 0
2.3 0-Glycosides
13
65%
CCl,
Furstner, Konetzki 1541
Scheme 8.
P-Mannosides
The synthesis of p-mannosides is crucial because p-mannoside formation is disfavored because of stereoelectronic and steric reasons. Besides the already known direct mannosylation reactions some indirect approaches which have been reported are based on the preparation of I)-glucosides and then inversion of the configuration at C-2 to yield the corresponding P-mannosides (Scheme 8). According to a previously introduced method [ 5 11, a p-glucoside, synthesized using a trichloroacetimidate as glycosyl donor, was converted into its 2-0-triflate [ 521. Intramolecular nucleophilic substitution afforded a Mano( 1-4)GlcNp( 1-4)GlcN trisaccharide occurring in the core-region of glycoproteins. In other examples 2-0-triflate intermediates were subjected to intramolecular nucleophilic substitution under inversion of the configuration by reaction with tetrabutylammonium nitrite [53] (see below, Scheme 26) or with tetrabutylammonium acetate [54]. The reaction has been significantly improved by means of ultrasound, but very good yields have been also obtained previously via a sulfonyl imidazylate [55]. 2-Deoxyglycosides
Direct glycosylation with 2-deoxyglycosyl donors is not employed because the corresponding glycosyl donors are quite labile and they lack stereocontrol by anchimerically assisting groups. A recent application of a previously developed method [56] has been reported; it uses a 2-deoxy-2-thiophenylglucosyltrichloroacetimidate which can be readily prepared from glucal (Scheme 9) [57]. After glycosylation the thiophenyl group can be removed by reduction methods. Because glucal is not readily available as starting material and the stereoselectivity of the glycosylation of carbohydrate acceptors is critically dependent on substituent X
14
2 Trichloroacetimidates
ROH, TMSOTf CH& -78% &I3
& '*OR TBDMSO
- -re$- - -b
Roush et al. [571
X = OTos, Br, H
BnO BnO
TBDMSO -&OR
PhS
a -unu- I
OCH.
1. TMSOTf
91% L 2. BuqSnH, AlBN 74%
-
BnO I
OCH.
Castro-Palomino,Schmidt I581
Scheme 9.
at the 2-position, a new method has been proposed. Glycosylation reaction with 2-O-thiobenzoyl-protected O-glucosyl trichloroacetimidates gave exclusively the 0-glucosides which could be converted into the 2-deoxy-P-glucosides by reduction with tributyltin hydride [58]. Starting from mannosyl trichloroacetimidates the 2-deoxy-a-glucosides were obtained in the same manner [ 5 8 ] . Miscellaneous Compounds
The synthesis of some rare glycofuranosyl donors has also been reported (Scheme 10). The trichloroacetimidates of D-glucofuranose [59], D-mannofuranose [59], and D-galactofuranose [59, 601 have been prepared and used for the synthesis of furanosyl glycosides. With the heptosyl trichloroacetimidate some neoglycoconjugates containing Hep( 1-4)Kdo and Hep(1-5)Kdo-4-phosphate-(2-6)GlcNAcresidues were synthesized which are part of the inner core region of bacterial lipopolysaccharides [61]. A 5-thio-~-fucosyltrichloroacetimidate was used for the synthesis of 5-S-~-Fuca( 1-2)Gal and other disaccharides which have inhibitory activity against a-L-fucosidases [621. Some 5-thiomannose-containing oligosaccharide mimetics were prepared with a 5-thiomannosyl trichloroacetimidate; their binding constants to concanavalin A were determined [63]. An example of intramolecular glycosylation has been reported with a Glca(12)Glc trichloroacetimidate [64, 651. Reaction with boron trifluoride-diethyl ether gave the cyclo-a(1-2)glucobiose (cyclokojibiose) with concomitant expulsion of the O-benzyl protecting group. 2-O-debenzylation previous to cyclization is not necessary because the oxygen is sufficiently nucleophilic and the reaction is entropically favored. A similar example has been reported with a fucose moiety [66]. Complex Oligosaccharides
Complex oligosaccharides are major parts of many biomolecules (glycolipids, glycoproteins, bacterial lipopolysaccharides, mucopolysaccharides, etc. ) and they have a variety of functions. Much interest has been focussed on Lewis antigen structures which are found in glycosphingolipids and on glycoproteins. Many syntheses have
2.3 0-Glycosides
15
AcO AAco & * I
O YCCI, NH
CCI,
LOB"
Plusquellec et al. 1591
Roy et al. 1601
Kosma et al. (611 HO O ,H
&
A d
OAc NH A d
OAc
+
Hashimoto et al. 1621
OAll
OH
BF3.OE1, CH2C12,-2OOC 86%
*
--b H : + HO
OH
,.OAc
Scheme 10.
been described for the Lewis' antigen (LeX)structure which has been found to be a tumor-associated antigen, and for the sialyl LewisX(s LeX)epitope which is involved in cell-adhesion and inflammation processes mediated by its binding properties to selectins. Several synthetic strategies with various building blocks and/or different protective group patterns have been employed, but in recent investigations two alternatives have been favored. A suitably protected azidolactose building block which is available from lactose via lactal, has been chosen (Scheme 11) because it already contains the desired Galp( 1-4)Glc:N linkage [67]. Because of the non-participating neighboring group at 2-OH, fucosylation proceeded exclusively to the a-glycoside and gave the LeXtrisaccharide repeating unit in very good yield (97%). Transformation into the trichloroacetimidate and coupling with the lactose moiety gave spacer-linked Le" which could be extended with the trisaccharide trichloroacetimidate into the spacerlinked dimeric LeXantigen. Following the alternative strategy (Scheme 12), an azidoglucose building block was chosen as starting material and glycosylated first with fucosyl trichloroacetimidate and after benzylidene ring opening with galactosyl trichloroacetimidate [68]. Both glycosylations were highly stereoselective and gave, because of suitable neighboring groups and reaction conditions, exclusively the anomers desired. The high yields were based on the use of the 'inverse procedure' (i.p.), i.e. addition of the trichloroacetimidate donor to the acceptor-catalyst mixture. The LeXtrisaccharide repeating unit was then transformed into the trichloroacetimidate donor and into the glycosyl acceptor and then coupled with trimethylsilyl triflate as catalyst in
16
2 Trichloroucetimidutes
NH
OBI
OBn
97%
Aco
OBZ
Windrnuller, Schmidt [671
Scheme 11.
~
h
T t HO
-
~
N3
~
~
~
TMSOTf, i.p. Et,O, r.t. 85%
TMSOTf, i.p. Et20, r.t. 71%
trisaccharide
hexasaccharide irnidate acceptor N3
imidate 081
dodecasaccharide imidate
n = 2 : dim.LeX n = 3 : trim.LeX n = 4 : tetram. LeX
Scheme 12.
Schmidt et al. 68
17
2.3 0-Glycosides
acetonitrile as solvent to yield stereospecifically the P-connected hexasaccharide by means of the 'nitrile effect'; this effect is particularly efficient with 2-azido sugars. The nonasaccharide and dodecasaccharide were prepared in the same way by coupling the hexasaccharide trichloroacetimidate with the tri- or hexasaccharide acceptor. Transformation into the trichloroacetimidates and reaction with the lactose acceptor yielded the octa-, undeca-, and tetradecasaccharides. After coupling with azidosphingosine and further transformations the dimeric, trimeric, and tetrameric Le" antigens were obtained. The synthesis strategy is highly convergent and allows variations in the saccharide structure and the lipid moiety. The ready a.vailability of glucosamine was reason to transfer this synthesis strategy to glucosamine building blocks which can be obtained directly from glucosamine. The N-tetrachlorophthaloyl (TCP) [69], N-trichloroethoxycarbonyl (Teoc) [70], and N-phthalimido (Pht) [711 protected glucosamine acceptors were glycosylated with the 0-galactosyl and 0-fucosyl trichloroacetimidates; both reactions proceeded with high stereoselectivity. The resulting Le" trisaccharide repeating unit was transformed to the corresponding trichloroacetimidates which were used for the glycosylation of the lactose acceptor to give, owing to neighboring group participation, the p( 1-3)-linked Le" pentasaccharide. The Lewisa (Lea) antigen is a blood group antigen; because of its structural similarity to the Re" antigen it has been synthesized in a similar manner (Scheme 13) [72]. The benzylidene-protected azidoglucose acceptor was first glycosylated with galactosyl trichloroacetimidate and, after benzylidene ring opening, with fucosyl trichloroacetimidate; both glycosylations could again be performed with high diastereoselectivity. Transformation into the trichloroacetimidate and reaction with the CCI,
CCI,
OTBS
TMSOTf Et20, r.t. 88%
N3
Ph T HO a O
T
D
BnO
TMSOTf, i.p. Et20, r.t.
AcO
*
OAc
78%
S
I
0KCC'3 NH
BF, OEt2 CH,C12, hexane
H
Schmidt et al. [;TO]
o
#
~
o
~
O
OBn B n
'
61%
FUCCU(~-4) HHO
O
aOTDS NTCP
Schmidt et al. [69]
Hio&
OTBS
I
Gal~(I-3)GlcNAc~(1-3)Gal~(1-4)Glc
N,
Toepfer, Schmidt [72]
Lea Toepfer, Schmidt [72]
Scheme 13.
18
2 Trichloroacetimidates
lactose acceptor in a non-polar solvent as catalyst with diethyl ether-boron trifluoride gave the Lea pentasaccharide. The p-linkage was stereospecifically formed under inversion of the configuration; typical conditions for this reaction type were used. The N-trichloroethoxycarbonyl (Teoc) protected glucosamine acceptor was proceeded in the same way [70]. The Lea trisaccharide was also prepared from the 3,4-di-O-unprotectedazidoglucose [72] and N-tetrachlorophthaloyl (TCP)-protected glucosamine [69] acceptors by attachment of the two sugar residues directly one after the other. The blood group antigen H and the LewisY (Ley) antigen, a stage-specific embryonal antigen (SSEA), have been synthesized using the same azidolactose building block (Scheme 14) [67]. By regioselective monofucosylation and by difucosylation of the 3,2'-di-O-unprotected azidolactose acceptor, the H-antigen trisaccharide and the Ley tetrasaccharide were synthesized in high yields. Transformation into the trichloroacetimidate and coupling with the lactose moiety furnished the spacer-
CH,Cl$hexane BF,.OEt, -10%
70%
!
o(cHd&~H, HO
OBZ
Ga@(1-4)GlcNAcp(1-3)Ga@(1-4)GlcP(1-0)Sp FuW( 1-2)
H-antigen
I
BFS.OEt2 CH,Cldhexane
H O + O - Y
OBZ
-1O°C
71%
F u c ~1(-2) F u c ~1(-3) Windmuller, Schmidt I671
Scheme 14.
2.3 0-Glycosides
19
-
trisaccharide imidate
BnO
--+ trisaccharide N3
TMSOTf. i.p. Et,O
TMSOTf, i.p. EtPO
85%
89%
acceptor BnO
TMSOTf CHSCN, -4OC 80%
I
COOCH,
FUctr(1-3)
dim. sLeX
1:
octa-
hexasaccharide imidate
Fuca(1-2) Galp(l-4)GlcNAcp(l-3) alp(l-4)Glcp(l-I)Cer
[
F U C ~-3) ('~
I
dim.LeY
BnO
Hummel, Schmidt [73]
Scheme 15.
linked H-antigen and Ley antigen, respectively. Another strategy has been applied to the synthesis of the dimeric Ley antigen (Scheme 15) [73]. According to the previously described synthesis of dimeric LeX (Scheme 12, Ref. [68].) the Le' trisaccharide has been prepared from the azidoglucose acceptor, the fucosyl and the galactosyl trichloroacetimidate, and the derived trisaccharide was used as trichloroacetimidate donor and as acceptor for the synthesis of the corresponding hexasaccharide. Coupling with the lactose moiety gave the octasaccharide which was subjected to a protective group change at the terminal galactose moiety. Regioselective protection of the 3-OH, 4-OH, and 6-OH groups and fucosylation at 2-OH gave the desired nonasaccharide. After coupling with azidosphingosine and further transformations the dimeric Ley antigen was obtained. For the synthesis of the sialyl Lewis' (sLe') antigen, the terminal galactose moiety of the octasaccharide was 6-0-benzyl-protected. Regioselective glycosylation of the 2,3,4-tri-O-unprotected acceptor with neuraminic acid phosphite as donor gave the desired 3-0-sialylated oligosaccharide which was coupled with azidosphingosine and transformed into the dimeric sLe' antigen by use of established methods. Further syntheses of the sLe' determinant follow the same strategy, but applying other glycosylation methods (Scheme 16). Fucosylation of a similar O-benzylideneprotected glucosamine acceptor performed well with a thioglycoside donor [74-761, but the galactosylation was critical because of the steric hindrance of the 4-OH group. The methylthio galactoside donor gave a 16% yield [74]; the trichloroaceti-
20
2 Trichloroacetimidates
HNAC
Ga@(1-4)GlcNAcP-X NeuAca(2-3) Fuca(1-3)
= NH2
Kretzschmar, et al. [74-761
Scheme 16.
midate was, therefore, again favored. Regioselective sialylation with the thioglycoside donor gave the sLeXdeterminant bearing an amino group or a spacer at the reducing end for attachment to peptides or for the generation of other conjugates. The synthesis was suitable for large-scale preparations 1761 and enabled the use of sialic acid derivatives with modifications at C-5 to synthesize sLeXanalogs and to investigate their binding properties to E- and P-selectins [75]. A similar strategy for the synthesis of the sLeXdeterminant was used by applying the glycal method (Scheme 17) [77]. The 3,4-di-O-unprotected glucal was regioselectively fucosylated ( a : = 7.5: 1) with fucosyl fluoride and then galactosylated with 0-galactosyl trichloroacetimidate to yield the Le" trisaccharide glycal. The 2,3,4-tri-O-unprotected galactose acceptor was then regioselectively sialylated with sialyl chloride as donor. Then application of the glycal method gave either the sLeX trisaccharide or-by extension with the tributyltin derivative of the lactal acceptor -the sLeXpentasaccharide glucal derivative which can be activated to provide a donor for the synthesis of conjugates. The synthesis is efficient and convergent, and it is worth mentioning that for the crucial galactosylation of the sterically hindered 4-OH group the trichloroacetimidate method has again been employed. The synthesis of LeXor sLeXanalogs or simplified structures, so-called mimetics, is of great interest for binding studies with selectins, thus high affinity ligands concomitantly with convenient chemical syntheses for novel anti-inflammatory drugs are evaluated. The synthesis of some only slightly modified Le" analogs containing Glc instead of GlcNAc [78], GalNAc instead of Gal [79],or 5-thiofucose instead of Fuc [801 has been similarly performed as described above using trichloroacetimidate donors. It has been found that sialylations are always crucial and expensive processes, therefore many syntheses for sLeXmimetics have been developed in which
2.3 0-Glycosides
21
OTDPS OBn
OTDPS
A
c
O
g
O
&
BZO
AgC104 SnCI, DTBP 59%
OBn
BF,~OEt, CH& -78OC 73%
Bzo
Danishefsky el al. 071
Gal~(1-4)GlcNAc~(l-3)Gal~(l-4)Glucal
Galp(1-4)GlcNAc
NeuAca(2-3) Fuca(1-3)
NeuAca(2-3) Fuca(1-3)
Scheme 17.
AcO
BnO
AcO
a
O
B
OAc
Ph q 'HO a O A l l 0 0 ~
TMSOTf CH& 87%
I
AgOTf Bu,SnCI, 90%
b
F u c ~1-4) (
n
I
AcO W o OAc & O A I I
3'-phospho-Lea-analog AcO
OBn OAc
Kiessling et al. [Sll
3'-C-carboxymethyl OBZ OBn
DMTST TMSOTf benzene, 6OC CH,CN, -1OOC 86% 67%
OBn
b
'~6
BnOoBn @OBn
I
Kiso el al.[831
NHAc
HO
Scheme 18.
Thoma el al. I841
22
2 Trichloroacetimidates
HO
OH
Wong et al. IS81
Scheme 19.
neuraminic acid is replaced by other acids (Scheme 18). A 3’-phospho-Lea analog [81] and a 3’-sulfo-Lex analog [82] were prepared from 3-0-unprotected 4,6-0benzylidene-glucose derivatives. As well established in the synthesis of LeXand sLeX (see above), for all glycosylations with galactose the trichloroacetimidates were successfully used as donors. For the synthesis of the 3’-C-carboxymethyl LeXanalog [831 the synthesis and use of the required galactose-derived trichloroacetimidate donor has been reported. A more rigidly fixed carboxylic group is contained in the sLeXmimetic with a six-membered ring fused to galactose bearing an equatorial carboxylic acid group [84]. The required branched galactose moiety has been prepared and used as trichloroacetimidate-activated donor. Further sLeXmimetics with other simplifications have been proposed (Scheme 19). The GlcNAc moiety has been replaced by cyclohexanediol which was used as acceptor and glycosylated first with the galactosyl trichloroacetimidate and then with the corresponding fucosyl donor [85]. Then a malonic acid derived group was introduced at the 2-OH of galactose. In an even more simplified structure the galactose moiety has been replaced by an aliphatic chain [86]. The acceptor which was prepared from glucal is first glycosylated with the fucosyl trichloroacetimidate and then converted into the malonic acid derivative. In a related mimetic, the malonic acid group is attached more rigidly at a benzene ring [87]. Glycosylation with the
2.3 0-Glycosides
A*
OAC
COOCH,
OBn
23
OBn
(GM, intermediate) pentasaccharide imidate
Gal~(I-3)GalNAc~(1-4)Gal~(l-4)Glc~(l-1)Cer NeuAca(2-3)
Schmidt et al. [891
Scheme 20.
fucosyl trichloroacetimidate resulted in a low yield only (35%), because of steric hindrance. A c:ompletelydifferent structure has been chosen with a terpenoid system [88]. Glycosylation of isosteriol with the mannosyl trichloroacetimidate gave a mimetic which selectively inhibits P-selectin, but not E- and L-selectins. Glycolipids other than the Lewis antigens have also been synthesized with trichloroacetimidate donors. For the synthesis of the ganglioside GM1 several strategies have been suggested [89, 901. Applying a convergent strategy (Scheme 20) [89] a 3,4-di-O-unprotected lactose acceptor was first sialylated with neuraminic acid phosphite as donor to give a GM3 intermediate, and then glycosylated with a Galp( 1-3)GalN trichloroacetimidate as donor; the latter can be easily prepared from azidoglucose and galactosyl trichloroacetimidate. Coupling with azidosphingosine by application of trichloroacetimidate activation of the pentasaccharide residue and then further transformations yielded GMI . Another strategy via a C A I intermediate performing sialylation at a later stage has also been reported [90]. The GM3 intermediate is also suitable for the synthesis of GM2 [91]Glycosylation of the GM3 intermediate with the Teoc-protected galactosamine trichloroacetimidate, which can be more readily synthesized from galactosamine than azidogalactose from galactal, and application of the established transformations, yielded GM2 which is required in a cancer immunization study with GM2-containing vaccines. A glycolipid of the neolucto series named 3-0-sulfo glucuronyl paragloboside is also of interest because of its immunological properties (Scheme 21) [92]. The syn-
24
2 Trichloroucetimidutes COOMe
k0.d-
H:p&
BzOO
OBn OSE
HO
8
BnO
gn&
OBn OSE
OBn
CCl,
OSE
94% TMSOTf
CH,CI,, r.1.
pentasaccharide imidate
N3
BF,.OEt, CHZCI,, O°C 72%
00~S-0-3GlcAP(1-3)GalP(I-4)GIcNAc~(1-3)Gal~(1-4)Glc~(l-l)Cer
3-0-sulfo glucuronyl paragloboside
Hasegawa et al. [921
Scheme 21.
thesis is based on glycosylation of a lactose acceptor with phthalimidoglucosyl trichloroacetimidate. Glycosylation with a disaccharide trichloroacetimidate, which was prepared from a glucuronic acid trichloroacetimidate and a galactose acceptor, and the usual transformations including introduction of the sulfo group yielded 3-0-sulfo glucuronyl paragloboside. A more straightforward synthesis of a related structure has been reported using a Galb( 1-4)GlcN disaccharide (lactosamine) which is contained in the neolucto structure as starting material (Scheme 22) [93]. Glycosylation of the lactose acceptor with the azidolactosyl trichloroacetimidate donor followed by sialylation and application of the standard azidosphingosine glycosylation procedure gave the neolacto ganglioside LM1. All the above mentioned examples contain P-glycosidic linkages which can be obtained by means of participating neighboring groups or-for azidosugars-by means of the nitrile effect. The synthesis of gangliosides of the globo series which contain also an a-galactose linkage is more difficult. From the azidogalactosyl trichloroacetimidate and a galactose acceptor the 2-0-benzyl-protected disaccharide was prepared (Scheme 23) [94, 951; this was converted into the trichloroacetimidate and used as donor for the glycosylation of the lactose acceptor. Using typical conditions favoring s,~-type reactions (non-participating neighboring group, strong Lewis acid, diethyl ether as solvent), the a-connected tetrasaccharide was obtained with high selectivity. Ensuing galactosylation, sialylation, and application of the
25
2.3 0-Glycosides TMSOTf CH2C12,-4OOC (SOYO) tetrasaccharide
b
I OBn
58%
OBn
OEt
pentasaccharideimidate
5
lF3.0Et2 CH2C12,O°C 43%
O h
NeuAca(2-3)Gal~(l-4)GlcNAc~(l-3)Gal~(1-4)Glc~(I-1)Cer Tietze et al. [931
LMl
Scheme 22.
Ph
Ph
Ph
TMSOTf
&:s
Ho BnO
OAll
HO
N,
OBn
BnO
OBn
OBn
1
CCI,
0
Y
NH
Y CCI,
Ph
Ph
TMSOTf, i.p EbO, -1OOC
Bds+E;ohloBn TMSOTf I
-'I
Ell0
AcOO
vNH I CCI,
TMSOTf CH,CN, -4OOC-I (a$= 3.5:l)
%En
AcO
62%
AcN
COOCH,
dAc
hexasaccharide imidate
N,
TMSOTf OBZ
Neu5Aca(2-3)Gal~(l-3)GalNac~(l-3)Gala(l-4)Gal~(1-4)Glc~(1-1)Cer Schmidt et al. 194,951
Scheme 23.
SGG
26
2 Trichloroacetirnidates
azidosphingosine glycosylation procedure yielded the sialylgalactosylgloboside (SGG), which bears the stage-specific embryonic antigen 4 (SSEA-4) structure. Another example of the globo series is the globo H (human breast cancer) antigen. It has been prepared by means of a similar strategy [96]. Although in glycopeptide synthesis, most strategies are based on the synthesis of the complete oligosaccharide moiety and then its attachment to the amino acid or peptide, glycosylations of glycosylated amino acid acceptors have also been reported (Scheme 24). Thus, glycosylation of the GalNa( I-0)Thr acceptor with
Ph
'%$
+
H
o
1. TMSOTf, CH2CI,, O°C 02%
b
2. Zn, &OH, AC20, THF 3. AqO. pyr. (80%)
TeocN
b
O YCCI, N H
core3
Fmoc[O X HC0,Bu' 3
FmocNH
Bock et al. [971 Ph
+
Ph
"q
Bock et al. 1441
1. TMSOTf, CH2C12,40°C 67% 2. Zn, 7OoC THF, AC20,HOAc)
AcNH
H
Ph
Ph
Ph
CCI,
Qiu, Koganti I981
w T s 0
'no
0
II
-15% 69%
AcN
OBn
Scheme 24.
OBn
OBn
OBn
2.3 O-Glycosides
27
N-trichloroethoxycarbonyl (Teoc)- [97] or the N-dithiasuccinyl (Dts)- [44] protected glucosamine trichloroacetimidates, respectively, afforded the core 3 building blocks. The P-glycosides were stereospecifically obtained by means of neighboring group participation. Use of the N-acetyl-protected galactosamine trichloroacetimidate gave stereoselectively the a-connected core 5 structure [98]. Thus, core 1, 2, 3 , 4, 5 , sialyl 5 , 6, and F1-a building blocks were synthesized [44, 97-99]. A sialylated glycosy1 serine building block was prepared with a disaccharide trichloroacetimidate donor and used in the solid-phase synthesis of the B-chain of human u2HS glycoprotein [loo, 1011. In the synthesis of branched complex type N-glycans the oligosaccharide part is usually prepared first; it is then attached to the amino acid, usually asparagine. For investigations of the function of glycoproteins the synthesis of libraries with variations of the antennary structures is required. A highly convergent chemoenzymatic approach has recently been reported (Scheme 25) [ 102-1041. The core trisaccharide Mar$( 1-4)GlcNP( 1-4)GlcN was synthesized via the P-glucoside and then inversion of the configuration by intramolecular nucleophilic substitution as described above (see Scheme 8:1, thus avoiding the crucial direct P-mannosylation. The trisaccharide acceptor is suitable for the attachment of various antennary structures with linear or branched trichloroacetimidate donors which were again synthesized by application of the trichloroacetimidate method. Several examples were prepared and used for investigations on further glycosylations with galactosidases and sialidases. Another versatile strategy enables the synthesis of diantennary and bisected diantennary oligosaccharides (Scheme 26) [ 531. The azidoglucose acceptor was glycosylated with the glucosyl and mannosyl trichloroacetimidates. The P-glucoside of the resulting trisaccharide was converted into the P-mannoside moiety by inversion of the configuration at C-2 via triflate formation and substitution with tetrabutylammonium nitrite. Further glycosylations with the mannosyl and the azidoglucosyl trichloroacetimidates gave the bisected diantennary pentasaccharide which was used as acceptor for extension with lactosamine trichloroacetimidate. After transformation of the nonasaccharide into the trichloroacetimidate the terminal glucosamine residue was attached at the reducing end. Thus, the synthesis is highly variable in the connection to the protein and in the antennary structures. Further syntheses applying direct 0-mannosylation have also been reported [ 105- 1071, and it was found, that the trichloroacetimidate method was superior to other glycosylation methods, especially for the synthesis of u-mannosides. The acidic mucopolysaccharides, which consist of disaccharide repeating units containing D-glucuronic or L-iduronic acid and glucosamine or galactosamine, respectively, are also members of the class of glycoproteins or proteoglycans. Because L-iduronic acid is not readily available it must be prepared. A new synthesis from Dglucose was recently described by formation of the exo-glucal, diastereoselective hydroboration, and oxidation of C-6 [ 108). Galactosamine is also a very expensive starting material and it has therefore been prepared from glucosamine by inversion of the configuration of the 4-OH group via the triflate, and used for the synthesis of dermatan sulfate fragments [ 1091. In another approach [ 1101 an L-idose acceptor was glycosylated stereoselectively (P: u = 2.5 : 1) with an azidogalactosyl trichloroacetimidate. The P-selectivity was achieved, without neighboring group participa-
28
2 Trichloroacetimidates
85% b
BnO
BnO
F
0
\
NPht
BF3 OEt2 CH2C12 84%
Ad)
Ad)
BF, OEt2 CH2CI2 -45% 76% Aco AcO
OAC
Aco Aco
GkNAc&l-6)
I MW(1-6)
I
GkNAcS(1-2)
1
Man~(1-4)GICNACP(1-4)GlcNA@N3
Unverzagt [102-1M]
I
GlcNAcP(l-P)Mana(l-3)
Scheme 25.
tion, in a non-polar solvent at low temperature by an SN2-type reaction. The resulting disaccharide was oxidized to the iduronic acid derivative and converted into the GalNp( 1 -4)IdoA trichloroacetimidate and into a corresponding acceptor which were then used for the next glycosylation step to provide a dermatan tetrasaccharide fragment; thus, because of neighboring group participation an a-glycosidic bond was formed stereospecifically. The tetra-, hexa-, and octasaccharide fragments of hyaluronic acid (Scheme 27) [ 1111 have been prepared by repeated glycosylation of a GlcNP( 1 -4)GlcA acceptor with a disaccharide trichloroacetimidate which was prepared from a trichloroacetyl
29
2.3 0-Glycosides
ACO AcO OBn
I
TMSOTf CH2C12,hexane 93%
Et20,-4OOC
68%
Bu~N'NO,
I
GlcNAc~(l-4)Man~(l-4)GlcNAc~(1-4)GlcNAc
I
Ga@(1-4)GlcNA1:b(1-2)Mana(1-3) Weiler, Schmidt 1531
Scheme 26.
(TCA)-protected glucosamine trichloroacetimidate and a glucuronic acid acceptor. All reactions gave, because of neighboring group participation, exclusively pglycosides in high yields. Some chondroitin fragments have been prepared starting from an azidoglucosyl trichloroacetimidate and a glucose acceptor (Scheme 28) [ 1 12, 1131. Despite the use of a non-participating neighboring group, the p-glycoside was obtained exclusively because in a non-polar solvent at low temperature with boron trifluoride as the catalyst an S,z-type reaction was favored. With trimethylsilyl triflate lower stereoselectivity (p :CI = 2 : 1) was observed. The disaccharide was oxidized to the glucuronic acid derivative and converted into the
30
2 Trichloroacetimidates
+
PhT-+
Ho* BzO
OMP
TCANH
OBz
O Y N H dCl,
q
89%
~
~
~
&
O
M
~
HO
TCANH
COOMe
-4 87%
Ph
TMSOTf
zqsy-;*oMe TCANH
Cm+ie
TCANH
COOMe
n=
hyaluronic acid
Blatter, Jaquinet
1,2,3
I1 111
Scheme 27.
GalNAc(1-4)GlcA trichloroacetimidate and the corresponding acceptor which were used again for glycosylation to yield a tetrasaccharide fragment. The di- and tetrasaccharide trichloroacetimidates were used for the glycosylation of a Galf3(13)Galf3(1-4)Xyl acceptor which represents a typical linkage of mucopolysaccharides to proteins. The resulting penta- and heptasaccharide trichloroacetimidates were used for the glycosylation of serine to yield chondroitin fragments with one or two repeating units; these compounds are of interest as acceptors for glycosyltransferases in enzymatic studies. Great biological interest has been shown in heparan sulfate or analogs of heparin, containing glucosamine and D-glucuronic or L-iduronic acid. A convergent synthesis has been reported (Scheme 29) [114], starting from an azidoglucose acceptor which was glycosylated with two iduronic acid trichloroacetimidates. The resulting two disaccharides were converted into the trichloroacetimidates and used consecutively for glycosylation of the suitably protected iduronic acid acceptor. Both aglycosidic bonds were formed stereospecifically with inversion of the configuration. Thus, a heparan trisulfate fragment has been prepared and used for binding studies to fibroblast growth factor-2. Syntheses of C-bridged heparan sulfate analogs [ 1151 and of heparin-like glycoconjugates which were used for thrombin binding studies [ 116, 1171, have also been reported. The synthesis of bacterial polysaccharides is of great importance for the development of antibacterial vaccines. A terminal a( 1-2)-linked rhamnose trisaccharide
2.3 0-Glycosides
31
YPh
Ph
Ph I
P' h
BF3.OEtz toluene. -5OOC
r
71%
1
5.0-70%
GalNAcP(1-4)GlcAP( n=1,2
Scheme 28.
HNFmoc
1-3)GalP(1-4)XylP(1 -0)Ser chondroitin
Ogawa et al. 1112,1131
32
2 Trichloroacetimidates
~
'
"
not reported
3
I
Lea
qn%
Lev0
OAc
w
HO
KCci3 84% TBDMSOTf NH
OAc
HO
I
OAll
toluene, -20°C
TBDMSOTf CHZCI,, -2OOC
IdoAa(l-4)GlcNa(l-4)ldoAa(i-4)GlcNa(l-4)IdoAal-OMe
6 0 , '
Sinay et al. [I141
Ao3Q
Scheme 29.
of the group B Streptococcus antigen has been synthesized with a 2-0-acetyl protected rhamnosyl trichloroacetimidate by repeated glycosylation and deprotection of, the 2-OH group [118]. A hexasaccharide fragment of the a(l-4)-linked 3-0methylmannose polysaccharide of Mycobacterium smegmatis has been convergently prepared, via a disaccharide building block [ 1191. From a 4-0-acetyl protected 3-0methylmannosyl trichloroacetimidate and a suitable acceptor a 3-0-methylmannose disaccharide was prepared which was converted into the trichloroacetimidate and used for repeated glycosylation and then deprotection of the 4'-OH group. All glycosidic bonds were stereospecifically formed owing to the participation of neighboring groups. Most bacterial polysaccharides are much more complex. Ninety 90 serotypes of Streptococcus pneumoniae are already known. The synthesis of a pyruvated tetrasaccharide repeating unit of Streptococcus pneumoniae type 27 has been described (Scheme 30) [ 1201. The disaccharide trichloroacetimidate donor was prepared from acetobromoglucose and the pyruvated glucosamine acceptor applying the KoenigsKnorr method. The a-linked disaccharide acceptor was prepared from a galactosyl trichloroacetimidate and a rhamnose acceptor. The use of a strong Lewis acid and solvent (diethylether) favoring an S,I -type reaction mechanism, gave the a-glycoside with high selectivity (a: = 9 : 1). Glycosylation of the disaccharide acceptor with the disaccharide trichloroacetimidate gave the tetrasaccharide repeating unit carrying a spacer which is suitable for the preparation of glycoconjugates. The syntheses of another tetrasaccharide repeating unit of this type [121] and four tetrasaccharide repeating units of Streptococcus pneumoniae type 6B [ 1221 have also been reported. The chemoenzymatic synthesis of a decasaccharide consisting of two repeating units of Streptococcus capsular polysaccharides type I11 group B (GBSP 111) (Scheme 31) [123] has been described. Glycosylation by the Koenigs-Knorr method of a 3,4-
a
2.3 0-Glycosides
61Yo
33
TMSOTf
6OoC
scheme 30.
di-O-unprotected glucosamine acceptor with acetobromogalactose gave regiospecifically the lactosamine disaccharide which was converted into an acceptor and into a trichloroacetimidate donor. Glycosylation of the disaccharide acceptor with acetobromoglucose, again under Koenigs-Knorr conditions, gave the trisaccharide building block which was transformed into the trichloroacetimidate donor. The disaccharide trichloroacetimidate was used for the glycosylation of a galactose acceptor; the resulting linear trisaccharide was glycosylated with a lactosyl trichloroacetimidate to give the pentasaccharide building block. Glycosylation with the trisaccharide trichloroacetimidate finally gave the desired octasaccharide. All pglycosidic bonds were formed stereospecifically, but the synthesis seems not to be straightforward because the tetrasaccharide repeating unit was not used twice as a building block. Finally, the neuraminic acid residues were enzymatically attached with a(2-3)sialyltransferase to yield the desired decasaccharide fragment. The synthesis of an octasaccharide mimic of two repeating units of the Streptococcus capsular polysaccharide type I11 group B (GBSP 111) with S-1-carboxyethyl groups replacing the siailic acids has also been reported [124]. A convergent synthesis has been reported for a hexasaccharide fragment of the Streptococcus group A cell-wall polysaccharide (Scheme 32) [ 1251. The 3 - 0 unprotected rhamnose acceptor was first glycosylated with the N-phthaloylprotected glucosamine trichloroacetimidate and then with a suitably protected
34
2 Trichloroucetimidutes
ACO
HS(CN12 tol. CHsNO2,
ACO
OSE
72%
.A;&oHg
OSE
Pht
NPhth
OAc
A
disaccharide acceptor
disaccharide imidate
J
-OAc
Ad)
Oh43
TMSOTf
Glc~(1-6)GlcNAc~(1-3)Gal~(l-4)Glc~(1 -6)GlcNAcP(1-3)GalPl-OMe
I
I
GaiP(1-4)
GalP(1-4)
1
a(2-3)sialyNransferase CMP-NedAc
Glc~(l-6)GlcNAc~(l-3)Gal~(l-4)Glc~(l-6)GlcNAc~(l-3)Gal~l-OMe
I
NeuAca(2-3)GalB(l-4)
I
NeuAca(2S)Ga@(1-4)
GBSP 111 Jennings et al. [I231
Scheme 31.
rhamnosyl trichloroacetimidate. The resulting trisaccharide was converted into the trichloroacetimidate and into an acceptor; coupling yielded the hexasaccharide with high stereoselectivity. A participating neighboring group is not necessary for the formation of the a-rhamnoside bond. An efficient synthesis has also been reported for the hexadecasaccharide fragment
35
2.3 0-Glycosides OAll
B
z
O
H
TESOTf CH2CI2, -75OC 58%
r
I '
Bz
OAc
trisaccharide imidate
Rhaa(l-2)Rhaa(1-3)-Rhaa(l-2)Rha GlcNAcp(1-3)
OBz
BZO
CH2CI2, TESOTf,-75OC 84%
TESOTf, CH2C12, r.t. 43%
GlcNAcp(1-3)
trisaccharide acceptor Pinto et al. [125]
Scheme 32.
of the Shigelln dysenteria type-1 0-specific polysaccharide (Scheme 33) [ 126, 1271. For the synthesis of the tetrasaccharide repeating unit by subsequent glycosylation of the rhamnose acceptor with azidoglucosyl chloride, methylthio galactoside, and rhamnosyl trichloroacetimidate, several glycosylation methods were applied. For the ensuing gl ycosylations with the tetrasaccharide as donor, the trichloroacetimidate method was favored. Repetitive glycosylation of the hexanoic acid acceptor gave the octa-, dodeca-, and hexadecasaccharides in high yields. Coupling with the linker to human serumalbumin (HSA) enabled the preparation of materials for vaccine studies. Further oligosaccharide fragments of the Rhizobium leguminosarum [ 128, 1291, CCI, CCI,
OANH N, SPh BnO
I
AgOTf DBMP CH&12, O°C
64%
OMBn I
I
MeOTf DBMP Et20, r.1. 58%
Brio
ClAcd
BF .OH
bez b
cH3c12,200c 8940
Rhaa(1-2)Gala(l-3)GlcNAca(l-3)Rhaa 1-O(CH,),COOMe n = 2-4
BnO
OAC
HO(CH,),COOMe
Pozsgay [126,1271
Scheme 33.
36
2 Trichloroacetimidates
BnO
OH
OBn
dBn B
n
En0 O q
68%1Sn(OTI)Z Et20/CH2CI,. r.t.
+
CCI,
Sn(OTI), Et20/CH2C12,r.t.
+
En0 B
n
O
g
0 OBn
I D-Gala(1-1)-D-rnyo-inositol
(Galactinol)
Mayer, Schmidt [ 1 1
Scheme 34.
Mycobacterium gornoae [ 1301, Mycobacterium arium [ 1311, and Vibrio cholerae [ 1321 polysaccharides have also been prepared with the help of trichloroacetimidates as glycosyl donors.
2.3.2 Inositol Glycosides The synthesis of galactinol gala( 1-l)-~-myo-inositol]which is involved in the biosynthesis of the raffinose family, has been reported (Scheme 34) [133]. The readily available L-myo-inositol derivative was glycosylated with the 0-benzyl protected galactosyl trichloroacetimidate. Because of reaction conditions favoring an S,I -type reaction mechanism, the a-glycoside was formed exclusively. In the same way D-Gala(1-1)-D-myo-inositol was obtained from the corresponding D-myoinositol derivative. The glycosylphosphatidyl inositols (GPIs) are an interesting class of compounds which serve as anchors for proteins and glycoproteins in membranes. They consist of many variants in the carbohydrate moiety and in the lipid part. The first total synthesis of a GPI anchor from yeast has been reported; it contains a ceramide residue with a phytosphingosine constituent (Scheme 35) [ 134, 1351. The synthesis has been performed in a convergent manner by glycosylation of 6-0-unprotected Dmyo-inositol acceptor with the azidoglucosyl trichloroacetimidate yielding stereospecifically the a-glycoside as a result of s,~-type reaction conditions. A similar
37
2.3 0-Glycosides
BBilOn 0
0
OAll
O-(-)-Mnt
"
G
TMSOTf
NH
o&.~~,
85% Et,O. r.t.
Pl
0
BnO
TMSOTf
00
;;oq I
uoo~OyO(-)-Mnt 0
cc13
TMSOTf
O YCCI, NH
HO
"YNH CCI,
HN
0
08 0- 6Mana(1-P)Mana(1 -P)Mana(l-4)GlcNa(1-6)lnositol-l-o,
H,Nlco':/-
I
0
Mana(l-2)
8
OH
Schmidt et al. 1134,1351
Scheme 35.
approach with a benzyl-protected azidoglucosyl trichloroacetimidate in dichloromethane gave much lower stereoselectivity [ 1361. The mannose tetrasaccharide building block was prepared by the consecutive glycosylation of the 6-0-unprotected mannose acceptor with three suitably protected O-mannosyl trichloroacetimidates. The two building blocks were coupled by glycosylation of the GlcNyx(1-1)inositol acceptor with the tetramannosyl trichloroacetimidate in very good yield. All a-
38
2 Trichloroacetimidates
mannoside bonds were stereospecifically formed. The synthesis was completed by attaching the phosphate and the ceramide phosphate moieties at the suitably deprotected positions. Other inositolglycans are of pharmaceutical interest because of their insulin-like effect. The synthesis of a 0-linked inositol glycoside using a linear strategy has been reported [ 1371. The azidoglucose acceptor was first glycosylated with mannosyl trichloroacetimidate. The resulting disaccharide was again converted into the trichloroacetimidate and used for the glycosylation of the inositol acceptor. The pseudotrisaccharide was stereoselectively (p :a = 3 : 1) obtained and then consecutively glycosylated with the three suitably protected mannosyl trichloroacetimidates. Introduction of the phosphate groups gave the desired inositolglycans; some related derivatives have also been synthesized.
2.3.3 Glycosylation of Sphingosine Derivatives and Mimics The azidosphingosine glycosylation method [ 138, 1391 is well established. It has been found that azidosphingosine is a better glycosyl acceptor than ceramide or other sphingosine derivatives. Some examples of the synthesis of glycosphingolipids with complex oligosaccharide trichloroacetimidates and azidosphingosine have already been shown (see above). Even when other glycosylation methods have been used for the synthesis of the oligosaccharide moiety, the trichloroacetimidate method has been preferentially chosen for the coupling to azidosphingosine (Scheme 36) [140]. A tetrasaccharide trichloroacetimidate of the ganglio series containing three neuraminic acid residues was used for the glycosylation of 3-0-protected azidosphingosine. Reduction of azide, attachment of the fatty acid, and deprotection
N.
TMSOTf CH,CI,. O°C 65%
I NeuAca(2-8)NeuAca(2-3)
Scheme 36.
OTBDPS
I
NeuAca(2-3)
GT'a
Hasegawa et al. [14W
2.3 0-Glycosidrs
6BZ
39
Higuchi et al. [154]
Scheme 37.
yielded the ganglioside GT1,. With the help of the azidosphingosine glycosylation method many other glycosphingolipids have been synthesized, ie. GD1, [ 1401, GD2 [141], GT3 [142], GT4 [142], GQlb [143, 1441, GQlba [145], sialylated globosides [ 1461, sulfated glucuronyl paraglobosides [ 1471, sulfated sLeX glycosphingolipids [ 1481, ganglioside lactams corresponding to G M I , GM2, GM3, and GM4 [ 1491, and some xylose analogs of glycosphingolipids [ 1501. Although the glycosylation of ceramides has been found to proceed with low yields [ 151, 1521, this method has been applied a few times, especially when special ceramide derivatives are required and their azido derivatives were not available (Scheme 37). ‘The synthesis of astrocerebroside A, which has been isolated from starfish and which is of interest because of its pharmacological activity, has been reported via glycosylation of its ceramide moiety with 0-glucosyl trichloroacetimidate [153]. A hematoside-type ganglioside called GAA-6 which has been also found in starfish, was prepared in the same way via glycosylation of the phytosphingosine derivative with the trisaccharide trichloroacetimidate [ 1541. To find potent selectin binding inhibitors, mimics not only of the carbohydrate part of glycosphingolipids, especially of LeXand sLeX(see above), but also mimics of various lipid analogs have been prepared. 2-Tetradecylhexadecanol has been proposed as lipid moiety, and was glycosylated with the sialylated lactosyl trichloroacetimidate to yield the GM3 analogous neoglycolipid [ 1551. With the same lipid moiety were also prepared the GM4 [155], LeX[156], 3’-C-carboxymethyl LeX [ 1571, and some sulfated [ 158- 1601 and phosphorylated [ 1601 neoglycolipids. Another lipid moiety containing a spacer of variable length was glycosylated with the required trichloroacetimidate to prepare sLeXneoglycolipids [ 1611. A double-chain bis-sulfone has been used for the glycosylation with the corresponding trichloroacetimidates in the synthesis of a globotriosyl neoglycolipid and some deoxy derivatives [162, 1631. Other lipid moieties have been used for various purposes (Scheme 38). The hexadecanediol derivative was glycosylated with the trisaccharide trichloroacetimidate [ 1641. The resulting glycoside was transformed into the 16-mercaptohexadecanyl glycoside and used for biosensor studies. Glycosylation of a trivalent acceptor with mannosyl trichloroacetimidate furnished a triantennary cluster mannoside; its
2 Trichloroucetimidutes
40
TMSOTf CH2C12,r.t. 71%
1 \OAc
AcO
?Oq
no
0
NH +
Y CCI,
TMSOTf CH2C12, -65°C b 74%
HO$
no
Lindhorst et al. 11651
+
m 2 w p e x a n e , r.t.
no
~
49-72%
-OH
*R
Schmidt et al. [1661
Scheme 38.
binding properties to lectins were investigated [ 1651. Long-chain diols were glycosylated with glucosyl trichloroacetimidate to synthesize bis-glycosides, furnishing new types of non-ionic surfactants of the 2/1-type (two sugar head groups, one lipophilic chain) [ 1661. Surfactants of the 2/2-type have also been prepared [ 1661. 2.3.4 Glycosylation of Amino Acids The well established method [167] for the preparation of a-glycosylated serine and threonine derivatives has also been applied to the attachment of complex oligosaccharides (Scheme 39). Glycosylation of the serine acceptor with the P-configured trisaccharide trichloroacetimidate gave the a-glycosylated product stereospecifically, thus furnishing a derivative of the Fla-antigen [ 1681. Other derivatives including the sialyl T (ST) tumor antigen [ 1691, have also been prepared. The use of N-acetyl-protected and 4,6-O-benzylidene-protectedgalactosamine trichloroacetimidates has been proposed for the synthesis of a-glycosides [170]. Because the cisbicyclic structure disfavors oxazoline formation, a-glycosides are formed exclusively even from the a-trichloroacetimidates. Thus the Thomsen-Friedenreich (TF) antigen has been prepared from the Galp( 1-3)GalNAc trichloroacetimidate and serine or threonine as acceptor [ 1711.
2.3 0-Glycosides
41
HNFmoc HO
GalP(1-4)GlcNP(l-G)GalNa(1-3)Ser
Danishefsky et al. [I681 NH
Ph HNFmoc HO . hCOOCH,COPh
BF3.0Etz,THF, -20%
Ad3
Koganti et al. [1711
68% kl,
HtjFmoc
rCm,
HO
m AGO $
R = H, CH3 R' = All, Pfp
R
TMSOTf, CH2CIz,r.t.
TeocN
HNAc
80-90% HoYNH CCI,
Saha, Schmidt 11721
k0% AcO
Ad3
TMSOTf, CHzCIz, 74%
b
I O YCCI, N H
'
O
H
% A +
DtsN
Fmoc-lle-Ser-Gly-lle-Gly- OCH,
A
Fmoc-lle-S~r-Gly-Ile-Gly
I
I
TMSOTf, CH2CI2, 78%
G Resin e +
A%$
0
I
O YCCI, N H
MeMal et a1.[1731
Fmoc-Ile-Ser-Gly-lle-Gly- OCH,
Scheme 39.
The preparation of Gala(1-3)Ser and its use for further syntheses has also been reported [98, 99, 170, 1711. The N-trichloroethoxy (Teoc)-protected glucosamine trichloroacetimidate has been employed for the synthesis of P-glycosidically linked amino acids [ 1721. Glycosylation of various protected serine and threonine esters gave P-glycosides, because of the presence of participating neighboring groups. The N-tetrachlorophthaloyl (TCP)-protected derivatives have been used similarly. After conversion into the N-acetyl derivatives, the building blocks are suitable for glycopeptide synthesis. A completely different approach for the synthesis of glycopeptides has been reported by glycosylation of the serine-containing peptides on the solid-phase [ 1731. A polyoxypropylene cross-linked polyethylene glycol resin (POEPOP, polyoxyethylene-polyoxypropylene) was chosen because it contains only ether bonds and no amide bonds, and several linkers were investigated. The use of an Ndithiasuccinyl (Dts)-protected glucosamine trichloroacetimidate as donor gave the P-glycosylated peptide whereas the use of the azidoglucosyl trichloroacetimidate
42
2 Trichloroacetimidates
gave, as expected, the a-glycosylated peptide. Galactosyl, mannosyl, and fucosyl trichloroacetimidates have been used for the synthesis of libraries of peptide acceptors with more than one serine residue. 2.3.5 Polycyclic and Macrocyclic Glycosides Glycosides of polycycles or macrocycles (anthracyclines, chalicheamicin, macrolactones, etc.) are of great interest because of their antibiotic and antitumor activity. The synthesis of calichearubicin A and B, which have the same carbohydrate moiety as calicheamicin, has recently been reported (Scheme 40) [174, 1751. The phenolic acceptor was stereospecifically glycosylated with rhamnosyl trichloroacetimidate in very good yield. The resulting a-glycoside was transformed into the trichloroacetimidate donor which was used for the glycosylation of the anthracycline acceptor with silver triflate as catalyst. The a-glycosidically linked calichearubicin A was stereoselectively ( a :P = 5 : 1) obtained. The P-glycosidically linked calichearubicin B was similarly prepared from the same trichloroacetimidate donor with boron trifluoride-diethyl ether as the catalyst and, despite the lack of a participating neighboring group, again the P-stereoselectivitywas high (P : a = 5 : 1, 35%). The syntheses of a modified carbohydrate moiety, a head-to-tail dimer of the calicheamicin oligosaccharide [ 1761, the 1,1'-disaccharide (trehalose) containing the carbohydrate moiety of everninomycin [ 1771, and the vancomycin disaccharide CH,
BF,.OEtz H " ; iTBDMGH3 ; ; . CH30
+
HO
OAc
OCH,
OCH,
CH2CI2 95%
OCH,
OCH,
TBDMSO
0%
\/ ?
H,CO
CU
OCH,
H:q Danishefsky et al. [174,1751
CH30
OH
OH
calichearubicinA
Scheme 40.
HO
a
43
2.3 0-Glycosides OTESMo
0
TMSOTf dioxaneflol., O'C 75% (a$=8:1)
OH
+
CCI,
HNWoOPMB b o T B D M s I
Nicolaou et al. [181,1821
OTBDMS
TMSOTf CH2CI , -78'C 91 % (i:a=5:1)
eleutherobin
OH
TMSOTf CH2CI2, -4O'C not reported F CCI,
C I A c O ) TBDMSO PhS
iPrC0
M &
HO
I
Me0
v
'Me
OH OH
HO
HO HO &
o
o
0
u iPrC0
iPrCO O L *k
OH OH
olivomycin A
Roush et al. [1831
Scheme 41.
[ 1781 have also been reported. The total synthesis of neocarcinostatin including the preparation of the N-methylfucosamine trichloroacetimidate and the glycosylation of the endiyne-type aglycone were recently described [ 179, 1801. The synthesis of eleutherobin, which has antitumor activity and cytotoxic properties similar to those of taxol, has also been reported (Scheme 41) [181, 1821. The carvone-derived acceptor was stereoselectively glycosylated with the arabinosyl trichloroacetimidate ( a :p = 8: 1). The resulting glycoside intermediate was treated as for sarcodictyins A and B to yield eleutherobin and eleuthosides A and B. Studies of the synthesis of olivomycin A have been reported [ 1831. Glycosylation of a glycal acceptor with a trichloroacetimidate and an acetate donor gave a trisaccharide which was transformed into the trichloroacetimidate and used for the glycosylation of the acyloin acceptor. The resulting P-glycoside is a model compound for the approach to the synthesis of olivomycin A.
44
2 Trichloroacetimidates
OH
80% (1:1)
I
BFa.OEt2 CH2C123 -80c
no
Jiang, Schmidt [184,1851
calonyctinA
Scheme 42.
The macrolactone calonyctin A, a plant growth regulator, has been synthesized (Scheme 42) [ 184, 18.51. The quinovose acceptor was glycosylated subsequently with the suitably protected quinovosyl, rhamnosyl, and quinovosyl trichloroacetimidates; all steps could be performed stereospecifically. Transformation of the tetrasaccharide into the trichloroacetimidate and glycosylation of the racemic hydroxy acid derivative gave two epimeric compounds. Separation and lactonization gave calonyctin A. A convergent strategy has been applied to the synthesis of Tricolorin A, a natural herbicide with cytotoxic activity against cultured P-388 and human breast cancer cells (Scheme 43) [186, 1871. The acceptor was prepared by glycosylation of the hydroxy acid derivative with the galactosyl and the glucosyl trichloroacetimidates. It was coupled with the disaccharide trichloroacetimidate which had been prepared before from the suitable rhamnose donor and acceptor. All steps proceeded with high stereoselectivity. The resulting tetrasaccharide was transformed into the macrolactone Tricolorin A. The synthesis of the disaccharide macrolactone lonitoside 1 has also been reported [ 1881. 2.3.6 Glycosides of Phosphoric and Carboxylic Acids
Trichloroacetimidates can be used for glycosylation of phosphoric and carboxylic acids without additional Lewis acid. Reaction of the fucosyl a-trichloroacetimidate
45
2.3 0-Glycosides TMSOTf CH,C12, r, t. 79%
AgOTf CH2C12,r. t. a4%
phT& PivO
0
A"Oo CCI,
YNH CCI,
CCI,
0
TMSOTf CH2C12,r.t. 75%
BnO
OBn
0 0
0
HO
Hd Larsson, Heathcock [186,1871
tricolorin A
Scheme 43.
with dibenzyl phosphate gave the b-fucosyl phosphate with stereospecific inversion of configuraticin (Scheme 44) [189]. Deprotection and coupling with GMP morpholidate yielded GMP fucose which was purified by preparative HPLC. Reaction of the galactosyl trichloroacetimidate with a uridine phosphonate derivative furnished a phosphonate analog of UDP-galactose [22] which might serve as glycosyl donor or as inhibitor for galactosyltransferases. Some nucleoside monophosphate sugars have also been prepared directly by reaction of 0-glycosyl trichloroacetimidates with nucleoside monophosphates [ 1901. Reaction of the glucosyl trichloroacetimidate with a ceramide- 1-phosphate derivative gave exclusively the P-glycoside, owing to the participating neighboring group [ 1911. Reaction of the benzyl-protected glucosyl P-trichloroacetimidate with a malonic acid derivative as acceptor gave, with inversion of configuration, the a-linked malonyl derivative which was designed to mimic the pyrophosphate moiety of UDP-glucose and to serve as inhibitor for glycosyltransferases [ 1921. 2.3.7 Solid-Phase Synthesis
Although solid-phase chemistry is well developed, progress has not yet been fully extended to oligosaccharide chemistry, because of the high demands on the polymer support and the lack of powerful analytical tools for monitoring reactions on solid phases. The synthesis of an a(1-2)-linked pentamannose moiety has recently been reported (Scheme 45) [193]; a Merrifield resin, a thio-linker, and a 2-0-acetyl protected mannosyl trichloroacetimidate were used. The glycosylation reaction was
46
2 Trichloroucetimidutes CCI,
0
Schmidt et al. [IS91 0 A*
OAc
AcO!&&oyCCI, OAC
0
0
II
+
NH
Schrnelzer 1221
HO AcO
OAc
Schmidt et al. [I911
CCI,
It II Wong et al. [I921
x
0
0
HO
OH
Scheme 44.
monitored by MALDI-TOF and, after oxidative cleavage from the solid phase, the oligosaccharide was obtained by preparative HPLC. The method described has been applied to other examples, i.e. the synthesis of the branched-core pentasaccharide moiety of complex type N-glycans [ 194, 1951. The same 2-0-acetyl-protected mannosyl trichloroacetimidate was used in a polymer-supported solution-phase synthesis of a tetramannose moiety with polyethylene glycol monomethyl ether (MPEG) as polymer-support [ 1961. The use of controlled-pore glass (CPG) as solid-phase support is under investigation in the synthesis of oligosaccharides [ 1971 and glyconucleotide conjugates [ 1981 with trichloroacetimidates as donors. The synthesis of polylactosamine oligosaccharides was performed with a Merrifield resin and a benzyl-type linker (Scheme 46) [199].The glycosylation was stereospecifically performed with a phthalimido-protected lactosamine trichloroacetimidate bearing a levulinoyl group as temporary protecting group which can be removed with hydrazinium acetate under mild conditions. After cleavage from the linker the octasaccharide was obtained in good yield (overall 42%).
47
2.3 Q-Glycosides r
1
bR
Rademann, Schmidt [I931
R = H, CH,
Scheme 45.
Heparan sulfate-like oligomers have been prepared by polyethylene glycol monomethyl ether (MPEG)-supported solution-phase synthesis (Scheme 47) [200]. Glycosylation of the succinyl linked acceptor (linkage not via the anomeric position) was performed with the disaccharide trichloroacetimidate up to five times, again using the levulinoyl group as temporary protecting group. The yield of the coupling step could be increased to 95% by optimizing the reaction temperature to 10 "C, and only the a-glycoside was obtained. Cleavage from the linker with lithium hydro-
,
Ph,hN
OAC
BnO
,
,
~ BnO
~
~
o
NH
A
C
C
~
NH,NH,.AcOH EtOH
,
OHn
1
TrtBF,
CH,CI,.
En0
OBn
OBn
r.t.
Ogawa et al. 11991 n = 1-3
Scheme 46.
48
2 Trichloroacetimidates
OMe
Dreef-Tromp et al. I2001
n = 2-5
Scheme 47.
peroxide and further transformations yielded the hexa-, octa-, deca-, and dodecasaccharide fragments of heparan sulfate. In a recently introduced method for the synthesis of glycopeptides the peptide was synthesized from monoglycosylated amino acid derivatives followed by glycosylation reactions on the same solid phase (Scheme 48) [201]. A polyethylene glycol N,N-dimethylacrylamide copolymer (PEGA) resin was used for the synthesis of the nonapeptide acceptor. When the resin-bound acceptor was thoroughly washed and dried before subsequent glycosylation with the benzoyl-protected trichloroacetimidate, the core 3 peptide derivative was stereospecifically obtained in good yield (62%). The synthesis of a-glycosides with trichloroacetimidates bearing no participating neighboring groups is much more difficult. The reactivity of the donor has to be well adapted. Nevertheless, glycosylation of the octapeptide acceptor with the benzoyl-protected azidogalactosyl trichloroacetimidate was stereospecific, but gave the core 5 peptide derivative in only 20% yield. Use of the corresponding less reactive 0-acetyl-protected trichloroacetimidate did not work. Further examples employed disaccharide trichloroacetimidates or performed two subsequent glycosylations to synthesize branched trisaccharides. Although the direct glycosylation of OH-unprotected serine-containing peptides did not work on this resin, the use of another resin, containing no amide bonds, gave good results (see above, Scheme 39) 11731. Further applications of polymer-supported glycosylations for the synthesis of
2.4 S-Glycosides
49
Ph ,002
I
Ac-Glu-Pro-Thr-Thr-Thr-Pro-lle-Thr-Thr7 Ac-Glu-Pro-Thr-Thr-Thr-Pro-lle-Thr-Thr-
I
‘Bu
l
‘Bu
l
‘Bu
I I
‘Bu ‘Bu
Ac H Resin
CH&
AcN H i
“I3 TMSOTf “I3
b Ac-Glu-Pro-Thr-Thr-Thr-Pro-Ile-Thr-Thr-NH2
-15OC
core 3
62%
*
TMSOTf CH2CI2, -1 5OC 20%
Ac-Pro-Thr-Thr-Thr-Pro-Ile-Thr-Thr-NH,
core 5
Bock et al. iZOl1
Scheme 48.
oligosaccharide libraries by a combinatorial approach have been reported; to this end, polymer-bound acceptors with several free hydroxy groups were glycosylated randomly with trichloroacetimidates [2021.
2.4 S-Glycosides Thio-linked analogs of oligosaccharides, i. e. Lewis’, sialyl Lewis’, etc., are of interest because of their improved stability to glycosidases. The synthesis of several examples by the trichloroacetimidate glycosylation method has been described (Scheme 49) [204, 2051. Glycosylation of the 3-thio galactose acceptor with a fucosyl trichloroacctimidate gave the a-disaccharide stereospecifically; this was converted into the 3,4-dithio glucose derivative via the triflate and then substitution with inversion of the configuration. Conversion into the disaccharide trichloroacetimidate and glycosylation of heptyl mercaptan gave the thio-linked disaccharide acceptor which was coupled with the neuraminic acid disaccharide to yield the sLeX analog containing only thio linkages and a glucose instead of a glucosamine moiety. For synthesis of the LeXanalog, the disaccharide intermediate was coupled with acetobromogalactose and transformed into the trisaccharide trichloroacetimidate. Glycosylation of the thio-linked acceptor, which was prepared from the lactosyl trichloroacetimidate and heptyl mercaptan, yielded the Le’ analogdus pentasaccharide. All p-glycosidic bonds were stereospecifically formed owing to the participation of neighboring groups. Similarly the thio-linked Lewisa [205]and ganglioside GM3 [206] epitopes have been prepared.
50
2 Trichloroucetimidutes
OH OH HO
LeXanabg
Eisele, Schmidt I2031
Scheme 49.
The benzyl-protected mannosyl a-trichloroacetimidate has been used for the glycosylation of 2-mercaptopyridine (Scheme 50) [207], but the stereoselectivity was low. The P-glycoside was separated and oxidized to the 2-pyridyl sulfone which was employed as glycosyl donor for the synthesis of C-glycosides. The corresponding azidogalactose and N-acetylgalactosamine derivatives have also been prepared [208]. An S-glycosylated amino acid derivative has been synthesized by glycosylation of a D-cysteine derivative with the L-rhamnosyl trichloroacetimidate [209]. The Sglycosyl amino acid was used for the synthesis of an 5'-glycopeptide derivative of a luteinizing hormone-releasing hormone (LH-RH) antagonist. The S-glucosylated L-
2.6 C-Glycosides
51
(pa= 5:4) Beau et al. 12071
CCI,
c
HS
50%
c
Kessler et al. [2091
Scheme 50.
cysteine has been prepared applying the same method [210]. Some glycosylations of thiophenol [21 I ] and thiobenzyl alcohol [212]derivatives with trichloroacetimidates have also been reported.
2.5 N- and P-Glycosides Trichloroacetimidates are also suitable glycosyl donors for the synthesis of Nglycosides. For instance, reaction of N-phthaloyl-protected glucosamine trichloroacetimidate with trimethylsilyl azide gave, owing to neighboring group participation, only the p-glycosyl azide (Scheme 51) [213]. In the synthesis of Nglycopeptides the glucosamine azide is a suitable building block at the reducing end. After reduction of the azide to the amino group it can be linked to aspartate via amide bond formation. Another example of the synthesis of N-glycosides is the reaction of the ribopyranosyl trichloroacetimidate with 2-(3-pyrazolyl)pyridine [2141. The resulting nucleotide was employed for investigations on non-helical supramolecular nanosystems. A P-glycoside has been prepared with the hemiacetal-type trichloroacetimidate and trimethyl phosphite [2151. The resulting diastereomeric phosphonates can be considered as P-analogs of uronic acids, and their glycosides are of interest in investigations with glycosidases.
2.6 C-Glycosides Application of trichloroacetimidates to the synthesis of aromatic C-glycosides, i. e. vitexin, isovitexin, isoembigenin, etc. which are of interest because ot their physiological properties, is well established [216, 2171. A furan derivative was recently
52
2 Trichloroucetimidutes
0
&lo phq *'
NPht
CCI,
KNH
TMSN3 TMSOTf, CH2CI,, -78'C) 700,"
lto et al. k131
NPht
Eschenrnoser et al. [2141 CCI,
BnLv OPWH,),
P(OCH& TMSOTf, CH3CN, 4'C 43%
BnO
w *
OAll
+
Bgo%oAl,
OAll
OPWH,),
1:l
Vasella et al. [2151
Scheme 51.
glycosylated with glucosyl trichloroacetimidate to yield the P-glycoside stereospecifically; this served as intermediate in the synthesis of visnagine analogs (Scheme 52) [218]. The synthesis of bis(C-glycosyl) compounds [219] and of glycosides with glucosamine [220] has also been reported. Occasionally the 0-glycoside intermediates could be isolated and subjected to Fries-type rearrangement to furnish the final C-glycosides. _OBn
+
O n% 'h
O Y N H
TMSOTt CH2C12,-300C,
&CH,
0
'
OH
g
EilO
77% OBn
iCI, BnO 0 n
Schmidt et al. [2181
TMSCN
Aa&o$cl, Ad)
OAc
CH2C12, TMSOTfr.t. qu
CN
Shiozaki et al. [222,223]
References
53
A known method [221] for the preparation of C-glycosyl cyanides from trichloroacetimidates has been applied to the reaction of the 0-acetyl-protected 0glucosyl trichloroacetimidate [222, 2231. Reaction with trimethylsilyl cyanide gave the a-glycoside, a valuable intermediate in the synthesis of carboxylic acid derivatives or other C-glycosides, in quantitative yield. The reaction of trichloroacetimidates with silylenol ethers is also well established (2211. Another interesting example, reaction of benzyl-protected galactosyl trichloroacetimidate with a silyl enol ether, which can be considered as a homoalanine carbanion equivalent [224], led to the a-glycoside; as expected from previous results [221] it was formed with high stereoselectivity. The P-glycoside could be obtained by base-catalyzed isomerization. Further transformations were performed to obtain the a- and P-C--galactosyl-L-serinederivatives.
2.7 Conclusion and Outlook 0-Glycosyl trichloroacetimidates have proven to be valuable glycosyl donors for efficient syntheses of various types of glycosides. Their ease of formation and their high glycosyl donor properties released under mild acid catalysis has led to extraordinarily wide application. Not surprisingly, 0-glycosyl trichloroacetimidates have often afforded the best results in demanding glycosylation studies. The trichloroacetimidate method will, therefore, continue to advance efficient synthesis, particularly of the complex glycoconjugates which are in demand for biological and clinical studies. Thus, the trichloroacetimidate method will also contribute strongly to the future development of glycoscience.
References 1. R. R. Schmidt, Angew. Chem. 1986, 98,213-236; Angew. Chem. Int. Ed. Engl. 1986,25, 212235. 2. R. R. Schmidt, in Stereochemistry of Organic and Bioorganic Transformation-Workshop Conferences Hoechst (W. Bartmann, K. B. Sharpless, Eds), Vol. 17, pp 169-189, VCH, Weinheim, 1987). 3. R. R. Schmidt, Pure Appl. Chem. 1986,61, 1257-1270. 4. R. R. Schmidt in Comprehensive Organic Synthesis, Vol. 6, B. M. Trost, I. Fleming, E. Winterfeld, Eds., Pergamon Press, Oxford 1991, pp. 33-64. 5. R. R. Schmidt, in Carbohydrates-Synthetic Methods and Application in Medicinal Chemistry, A. Hasegawa, H. Ogura, T. Suamin, Eds., Kodanasha Scientific, Tokyo 1992, pp. 66-88. 6. K. Toshima, K. Tatsuta, Chem. Rev. 1993, 93, 1503-1531. 7. R. R. Schmidt, W. Kinzy, Adv. Carbohydr. Chem. Biochem. 1994, 50, 21-123. 8. R. R. Schmidt in Modern Methods in Curbohydrate Synthesis, S. H. Khan, R. A. O’Neill, Eds., Hanvood Academic Publishers, Chur, Schweiz, 1996, pp. 20-54. 9. R. R. Schmidt, K.-H. Jung in Preparative Carbohydrate Chemistry, S. Hannessian, Ed. Marcel Dekker, Inc., New York, 1997, pp. 283-312.
54
2 Trichloroacetimidates
10. R. R. Schmidt in Glycosciences: Status and Perspectives, H.-J. Gabius, S. Gabius, Eds., Chapman and Hall, Weinheim, 1997, pp. 31-53. 11. R. R. Schmidt, Pure Appl. Chem. 1998, 70, 397-402, 12. R. R. Schmidt, J. C. Castro-Palomino, 0. Retz, Pure Appl. Chem., in print. 13. F. Barresi, 0. Hindsgaul in Modern Synthetic Methods, B. Ernst, C. Leumann, Eds., Verlag Helvetica Chimica Acta, Basel, 1995, pp. 283-330. 14. R. R. Schmidt and J. Michel, Angew. Chem. 1980,92, 763-764; Angew. Chem., Znt. Ed. Engl. 1980, 19, 731-732. 15. R. Hoos, J. Huixin, A. Vasella, P. Weiss, Helo. Chim. Acta 1996, 79, 1757-1784. 16. V. J. Patil, Tetrahedron Lett. 1996, 37, 1481-1484. 17. S. P. Douglas, D. M. Whitfield, J. J. Krepinsky, J. Curbohydr. Chem. 1993, 12, 131-136. 18. G. G. Cross, D. M. Whitfield, Synlett 1998, 487-488. 19. H. Waldmann, G. Boehm, U. Schmid, H. Roettele, Angew. Chem. 1994,106,2024-2025 (See also Angew. Chem., Int. Ed. Engl., 1994,33, 1994-1996). 20. U. Schmid, H. Waldmann, Liebigs Ann.lRec1. 1997, 2573-2577. 21. A. Lubineau, B. J. Drouillat, J. Curbohydr. Chem. 1997, 16, 1179-1186. 22. U. Schmelzer, Dissertation, Universitat Konstanz, 1997. 23. U. Huchel, C. Schmidt, R. R. Schmidt, Eur. J. Org. Chem. 1998, 1353-1360. 24. A. Lubineau, K. Basset-Carpentier, C. Auge, Curbohydr. Res. 1997, 300, 161-167. 25. H. Paulsen, S. Peters, T. Bielfeldt, M. Meldal, K. Bock, Curbohydr. Res. 1995, 268, 17-34. 26. M.-Z. Liu, H.-N. Fan, Z.-W. Guo, Y.-Z. Hui, J. Carbohydr. Chem. 1996,15, 1139-1145. 27. T. Tsuda, S.-I. Nishimura, Chem. Commun. (Cambridge) 1996, 2779-2780. 28. J. A. L. M. van Dorst, C. J. van Heusden, A. F. Voskamp, J. P. Kamerling, J. F. G. Vliegenthart, Carbohydr. Res. 1996,291, 63-83. 29. T. Nishimura, F. Nakatsubo, Carbohydr. Res. 1996, 294, 53-64. 30. G. Limberg, G. C. Slim, C. A. Compston, P. Stangier, M. M. Palcic, R. H. Furneaux, Liebigs Ann. 1996, 1773-1784. 31. Ch. Li, B. Yu, M. Liu, Y. Hui, Curbohydr. Res. 1998, 306, 189-195. 32. S. Deng, B. Yu, Y. Hui, Tetrahedron Lett. 1998, 39, 6511-6514. 33. J. C. Castro-Palomino, R. R. Schmidt, Tetrahedron Lett. 1995,36, 5343-5346. 34. M. Lergenmuller, Y. Ito, T. Ogawa, Tetruhedron 1998, 54, 1381-1394. 35. H. Paulsen, B. Halpap, Curbohydr. Res. 1991, 216, 195-212. 36. W. Dullenkopf, J. C. Castro-Palomino, L. Manzoni, R. R. Schmidt, Carbohydr. Res. 1996, 296, 135-147. 37. W.-C. Liu, M. Oikawa, K. Fukase, Y. Suda, H. Winarno, S. Mori, M. Hashimoto, S. Kusumoto, Bull. Chem. SOC.Jpn. 1997, 70, 1441-1450. 38. M. Oikawa, A. Wada, H. Yoshizaki, K. Fukase, S. Kusumoto, Bull. Chem. SOC.Jpn. 1997, 70, 1435-1440. 39. K. Fukase, Y. Fukase, M. Oikawa, W.-C. Liu, Y. Suda, S. Kusumoto, Tetrahedron 1998, 54, 4033-4050. 40. X. Qian, 0. Hindsgaul, Chem. Commun. 1997, 1059-1060. 41. S. G. Bowers, D. M. Coe, G.4. Boons, J. Org. Chem. 1998,63,4570-4571. 42. J. C. Castro-Palomino, Dissertation, Universitat Konstanz, 1998. 43. M. R. E. Aly, J. C. Castro-Palomino, El-Sayed I. Ibrahim, El-Sayed H. El-Ashry, and R. R. Schmidt, Eur. J. Org. Chem. 1998, 2305-2316. 44. E. Meinjohanns, M. Meldal, A. Schleyer, H. Paulsen, K. Bock, J. Chem. SOC.,Perkin Trans. 1 1996, 985-993. 45. G. Blatter, J.-M. Beau, J.-C. Jacquinet, Carbohydr. Res. 1994,260, 189-202. 46. R. Kosmol, L. Hennig, P. Welzel, M. Findeisen, D. Muller, A. Markus, Van J. Heijenoort, J. Prukt. Chem. Chem.-Ztg. 1997,339, 340-358. 47. 0. Ritzeler, L. Hennig, M. Findeisen, P. Welzel, D. Mueller, Tetrahedron 1997, 53, 16651674. 48. R. U. Lemieux, R. M. Ratcliffe, Can. J. Chem. 1979,54, 1244-1251. 49. A. Vasella, C. Witzig, J.-L. Chiara, Helv. Chim. Acta 1991, 74, 2073-2077. 50. I. Toth, G. Dekany, B. Kellam, PCT Znt. Appl., WO 9838197 A1 19980903, 42 pp., (Chem. Abstr., 1998, 129, 216855).
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Carbohydrates in Chemistry and Biology Beat Ernst, Gerald W. Hart, Pierre Sinay copyrightQ WILEY-VCH Verlag GmbH, 2000
3 Iterative Assembly of Glycals and Glycal Derivatives: The Synthesis of Glycosylated Natural Products and Complex Oligosaccharides Lawrence J. Williams, Robert M. Garbaccio, and Samuel J. Danishefsky
3.1 Introduction Polypeptides, oligonucleotides and oligosaccharides are three classes of oligomers that play key roles in transacting the processes of life. While the functions of proteins and DN,4 have been appreciated, at least qualitatively, for over fifty years, basic information as to the vital missions of carbohydrates, beyond that of energy storage, are still being elucidated. Thus, the roles of oligosaccharides in cellular adhesion, protein folding, cell signaling, fertilization, pathogen binding and inflammation have been recognized only recently. The detection, purification and structure determination of complex oligosaccharides have been critical in the emergence of glycobiology. The continuing maturation of this science has added to the incentives for preparing complex oligosaccharide conjugates in homogeneous form. Among these incentives is the possibility of evaluating vaccines comprised of synthetic, cell free, carbohydrate-based tumor antigens for enhancing immune response to cancers which bear such cell surface epitopes. In addition to the necessity for such homogeneous constructs, the preparation of complex oligosaccharides poses no small challenge to the science of chemical synthesis. While the successes achieved in oligonucleotide and oligopeptide synthesis arose only after long term and exacting research, the issues associated with oligosaccharide synthesis are of a much higher level of complexity. In assembling either amide bonds for polypeptide construction, or internucleotide phosphate bonds in DNA synthesis, no new stereochemical issues are encountered. By contrast, each glycosylation reaction in oligosaccharide construction involves a question of stereochemical outcome at the anomeric site (a or P-linkage, Figure 1). Moreover, every glycosylation event requires identification of a specific hydroxyl group to serve as an acceptor center (Scheme 1, A). In a typical hexose, the pinpointing of an acceptor site obliges one to identify one of the five potential hydroxyl groups to serve as the reaction locus for glycosylation. In some instances, this specificity or selectivity of action may reflect inherent reactivity margins between free
62
3 Iterative Assembly of Glycals and Glycal Derivatives
Oligopeptides
Oligonucleotides
Oligosaccharides
RO
Glycoside Bond
1-
RO RO RO
OR
Figure 1.
hydroxyl groups. Alternatively and much more commonly, oligosaccharide construction involves extensive reliance on the use of protecting group strategies. For purposes of reiteration, a specific protecting group at the reducing end of an oligosaccharide, having been brought in at the glycosyl acceptor stage, would then be converted into a donating group. In addition to the requirement for manipulating the acceptor and donor character of the terminal hexose with each elongation cycle, the need for inclusion of N-acetyl functions, as well as occasional C-methyl, 0-methyl, 0-acyl, or sulfated alcohol groups, not to speak of sialic acid units, serves to further complicate an already daunting set of challenges. It was with these considerations in mind that we began to explore the possible advantages of a new strategy, ie. glycal assembly, to facilitate oligosaccharide construction [l]. While the use of glycals as direct glycosyl donors or precursors of glycosyl donors had been practiced long before our entry to the field in 1988, it seemed that several potentially interesting and promising synthetic opportunities had not been recognized. Upon casual inspection, it appeared that the complexities associated with differential hydroxyl protection would be significantly reduced in a glycal. Thus, in a hexose glycal, only three hydroxyls need be distinguished (Scheme 1, B). Further-
3.1 Introduction
63
A
1
1
a
-
O
H _L Po
HO
--+bop :bop OP
PO
OH
+
PO
Po
OP
OP
HO
Ohgosaccharide
4
X PO
OP Po
OP
B Po
E+
PO Po
Po
Reiterate Ohgosaccharide
4
Po
Scheme 1.
more, each hyclroxyl could well differ from the others in its expected reactivity, since one is primary.,one is allylic, and the other is a more hindered secondary alcohol. It seemed, therefore, that the need for selective protection could be lessened and those protections which are needed could be simplified in the context of glycals. The most significant point of departure of ‘glycal assembly’ originated from the use of glycals as both glycosyl donors and glycosyl acceptors. This two modality
64
3 Iterative Assembly of Glycals and Glycal Derivatives
usage sets up the possibility of synthesizing polysaccharides by the assembly of glycals in an iterative fashion. In this approach, the activated, glycal-derived donor would be captured by a glycal acceptor in a glycosylation reaction (Scheme 1, B). The glycal linkage of the newly generated disaccharide, though initially introduced as a glycosyl acceptor, could now serve as a donor for the next elongation cycle. Thus, glycals would have the potential advantage that coupling maneuvers could be implemented, and reiterated, with minimal protecting group manipulation. It is well to emphasize that the success of the glycal paradigm could not have been assumed in advance of experiment. Thus, employment of a glycal-housed hydroxyl as the glycosyl acceptor means that the sensitive enol ether linkage, bearing a potential allylic leaving group at C3, must withstand the action of the promoter required for the glycosylation event. Yet, glycal linkages bearing such leaving groups are often subject to Ferrier rearrangement under conditions similar to those that would be used in glycosylation. Hence, it was necessary to find promoter conditions that were effective for glycosylation while consistent with survival of the acceptor glycal. Through the continued investigation of these ideas, we have developed a broad based approach to synthesize complex oligosaccharides, including glycosylated natural products, via glycals. In the context of specific target structures, the program has served as an incentive for exploring new issues of chemical reactivity. For the purpose of this review, the program description will be confined to examining, and demonstrating by example, the feasibility of these theorems in the context of selected total syntheses of polysaccharides and their conjugates. While there is a unified theme governing this chapter, i.e. that of fostering progression of the methodology and strategy of synthesis of complex glycans, the discussion is divided into several parts. For purposes of presentation, each of the first four sections introduces a key methodological advance in glycal technology, typically under the umbrella of the natural product that inspired them. The oligosaccharide targets discussed in the last three sections demonstrate the integrated application of these methodologies, and the iterative glycal assembly strategy, to access tumor-associated oligosaccharides used in our expanding anti-cancer vaccine program.
3.2 Ciclamycin 0 The ciclamycin complex of antibiotics possesses high inhibitory activity against experimental tumors [2] and is claimed to be of value against human neoplasia [3]. These antibiotics are largely or entirely composed of q- and 8-pyrromycinones joined at C7 by glycosidic linkages to variously permuted carbohydrate domains [4, 51. One component of this complex, which is particularly difficult to obtain, is ciclamycin 0. At the time of our investigation, the structural assignment for 1 was based solely on spectroscopic arguments. Our strategy focused on construction of an appropriately protected trisaccharide and its use as a donor to achieve glycosylation of the anthracyclinone nucleus.
3.2 Ciclamycin 0
OH 0
OH
65
P
e &eM
1 Ciclamycin 0
0
Figure 2.
Given our interest in iterative assembly, a trisaccharide glycal was envisioned to be the target. The requirement for a-linked 2-deoxy hexoses prompted the utilization of the iodoglycosylation reaction developed by Lemieux [6] and Thiem [7] (Scheme 2). Adapting this methodology to iterative glycal assembly required strict control of the roles of glycals, since substochiometric amounts of iodine could, in principle, react with either the donor glycal or the acceptor glycal resulting in coincident symmetrical coupling and possibly polymerization. It had long been known that acyl protecting groups lower the reactivity of glycosy1 donors [gal, but the idea of exploiting this effect in the coupling of two potential glycosyl donors had not been conceptualized until the seminal experiments of Fraser-Reid [Sb]. Consequently, it was hoped that the nature of such a coupling could be controlled by the resident substituents on two different glycals [9]. Glycal6 has its oxygen atoms alkylated, while those of 7 are acylated. Consistent with expectations, glycal 6 proved to be more reactive towards the iodonium electrophile, thereby generating the active glycosyl donor selectively in the presence of acceptor 7 (Scheme 3). Glycal 7 has a free hydroxyl group and, therefore, can act as the only acceptor. Iodinative coupling of 6 and 7, via trans-diaxial attack, gave rise to iodoglycoside 8 (58%). The C3 hydroxyl, allylic to the double bond of the glycal, is the most obvious position where the electronic difference between and acyloxy and an alkoxy group might be manifested. However, the clean and successful coupling of 6 and 9 to give 10 (76%) indicates that even without an acyloxy group at C3, subtle effects can be responsible for an ordered glycosylation.
2
Scheme 2.
3
4
66
3 Iterative Assembly of Glycals and Glycal Derivatives
B BnOn
O
g
+
no
O
S
/
+
O
e
b -
I+ 58%
BZos HO
6
B BnOn
O
7
6
BB n
HBZO
9
e
+
8
10
-
BZO
11
Scheme 3.
A true test for this strategy of controlling glycal-glycal coupling arrived with the total synthesis of ciclamycin 0 [lo], which embodied the additional feature of containing 2-deoxyhexoses (Scheme 4) [l 11. Coupling of benzoylated acceptor 14 to benzylated donor 13, followed by Ph3SnH reduction of the resultant iodide gave the 2-deoxy-disaccharide 15 in 57% yield. Following protecting group adjustment, silylated donor 16 was coupled to the same benzoylated acceptor 14 followed again by Ph$nH reduction, in 54% overall yield. Manipulation of the resulting trisaccharide into a suitable glycal donor was followed by a successful coupling to Epyrromycinone (19), which gave a mixture of a-linked iodides 20 in 60% overall yield. Protecting group removal and iodide reduction afforded ciclamycin 0. Up to this time, the direct coupling of an antrhacyclinone to a fully synthetic oligosaccharide en route to a naturally occurring antibiotic had not been accomplished
WI. 3.3 Allosamidin Allosamidin (21, Figure 3) was identified as a selective and powerful chitinase inhibitor in 1987 [13]. As such, it generated interest as a potential insecticide and fungicide. Allosamidin is composed of a 3,3’-epi-chitobiose P-linked to a novel aglycone sector termed ‘allosamizoline’ [ 141. This unique structure is believed to impart to it the function of a transition-state mimic for the hydrolysis of chitin [15]. The possibility that the electrophilic nature of the oxazoline linkage could allow it
3.3 Allosamidin
>
-&
67
->
OH Bno
14
13
MePo --
1. I+(symcoll)*cIo,&
2. PhaSnH, 54%
BnO 16
15
14
BnO OH 0
Mw 0
I+(symcoll)2c104-
>
19
18
20
60% M0
e
d
o
Scheme 4.
to function as a potential locus for covalent attachment to the chitin-degrading enzyme was also considered [16]. The combination of the interesting structure, valuable biological activity and scarcity in nature of allosamidin prompted our attempts at its total synthesis. In the contlext of carbohydrate synthesis, a key feature of this effort included a novel and efficient synthesis of axial glycal derivatives utilizing a Ferrier-type rearrangement [ 171 followed by a [2,3]-sigmatropic rearrangement [18, 191. The allosamidin effort also spurred development of the method of sulfonamidoglycosylation [20] for the construction of P-linked 2-aminohexoses. Following the invention and
21 Allosamidin
Figure 3.
3 Iterative Assembly of Glycals and Glycal Derivatives
68
50% overall SPh 22
OPC
23
25
24
Scheme 5.
application of methods addressed to these ends, an expeditious synthesis of allosamidin was enabled. A general objective of the efforts in this area was an efficient route to glycals bearing C3 axial alcohol derivatives in the context of a range of substituents at C4. Glycals of this type had been difficult to synthesize [21] and rapid access to such derivatives would broaden the expanding collection of glycosyl donors and acceptors that could be incorporated into the assembly program. We found that Ferriertype rearrangement of tri-0-acetyl-D-gluca122 with thiophenol yielded 23 (Scheme 5) [22]. Oxidation of the a-(pheny1thio)pseudoglycal with DMDO and exposure of the resultant sulfoxide (24) to diethylamine triggered a [2,3]-sigmatropicrearrangement which resulted in the desired allal 25 in 96% yield. This sequence was expanded to include both allal and gulal derivatives as well as a range of substituents at C4. The issue of access to 2-aminohexose moieties has been impressively addressed by the azidonitration protocol of Lemiuex [23] and relies on the character of the C2 substituent to direct the outcome of any subsequent glycosylation. In this regard, azidonitration, while far from ideal in terms of stereoselection, remains one of the most useful methods to access the 2-amino-a-linkage. We, however, sought a new, direct method for introducing equivalent functionality through which stereoelectronic factors, rather than local steric factors, would determine the outcome of subsequent glycosylation. To this end, a key reaction, sulfonamidoglycosylation, was developed [22] (Scheme 6).
I(syn-Colli)zCi04
RRO o
> -HzNSO2P or h BrZNSOzPh
e
NH41
1
Scheme 6.
LTMP, AgOTf > -
RO
Ph02SNH 27 X = Br, I
26
28
R:q
29
30
3.4 KS-502 and Rebeccamycin
Bny% BnO
69
OSugar Ph02SNH 31
PhOzSNH
32 52%
34
64%
23%
Scheme 7.
This method, which involves trans diaxial addition of an N- halobenezesulfonamide to a glycal, leads to the 1-aminohexose 27. Alternatively, the action of IDCP (iodonium syn-collidine perchlorate) followed by benzenesulfonamide provides the same type of 2-halo-1-aminohexose. Treatment of 27 with base, likely proceeds through the 1,2-sulfonyloaziridine 28, which then reacts quickly and selectively with acceptors to form a P-linkage at the anomeric carbon. The scope of this general method was shown to include glycal- and nonglycal-containing carbohydrates as potential acceptors. Donors could include di- or higher saccharides terminating in a glycal linkage (Scheme 7). An additional benefit of this method was the finding that the intermediate halosulfonamides were often stable crystalline solids. The efficiency of coupling was later enhanced by the combination of stannylalkoxides in the presence of AgBF4 for the actual glycosylation reaction [24]. Furthermore, an iodosulfonamide can be readily converted to a corresponding ethyl thioglycoside, which in turn functions as a useful and alternative glycosyl donor. The adaptability of the sulfonamidoglycosylation to the iterative mode (glycals as donors and acceptors) made it particularly attractive for the synthesis of allosamidin (Scheme 8) [25]. The route to allosamidin utilized the sulfonamidoglycosylation for both glycosylation reactions, as well as the [2, 31 sigmatropic rearrangement methodology for both hexoses. Bromosulfonamidation of 36 (63%) followed by direct rollover with KHMDS in the presence of glycal 38 gave the P-linked disaccharide 39 in 81% yield. In turn, 39 then served as a donor in a second azaglycosylation with the aglycon derivative 41 to afford, after several steps, allosamidin (21). The efficiency of this synthesis served to reflect the power of iterative glycal assembly.
3.4 KS-502 and Rebeccamycin Glycosylated natural products, and other carbohydrate conjugates, present a challenging problem to synthetic chemists who must modify traditional carbohydrate
3 Iterative Assembly of Glycals and Glycal Derivatives
70
BnO
B n O KHMDS, 30%
-
-w
21 Allosarnidin
Scheme 8.
domain methodology to tolerate greater diversity present in the non-carbohydrate sector. In principle, incompatibility of synthetic methods to reach one domain can often limit options along a proposed route. KS-502 (43) and rebeccamycin (44) posed precisely this challenge and became the targets of our synthetic efforts in 1992-1 993. KS-502 (43) was isolated in 1989 [26] and identified as a specific inhibitor of calmodulin-dependent cyclic-nucleotide phosphodiesterase (CaM-PDE). The important roles of CaM and CaM-PDE in cultured cells and living systems underscored the utility of KS-502, perhaps as a valuable biological tool. Its structure comprises an interesting aryl furanoside for which new methodology was devised. Rebeccamycin (44)was shown to have antitumor activity against P388 leukemia, L1210 leukemia and B16 melanoma implanted in mice [27]. It is believed to impart this effect through the single strand cleavage of DNA. Water-soluble analogues Ho*
n-C7H 15
OH 42 KS 501 R = H 43 KS 502 R = C02H
Figure 4.
3.4 KS-502 and Rebeccamycin
71
have shown increased potency and are currently advancing through clinical trials [28]. The rebeccamycin structure consists of a symmetrical indolocarbazole chromophore P-N-linked to a 4-0-methylglucose residue. Synthetic efforts had concentrated on the aglycon portion of rebeccamycin, and an effective general methodology for the glycosylation step was sought to facilitate the total synthesis of this family of antitumor agents. While a unifying solution was pursued for these two glycoconjugate problems, total synthesis was not the sole inspiration for such efforts. Though sulfonamidoglycosylation provided routes from glycals to 2-aminoglycosides [ 14, 161, there was a more general need for a reliable and far-reaching route that would serve to convert glycals to common glycosides of glucose, galactose and mannose. The trichloroacetimidate donor methodology advanced by Schmidt [29], probably the single most powerful glycosylation method available, can often provide selective access to either a- or P-glycosides. We alternatively focussed on the application of glycal epoxides to tackle these and other problems. Such epoxides can participate in iterative strategies and can provide, in some circumstances, strikingly direct routes to polysaccharides. The existing record of a-epoxides as stereoselective glycosylating reagents was, at best, unimpressive when we launched our study. Access to such 1,2-anhydrosugar derivatives was awkward and their applications to glycosylations were beset by serious problems in stereoselectivity [30]. We first sought a direct and reliable route to 1,2-anhydrosugars. Furthermore, we hoped to gain advantages at the level of stereoselectivity by careful selection of resident functions. In particular, it was felt that resident groups bearing neighboring group participating functions, would tend to undercut clean formation of P-glycoside from a-epoxides. A major advance toward this goal came with the recognition that a variety of glycals react smoothly with 3,3-dimethyldioxirane (DMDO) [311. Glucal derivative 45 reacted with DMDO to give near quantitative yields of 46 and with >20: 1 aselectivity (Scheme 9). Galactal derivative 47 yielded the same result. In the allal series, glycal 49 underwent selective epoxidation instead from the P-face, while the gulal derivative 51 yielded a 1 : I mixture of epoxides. With these results in hand, the glycosyl donating abilities of these epoxides was explored (Scheme 10). Considerable experimentation indicated that ZnClz promoted selective p-glycosylation with alcohol acceptors, (e.g. 54, 55) whereas basic conditions promoted effective P-glycosylation only with moderately acidic acceptors (e.g. 56), such a s phenols. In some instances stannyl derived acceptors, conveniently generated in situ, afforded superior results. Subsequent to these investigations, it was found that oxirane 46 is actually among the poorest of donors [32], and that glycosylation yields could be improved by constraining the C3-C4 or C4-C6 oxygens into a cyclic motif. An interesting and useful variation on this procedure arises from the AgBF4 promoted reaction of an epoxide with a stannyl ether, which gives a-linked product. For example, treatment of 46 with 57 in the presence of AgBF4, followed by acetylation, cleanly affords 58 [33]. This method is presently limited to primary alcohol acceptors. These constraints underscore the need for a comprehensive solution to the challenging problem of stereospecifically generating a-glucosides.
3 Iterative Assembly of Glycals and Glycal Derivatives
72
0%
> -
>95%
45
0 % > -
TBSO
>95%
47
a:D
> 20:l
0% > -
>95%
TBSO
TBSO
49
Ph 0% > I
TBSO 51
>95%
50 > 2O:l P:a
?G
TBSO
52 1:l 8:a
Scheme 9.
R O *RO
OH
0-sugar
53
88%
42%
55
56
""d-""' /
Scheme 10.
67% (KzC03,18-C-6)
3.4 KS-502 and Rebeccamycin
73
Roao
1 .DMSO AqO
RO
pyridine F
RO 59
RO
61
60
Scheme 11.
The glycal epoxide method of glycosylation results in the placement of a free hydroxyl group at the 2-position of the hexose following coupling. This feature of the method enabled two alternative and useful advances (Scheme 11). First, the unique C2-hydroxyl group could be removed by the free-radical reduction of the derived pentafluorophenyl thionocarbonate (Barton deoxygenation). This sequence provides a synthesis for 2-deoxy-~-glycosides(60) [32, 341. Alternatively, the C-2 hydroxyl group could be inverted via an oxidation (AclO/DMSO)/reduction (NaBH4) protocol furnishing P-mannosides (61) [33, 351. Furthermore, the efficient and reliable route to a-glycal epoxides, facilitates numerous other methodologies leading to established donor functions (Scheme 12). Of particular importance is the fluoro-sugar type (cf. 66). Following benzylation of the uniquely free C2 hydroxyl group, derivatives such as 67 are produced. This method provides access to glycosyl donors ready for the powerful Mukaiyama promoter system [36]. We have often applied this protocol to allow for the stereoselective introduction of a-glycosides, as in 68.
62
63
BnNb
TBAF
<:
ZnCl2.71%
/
6
Bno BnO
NHB
OH 64
I
B\%c V
65
Scheme 12.
HX
X
Bno& BnO
AR'OH S & OR
66R=H 67 R = Bn
74
3 Iterative Assembly of Glycals and Glycal Derivatives " 5 ; H
nC5H11
184-6
H % H
q$(c!F?: En0
81% 69
"OH
15
,q
Rn6,H
OH
71
42 KS 501 R = H 43 KS 502 R = COfl
3 --L
48% 72
73
Rebeccamycin
Scheme 13.
The finding that the acceptor for a glycal epoxide can itself be a glycal established the basis for an iterative strategy for the synthesis of repeating p-glycosides. This concept has been a central component of our approach to oligosaccharide synthesis and has been adapted to solid support strategies as well [37]. The glycosidic bonds present in KS-502 and rebeccamycin provided especially attractive contexts for evaluation of the glycal epoxide method (Scheme 13). Treatment of the furanose glycal with DMDO gave the furanose epoxide 69 stereoselectively [38].Reaction of this epoxide with the phenol 70 afforded an 81% yield of the desired aryl-glycoside 71. Subsequent steps completed the synthesis of KS501 (42) and KS-502 (43). These furanoid epoxides were also used in the synthesis of nucleosides [39]. The extension of this procedure to the glycosylation of indoles was pursued in the context of rebeccamycin [40]. In this example, deprotonation of the differentiated indolocarbazole 72 followed by exposure of the resultant anion to glycal-epoxide 73 gave a 48% yield of the glycosylated product 74. Subsequent 2,2'-bis indole bond formation and deprotection yielded the glycoconjugate rebeccamycin (44).
3.5 Extension to Thioethyl Donors Galactal derived epoxy donors, such as 48, are particularly effective in enabling pgalactosylation. By contrast, glucal derived epoxides, lacking a comparable inter-
3.5 Extension to Thioethyl Donors
75
Lewis Acid
OH RO 75
77
RO 76
Scheme 14.
locking pattern between C3 and C4, are considerably more labile to typical Lewis acid promoters. This heightened instability brings with it significant limitations to the scope of their effectiveness as p-glycosyl donors. When the acceptor reactivity of the hydroxyl group in ROH is diminished, the yields of the glycosylation are compromised. In addition, the glycal epoxide method had not provided an efficient route to mannosides. For these reasons, we sought to extend the glycal epoxide method and turned to the use of thioethyl donors (75) for glycosylation and mannosylation (Scheme 14). Thioethyl and thioaryl glycosyl donors have previously been shown, in impressive studies by Garegg [41], to provide access to PI-4 glucosyl linkages in good yield. Donor activation is accomplished by either heavy metal salts or, directly and more efficiently, by other thiophilic reagents. The stereoselectivity of the glycosylation reaction is determined by the nature of the protecting group on C2. Indeed, it was found that glycals can be smoothly converted to thioethyl donors via glycal epoxides [42] (Scheme 15). The thioethyl glycosides thus produced, could be converted into the mannosides (75 + 85, Scheme 16). This overall inversion of configuration at C2 proceeded via an oxidation-reduction sequence to give, exclusively, the mannose derivative. The
EtSH cat. TFAA
B nO
71%
>95% 70
BnO& B nO
>95% w
BnOO 46
Scheme 15.
EtSH
-*cat. TFAA 78%
s OH . 81
EtSH cat. TFAA
03
BnO 6 BnO
U
-0TIPS
82
OH
80
79
E
45
BnO
-
U
84
76
3 Iterative Assembly of Glycals and GlycaI Derivatives 1. protect
R RO
asEt
O
OH
2. MeOTf DTBP 4A MS
75 1. ACZO DMSO pyridine 76 % 2. NaBH4
77
R
RO
O
MeOTf b -
F&SEt
85 R' = Ac, Bz, PIV
R O = L
S
* rR RO
DTBP 4A MS
a7
RORO -
Scheme 16.
resultant C2 hydroxyl groups can be protected with a variety of groups of known participatory capacity. The pivalate (Piv) derivatives were generally found to be the neighboring groups of choice for installing the desired linkage in that they provide very good margins of p-stereoselection without incurring problems of orthoester formation in competition with glycosylation (Scheme 17) [42].
3.5 Lewisy The antigenic blood group determinant LewisY (Ley) [43] is over-expressed in glycolipid and mucin glycoprotein form on many human tumor cells including those found in colon, lung, breast, and ovarian cancers. With this in mind, we set out to fashion vaccines based on the lipid and protein forms of Ley (Figure 5) [44]. To achieve these goals, we settled on the following target systems: (i) the natural product Ley-ceramide 94, (ii) a conjugate form for vaccination purposes 95, and a (iii) mucin mimic en route to a polypeptide-based vaccine (vide infra). The Ley tetrasaccharide determinant consists of a bis-fucosylated N-acetyl lactosamine. We reasoned that the iodosulfonamidation methodology could be used to install the amine function and would favor the subsequent incorporation of additional glycal units. It also seemed likely that both the Ley-ceramide target and the Ley-conjugate could be prepared from a common, but late, glycal epoxide intermediate. Concise construction of the Ley tetrasaccharide 98 commenced with lactal (96, Scheme 18) [44, 451. Protection of the primary alcohols, followed by engagement of the syn-vicinal diols as a cyclic carbonate, provided the lactal acceptor 97. Stereoselective introduction of the fucose moieties was achieved by applying a modifica-
77
3.5 LewisY MeOTf OTIPS B BnO n O
a
Brio*
DTBP
s E OPlV
t
OTIPS
OSugar
BnO
b *
OPlV
88
89
91
80%
BnO
MeOTf TIPSO n o % ,., BnO
4AMS DTBP ~
~
Bno
TIPSO BnO
93
92
0-Sugar
78%
91%
76%
Scheme 17.
tion of the original Mukaiyama conditions, using either 99 or 100. By starting with the glycal, the protecting group manipulations were minimal (2 steps). It remained however to convert the glycal function to the required lactosamine and to effect glycosylation to the pentasaccharide. In the event, 98 could be cleanly converted, by application of the iodosulfona-
OH
Figure 5.
94; R = Ceramide 95 R = Ally1
78
3 Iterative Assembly of Glycals and Glycal Derivatives
I
V
IDCP, 94% Oh
OBn
&
OB"
p
PhS02HN
102
75%
Scheme 18.
midation protocol, to 101 bearing the anomeric sulfonamide in excellent yield (94%). The latter underwent rearrangement to 102, using the 3-stannyl ether of 6Tips galactal, in 75% yield. This product contained the necessary lactosamine core linked in the desired p-configuration to the terminal galactal unit and constituted a protected Ley-pentasaccharide. After conversion of 102 to peracetate 103, the stage was set for divergent pathways to the ceramide (94) as well as to the ally1 glycoside (95). The later was the form we selected for conjugation to protein carriers, bovine serum albumin (BSA) and keyhole limpet hemocyanin (KLH). These were obtained from 103 upon treatment with DMDO followed by addition of the corresponding acceptors to the glycal epoxide. By application of iodosulfonamidation and the glycal epoxide methodologies, the targets were readily obtained. These syntheses paved the way for preclinical, and eventually clinical, investigations based on the Ley-pentasaccharide [46]. In these first generation vaccines, clinical evaluation of the immune response revealed that the antibodies displayed an apparent selective binding to Leyglycolipids, while relatively low antibody reactivity was noted with Ley-mucin pro-
3.5 Lewis”
79
teins. Implicitly, these immunological results posed the challenge of designing and synthesizing a closer mimic of a Ley-bearing m u c h glycoprotein. Before any effort to construct a mucin mimic could be launched, we were faced with the issue of glycoprotein-targeted vaccine design. We set out, therefore, to construct the simplest, and yet most realistic, molecules that would serve to direct the immune response against mucins. However, unlike Ley-ceramide, which is a discrete molecule, glyco-patterns in mucins may vary along the backbone and from one protein to the next. Hence, the uncertainties regarding glycoprotein structure render it quite difficult to design, with high confidence, molecules that will stimulate an immune response which targets mucin bearing cancer cells. The complexities of mucin structure notwithstanding, we proposed to synthesize several Ley glycopeptide-based vaccine candidates [45b, c]. To achieve this, we elected to incorporate the key common features of a mucin [43d, 471, including a primary structure characterized by sequentially arranged, and glycosylated, serine or threonine residues. The first carbohydrate of the glycodomain is a-0-linked GalNAc, and a number of intervening Gal and GlcNAc spacer units may insulate the core from the terminal region, which may bear, for instance, a blood group determinant like Ley. The glycopeptide domains of three of our mucin vaccines are shown in Figure 6 (104-106). Clustered pentasaccharide 104 satisfies the minimum requirements of the Ley tetrasaccharide attached to GalNAc-a-0-Ser. The GalNAc-P-0-Ser derivative 105, containing unnatural p-linkages, was also prepared. We wondered if such a ‘non-self’ structure might prove more immunogenic than 104 and still elicit antiLey antibodies. The hexasaccharide cluster, 106, has the natural GalNAc-a-0-Ser core as well as a spacer Gal between the Ley tetrasaccharide and the first carbohydrate and as such might be considered an even more realistic mimic of mucin structure.
B
R
Figure 6.
R
80
3 Iterative Assembly of Glycals and Glycal Derivatives
Having settled on a design, we returned to our original synthesis of Ley and identified the pentasaccharide 103 as a subgoal. If this pentasaccharide could be converted to the appropriate glycosyl amino acid bearing constructs, derivatives 104-106 should be accessible through standard solution phase peptide coupling. While iodosulfonamidation of glycals is often high yielding, and the adduct ready for subsequent glycosylation, removal of the 2-benzenesulfonamido group requires Birch (metal/ammonia) reduction conditions. This protocol was developed to accommodate the glycal moiety in the context of a complex oligosaccharide and achieves removal of benzyl groups without recourse to hydrogenation. However, dissolving metal reduction is not compatible with the base- and acid-sensitive glycoamino acid function. Thus, the iodosulfonamidation method could not be appropriated for the synthesis of Ley pentasaccharide bearing glycopeptides. To gain access to 104 and 105, pentasaccharide 103 would have to be transformed to a suitable donor substrate. The latter would be combined with the amino acid core for eventual peptide coupling (Scheme 19). In practice pentasaccharide 103 was subjected to Lemeiux azidonitration [48].This transformation was followed by reduction of the nitrate ester, and conversion of the resultant anomeric alcohol to the Schmidt trichloroacetimidate [49]. Donor 107, thus prepared, was ready for coupling with a serine acceptor. Compound 107 and FmocSerOBn (108), under promotion by TMSOTf, afforded the desired O-linked glycoamino acid, albeit in a ratio of 2.7: 1, a(109):b(ll0). After considerable experimentation, it was found that by altering the solvent composition, the relative ratio could be reversed to 1 : 1.7, a(109) :P(ll0). Thus both building blocks necessary for the construction of 104 and 105 were obtained from a common donor. Further transformations afforded the acids 111 and 112, respectively. These products were ready now for peptide coupling. In several instances, as illustrated above, glycosylation of elaborated 2-azido galactosyl donors seemed to be dependent upon the nature of the donor and the identity of the serine or threonine acceptor. In this context an acceptor such as 113 was preferred (Scheme 20). Assuming pentasaccharide 103 could be converted into a suitable donor, the glycoamino acid required for assembling hexasaccharide cluster 106 could be obtained by direct glycosylation with acceptor 113 [50]. To prepare 119, pentasaccharide glycal 103 was subjected to the action of DMDO, generating the glycal-epoxide donor. However, under normal promotion conditions acceptor 113 failed to couple with the donor epoxide. In order to enhance the reactivity of the donor, the epoxide was converted to the thioethyl donor 114, which, after protecting the newly generated 2-hydroxyl group as the benzoate (116), was coupled with 113 under MeOTf promotion. The glycosylation did proceed, but in low yield and was accompanied by N-methylation of the acetamide functionality, affording both the desired 118, as well as, the undesired methyl imidate. Thus, methyl triflate promotion of thioethyl donors, found to be fully compatible with glycal acceptors, becomes complicated in the presence of acetamides and this difficulty appears to be general. Though the imidate, formed as byproduct in the methyl triflate reaction, could be hydrolyzed back to the acetamide, other more direct methods were pursued. In this regard, it was found that in the presence of NIS/TfOH [51], the desired coupling was achieved in minutes and in excellent yield. Following further optimization, the preferred route to 118 is as follows. Pen-
3.5 LewisY
81
1. CAN, Nab, (66%) b
103
OCNHCCI,
2. PhSH, iP?!NEt (92%)
3. CbCCN. I(,CO,
(89%) 107
> 75%, 1:1 .7 109:110
75%#,2.7~1
WFmcc 108
0 109
AcHN
NiFmoc
OAc
,&&
OAc d 0 r A c
0 OAc
112
ACOoAc
Scheme 19.
tasaccharide glycal 103 was subjected to the action of DMDO and subsequently converted to the pentenyl donor 115 [52]. The 2-hydroxy glycoside was then protected as the benzoate. In the event, NIS/TfOH-promoted coupling of donor 117 with acceptor 113 cleanly afforded the desired serine-O-linked hexasaccharide 118. After manipulating the protecting groups, the glycoamino acid 119 was obtained. Sequential peptide coupling of 111, 112, and 119 provided the glycopeptide domains 104--106 and eventually several vaccine candidates. It was gratifying in this regard to find that preclinical immunological evaluation demonstrated that we had indeed constructed a vaccine which provokes an antibody response targeting
82
3 Iterative Assembly of Glycals and Glycal Derivatives
oac Ho
oms
-%J--.
1. DMDO
103
2. HSEI or 4-penlen-1-01
AcHN
'NHF~~:
113
116 w117
f
3
114: R ,
= SEI. & = H
115: R ,
= 0-4-Penteny1, R,= H
BzCl
(45% from 103)
116 RI = SEt. R2 = Bz
1
117 R1 = 0-4-Penteny1, R, = Bz
Scheme 20.
Ley-mucin bearing cells. Clinical evaluation of an anti-cancer vaccine based on 106 is currently well underway.
3.7 Globo H The hexasaccharide designated globo H (120, Figure 7) has been identified on human prostate, breast and small cell lung carcinomas, as well as in a restricted number of normal epithelial tissues [53]. Globo H was originally isolated in ceramide form from the human breast cancer cell-line MCF-7 1541. The enhanced expression of antigens assumed to be globo H on both primary and metastatic prostate cancer specimens drew us to the possibility of initiating a globo H-based vaccine strategy in prostate and other cancers 1551. At the planning stage of the synthesis 1561 it seemed reasonable that, similar to the Ley synthesis, late stage divergence from a hexasaccharide glycal epoxide could pro-
83
3.7 Globo H
H type 111 trisaccharide
Globotriose
120: R = Ceramide 121: R = Ally1
Figure 7.
vide both the ceramide form and the ally1 glycoside (121) for immuno-conjugation to KLH. As i1.s name indicates, globo H contains globotriose and an H type I11 module. The chemical union of two trisaccharides, a globo trisaccharide acceptor with an H type donor, would constitute a highly convergent approach this complex target. The galactosamine unit constituted added complexity, since iodosulfonamidation had not been attempted on a galactal unit. Additionally, a final 3 3 coupling using a galactal donor derived from an iodosulfonamide could serve to provide a dramatic demonstration of the method. The galactosyl units, including the galactosamine, might be derived from a common galactal building block. Similarly, the glucose unit of the lactosyl ceramide would come from glucal, while the terminal fucose could be installed at any convenient stage in the synthesis. Compound 122 serves as an excellent acceptor, due in part to its allylic nature, and does not suffer from competing glycosylation at the axial 4-position (see 123, Scheme 21) [56].In keeping with our earlier precedents, conversion of 122 to cyclic carbonate 124 followed by treatment of 124 with DMDO generates the expected glycal epoxide 125. This intermediate was coupled with 122 and 127 to give disaccharide building blocks 126 and 128 respectively. Disaccharide 125 was carried forward without protecting group manipulations and was fucosylated under Mukaiyama conditions (125 + 130, Scheme 22). This step required selective functionalization of the unreactive C2'-hydroxyl over the,
+
(123) (not observed)
Scheme 21.
126
128
84 0
3 Iterative Assembly of Glycals and Glycal Derivatives 0
OTPS
OH 0T1p
-
AgC104, SnCl2
\ k k & O e OH 125
130: R = H
48%
131: R = Protecting Group
BnO BnO
129
Scheme 22.
presumably less reactive, axial C6hydroxyl. In the event, under optimized conditions, the desired product was obtained in 48% yield. The undesired regioisomer was a minor byproduct. Still, this sequence provided the most direct route to the target trisaccharide glycal (a total of four steps from the common precursor, 6-Tips galactal). Protection of the lone hydroxyl was achieved in a straightforward manner (130 -+ 131). As will be shown, an even more serious unanticipated turn of events arose in attempting to use this glycal as a donor. The acceptor for the projected 3 + 3 coupling was prepared from fluoro-donor 134 and lactal 132 (Scheme 23). Compound 127 was readily converted to lactal acceptor 132, while 134 was prepared from selectively protected galactal 133. It seemed prudent to convert 133 to the more reactive 0-derivative 134 by direct opening of the epoxide with TBAF, followed by protection of the resultant hydroxyl. Mukaiyama coupling of 132 with 134 proved troublesome. While the yield was high (72%), the major impediment was selectivity ( a :p, 3: 1). The desired
I33
I27
OH OBn
o&
BnO-
Bno Bm 134
135
132
AgC104, SnCI2 132
+ I34 M 135
(88%, l O : l , a:p)
136: R = PMB 137: R = H
Scheme 23.
3.7 Globo H
85
product was obtained in only about 50% yield. Furthermore, as the reaction proceeded the reactive p-derivative 134 was slowly converted into the unreactive aderivative 135. Eventually, application, with slight modification, of the Suzuki [ 571 promotion procedure, using the superiluorophile CplZr(OTf)2, provided the desired product in 10: 1 ratio in an overall yield of >80% [ 5 8 ] . In fact, this promoter allowed for smooth conversion of either 134 or 135 to the desired product. This finding simplified the sequence considerably, in that treatment of 133 with DMDO could be followed by HF:pyridine effecting clean and rapid conversion to a-derivative 135. After removing the protecting group from 136, the acceptor trisaccharide (137) was ready for the key glycosylation reaction. As depicted in Scheme 24, compound 131 underwent smooth conversion to iodosulfonamide 138 in good yield. However, in practice, 138 failed to couple with trisaccharide 137. Undaunted we pursued the complementary route. Thus iodosulfonamide 138 was converted to the thioethyl donor 139. The 3 3 coupling of 139 and 137 was effected using methyl triflate in excellent yield, particularly considering the sophistication of the j’oined partners. A small quantity of an isomeric hexasaccharide was obtained. At the stage of hexasaccharide (140) it was difficult to rigorously assign the structure of the product, and it was primarily precedence upon which we base the structural assignment. Only after eventual conversion of oligosaccharide 140 to the deprotectetl ceramide, 141, did we realize that in the 3 + 3 coupling gave the undesired a-glycoside. This unpredicted turn of events is actually rather general [591. It was found that even monsaccharides consisting of 2-sulfonamide thioethyl galactosides resulted in glycosylation with poor selectivity. In the case at hand, modifying the protecting group on the C4-hydroxyl (see ‘R’ in 139) failed to reverse selectivity. Eventually, we would conduct the key glycosylation without any protecting group on the C4-position. However, C4 deprotection of 139 to give 143 (see Schemes 24 and 25) proved to be no simple matter, regardless of the identity of the protecting group. After considerable experimentation, it appeared as if the iodosulfonamidation and the ‘roll over’ reaction would have to be performed on the unprotected glycal 130.
+
131
IDCP L (82%. PhSqNH,) W
O
B
BnO OBn
13’,
Hexasaccharlde
139 b
60%
140
... Scheme 24.
UH
n 139
86
3 Iterative Assembly of Glycals and Glycal Derivatives 0 OTIpS 130
IDCP, PhSO N 2
50%
2
Oxo&-
p
LHMDS, HSEt L
PhS0,NH
79x
oy*o& p
om SEt !‘hSO,NH
143
I43
137, MeOTf L
70 - 85%
L
L
I20 and121
Scheme 25.
While this approach did eventually succeed, the path was not traversed without further obstacles (Scheme 25). Treatment of 130 with IDCP gave the desired iodosulfonamide. However, unlike similar derivatives, the immediate product was not stable to purification or storage and isomerized to an unproductive stereoisomeric donor. Usually, instead of attempting to purify the intermediate, 142 was taken on to the ‘roll over’ step providing the desired donor 143. Remarkably, methyl triflate promoted coupling of 143 with 137 gave the desired product in good yield. This compound was accompanied by a small amount of an undesired isomer. That the major product was indeed hexasaccharide 144 was demonstrated ultimately by its conversion to the natural product. In the end, 144 was converted to a peracetate glycal, which was converted to globo H-ceramide 120 and the ally1 glycoside 121. Compound 121 was taken on to vaccination trials in the form of a KLH conjugate and continues to be studied in various clinical settings with encouraging early results. While hard won, the lessons garnered in the globo H venture paid large dividends, in that a number of related carbohydrates were accessible using ‘unprotected 4-hydroxy’ donors similar to 143. Thus, asialoGM1 [59], GM1 [60], and the demanding fucosyl GM1 [61] have each been prepared for study. In retrospect, globo H was synthesized by implementing most of the glycal methods available, including glycal donors, acceptors, epoxides, and fluorides, as well as by extension of the iodosulfonamidation protocols.
3.8 KH-1 KH-1 (145, Figure 8) is one of the most formidable carbohydrate-based tumor antigens characterized to date [ 621. This nonasaccharide has been identified on the cell surfaces of all human adenocarcinoma cells thus far studied. Furthermore, its pres-
3.8 KH-1
P
AcHN
LeY
OH
AcHN
LeX
OH
87
OH
Lactose
145: R = Ceramide 146: R = Ally1
Figure 8.
ence has never been detected in normal colonic extracts. In keeping with our program goals we targeted both natural ceramide (145) and ally1 glycoside (146) forms for total synthesis [63]. Structurally. KH-1 can be viewed as a lactosyl ceramide bearing the Lewis' (Le') trisaccharide upon which is mounted the Ley tetrasaccharide [62]. In the synthetic planning stage, however, we set, as the cardinal strategic objective, maximum relief from blocking group manipulations. In an effort to implement a highly convergent route, we hoped to introduce all three fucosyl units in a single operation. The subgoal would then consist of assembling, in an iterative fashion, glycal disaccharides to form the hexasaccharide core. Importantly, the three oxygen centers to be fucosylated would be formulated such that a single deprotection maneuver would serve to unveil them concurrently. Pursuit of the target began with glycal building blocks 147-149, and from these three glycals, and fucosyl donor 150, the entire molecule would be constructed (Scheme 26). TES ether protection, for example resident in 151, was chosen as the mask for sites of eventual fucosylation. Thus, treatment of 147 with DMDO cleanly afforded the a-epoxide, to which the acceptors 148 and 149 could be added, in the usual way, in a parallel sequence giving glycals 151 and 152. Reiteration of glycal assembly was attempted after independently applying either the acetate (153) or an additional TES ether (154) to the newly generated hydroxyl of 151. Compound 152 was destined to house the lactose bearing the ceramide unit and was therefore converted to trio1 155. While 155 has several potential glycosylation sites, in principle, the C3' hydroxyl is the most reactive position. A suitable donor could be fashioned by subjecting 153, the core of the Le' sector, to IDCP iodosulfonamidation (see 156). Addition of ethanethiolate effected the roll over reaction and the donor was ready for coupling with 155. In the event, treatment of 157 with 155 under promotion of MeOTf did, in fact, give the desired tetrasaccharide 158, albeit often in low yield (35-55%). In addition, the reaction mixture appeared to contain significant quantities of at least one regioisomer.
88
3 Iterative Assembly of Glycals and Glycal Derivatives
\KO&
?go& m, TESO
OH En0
\,
151
KzC03
80%
I,,":
c
c
LHMDS. HSEt OYKo%
-*
TESO TESO PhS0,HN I60
PhS02HN 156
I59 R=SnBu,
oy&q Eso
Aco
SEl PhSO,HN
91%
1
I 159, AQEF,
V
I55 R = H
81%
/
157
155, MeOTf
35 - 55%
Scheme 26.
We wondered if the donor, one of our most activated, might be so reactive as to be insensitive to the subtle differences in the other hydroxyl units of the acceptor. To test this hypothesis, we attempted the union of 156 with the tin ether of the triol, 159. Direct 'roll over' proved to be quite slow, but very sensitive to the differences in hydroxyl reactivity in the acceptor. This chemistry constituted a very pleasing and attractive solution to the assembly of 158. The next plateau to be reached was seen to be that of the full hexasaccharide core (Scheme 26). In an effort to maintain the tempo of the synthesis, we proceeded on to another assembly iteration with minimal protecting group-based transformations. The use of a thioethyl donor was explored; however, in the end the direct roll over route proved more reproducible. To this end, iodosulfonamidation of 154 afforded 160. While presumably even more demanding than the earlier transformation, we opted to attempt the selective coupling of the tin ether of pentaol 161 with 160 (Scheme 27). This acceptor was readily available from the tetrasaccharide by simple removal of the cyclic carbonate (158 +.161). The reaction between 160 and 162 was performed, as before, in the form of the tin ether acceptor. Fortunately, the required
3.8 KH-1
89
161 R = H
162 R = SnBu,
163 R=H.R,=TES 164 R = A c . R ( = H
\\,
Scheme 27.
coupling could be executed in good yield (>60% of 163) and without detectable formation of side product arising from glycosylation at alternative acceptor sites. The culminating stage of the synthesis was confronted after protecting the four remaining hydroxyls and removing the silyl ether protection (163 + 164). The critical step, threefold fucosylation, was indeed accomplished through the reaction of 150 and 164. An exemplary yield (60%) of the nonasaccharide 165 was obtained. In the final steps, direct epoxide opening with ally1 alcohol proved optimal for preparing 146. Our alternative procedure was used to install the ceramide. Thus, thiolation of the epoxide generated from the reaction of 165 with DMDO. This was followed by protection of the resultant free hydroxyl to give donor 166 ready for coupling with a suitable acceptor. Following this sequence, the glycal was successfully taken on to the natural product (145). Conjugation of 146 to KLH provided a vaccine and pre-clinical immunological testing is under way. Application of iterative glycal methodologies requires glycal compatible promotion systems, and these promoters are now available. The ability to attenuate donor reactivity with the acceptor is frequently desirable, especially in the search for optimized routes, and was used to effect in the case at hand. By applying the full complement of glycal technology the target was obtained in a highly convergent and efficient way. In summary, the synthesis of KH-1 serves as a cogent demonstration
90
3 Iterative Assembly of Glycals and Glycal Derivatives
of glycal assembly and the minimized protecting group manipulations that this strategy can provide.
3.9 Concluding Remarks As shown above the logic of glycal assembly has been field tested in a variety of different contexts. While our focus here has been on the total syntheses themselves, clearly, much has been learned about the chemistry of glycals and their amenability to iterative coupling with suitable acceptors and donors. At this stage, with the required compounds in hand our attention is directed toward vaccine performance, with respect to eliciting active immunity against various cancers.
Acknowledgments
This work was supported by the National Institutes of Health (Grant Numbers: CA28824, A116943, HL25848). Postdoctoral Fellowship Support is gratefully acknowledged by L.J.W. (Grant Number: NIH: F32CA79120) and R.M.G. (NIH F32CA85894). We gratefully acknowledge Dr. George Sukenick of the SloanKettering Institute’s NMR Core Facility (Grant Number: CA-08748) for NMR and Mass Spectral Analyses. References 1. S. J. Danishefsky, M. T. Bilodeau, Angew. Chem. Int. Ed. 1996, 35, 1380-1419. 2. V. Q. G. De Lima, C. A. Albert, 0. G. De Lima, An. Acad. Bras. Cienc. 1964,36, 317. 3. J. J. Afora, C. F. Santana, 0. G. De Lima, Ann. CVIIth Int. Congr. of Hematology and Hemotherapy, Paris, 1978, p. 165. 4. (a) 0. G. Da Lima, F. D. Monache, I. L. D’Albuquerque, G. B. Marini-Bettolo, Tetrahedron Lett. 1969,471; (b) L. W. Bieber, A. A. Da Silva Filho, J. F. De Mello; W. Von Der Saal, 0. G. De Lima, Rev. Znst. Antibiot. (Recife) 1982-1983, 21, 27. 5. T. Oki, Anthracycline Antibiotics [Pap,. Symp. On Anthracylines, Aug 24-25,1981, New York] Khakeme, E. Ed.; Academic Press: New York, 1982; p. 75. 6. (a) R. U. Lemiew, S. Levine, Can. J. Chem. 1964,42, 1473; (b) R. U. Lemieux, A. R. Morgan, ibid 1965, 43, 2190. 7. (a) J. Thiem, H. Karl, J. Schwentner, Synthesis 1978, 696; (b) J. Thiem, H. Karl, Tetrahedron Lett. 1978, 4999; (c) J. Thiem, P. J. Ossowowski, Carbohydr. Chem. 1984, 3, 287; (d) J. Thiem, A. Prahst, I. Lundt, Justus Liebigs Ann. Chim. 1986, 1044; (e) J. Thiem, W. Klaffke, J. Org. Chem. 1989, 54, 2006; (f) J. Thiem, Trends in Synthetic Carbohydrate Chemistry, D. Horton, L. D. Hawkins, G. L. McGarvey (Eds.), ACS Symposium Series #396, American Chemical Society, Washington, D. C., 1989, Ch. 8. 8. (a) H. Paulsen, Angew. Chem. Int. Ed. Engl. 1982,21, 155; (b) D. R. Mootoo, P. Kondradsson, U. Udodong, B. Fraser-Reid, J. Am. Chem. SOC.1988,110, 5583. 9. (a) R. W. Friesen, S. J. Danishefsky, J. Am. Chem. SOC.1989,111, 6656; (b) R. W. Friesen, S. J. Danishefsky, Tetrahedron 1990, 46, 103. 10. K. Suzuki, R. Friesen, G. Sulikowski and S.J. Danishefsky, J. Am. Chem. SOC. 1990,112,8895.
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92
3 Iterative Assembly of Glycals and Glycal Derivatives
(d) B. W. T. Yin, C. L. Finstad, K. Kitamura, M. J. Federici, M. Welshinger, V. Kudryashov, W. J. Hoskins, S. Welt, K. 0. Lloyd, Int. J. Cancer 1996, 65, 406. 44. V. Behar, S. J. Danishfefsky, Angew. Chem. Int. Ed. Engl. 1994, 33, 1468. 45. (a) S. J. Danishefsky, V. Behar, J. T. Randolph, J. Am. Chem. SOC.1995, 117, 5701; (b) P. W. Glunz, S. Hintermann, J. B. Schwarz, S. D. Kuduk, X.-T. Chen, L. J. Williams, D. Sames, S. J. Danishefsky, V. Kudryashov, K. 0. Lloyd, J. Am. Chem. SOC.1999, 121, 10636; (c) Glunz, P. et al. Unpublished Results. 46. (a) V. Kudryashov, H. M. Kim, G. Ragupathi, S. J. Danishefsky, P. 0. Livingston, K. 0. Lloyd, Cancer Imunol. Immunother. 1998, 45, 281; Clinical data: (b) P. Sabbatini, V. Kudryashov, S. Danishefsky, P.O. Livingston, G. Ragupathi, W. Bornmann, M. Spassova, A. Zatorski, D. Spriggs, C. Aghajanian, S. Soignet, M. Peyton, C. O’Flaherty, J. Curtin, K.O. Lloyd, International Journal of Cancer, In Press. 47. (a) I. Brockhausen, in Glycoproteins, Montreuil, J., Schachter, H., Vliegenthart, J.F.G. Eds.; Elsevier: Netherlands 1995; pp. 201-259; (b) K. 0. Lloyd, J. Burchell, V. Kudryashov, B. W. T. Yin, J. T. Taylor-Papadmitrou, J. Biol. Chem. 1996,271, 33325; (c) S. Muller, S. Goletz, N. Packer, A. Gooley, A. M. Lawson, F. G. Hanisch, J. Biol. Chem. 1997, 272, 24780; (e) P. M. Rudd, R. A. Dwek, Crit. Rev. Biochem. Mol. Bio. 1997, 32, I ; (f) I. Carlstedt, J. R. Davies, Biochem. SOC.Trans. 1997,25, 214; (g) P. van den Steen, P. M. Rudd, R. A. Dwek, G. Opdenakker, Crit. Rev. Biochem. Mol. Bio. 1998, 33, 151. 48. R. Lemieux, R. M. Ratcliffe, Can. J. Chem. 1979, 57, 1244. 49. R. R. Schmidt, Angew. Chem. Int. Ed. 1986, 25, 212; R. R. Schmidt, W. Kinzy, Adv. Carbohydr. Chem. Biochem. 1994, 50, 84. 50. (a) X.-T. Chen, D. Sames, S. J. Danishefsky, J. Am. Chem. SOC.1999, 121, 10636; (b) J. B. Schwarz, S. D. Kuduk, X.-T. Chen, D. Sames, P. W. Glunz, S. J. Danishefsky, J. Am. Chem. SOC.1999,121, 2662. 51. (a) G. H. Veeneman, S. H. van Leeuwen, J. H. van Boom, Tetrahedron Lett. 1990, 31, 1331; (b) P. Konradsson, U. E. Udodong, B. Fraser-Reid, Tetrahedron Lett. 1990, 31, 4313. 52. D. Gordon, S. J. Danishefsky, Curb. Rex 1990,206, 361. 53. (a) P. 0. Livingston, Cancer Biol. 1995, 6, 357; (b) S. Zhang, C. Cordon-Cardo, H. S. Zhang, V. E. Reuter, S. Adluri, W. B. Hamilton, K. 0. Lloyd, P. 0. Livingston, Int. J. Cancer 1997, 73, 42; (c) S. Zhang, H. S. Zhang, V. E. Reuter, S. F. Slovin, H. I. Scher, P. Livingston, Clin. Cancer Res. 1998, 4 , 295. 54. (a) R. Kannagi, S. B. Levery, F. Ishijamik, S. Hakomori, L. H. Schevinsky, B. B. Knowles, D. Solter, J. Biol. Chem. 1983, 258, 8934; (b) E. G. Bremer, S. B. Levery, S. Sonnino, R. Ghidoni, S. Canevari, R. Kannagi, S. Hakomori, J. Biol. Chem. 1984,259, 14773. 55. (a) G. Ragupathi, S. F. Slovin, S. Adluri, D. Sames, I. J. Kim, H. M. Kim, M. Spassova, W. G. Bornmann, K. 0. Lloyd, H. I. Scher, P. 0. Livingston, S. J. Danishefsky, Angew. Chem. Int. Ed. 1999, 38, 563; (b) S. F. Slovin, G. Ragupathi, S. Adluri, G. Ungers, K. Terry, S. Kim, M. Spassova, W. G. Bornmann, M. Fazzari, L. Dantis, K. Olkiewicz, K. 0. Lloyd, P. 0. Livingston, s. J. Danishefsky, H. I. Scher, Proc. Natl. Acad. Sci. USA 1999,96, 5710; (c) Z.-G. Wang, L. J. Williams, X.-F. Zhang, A. Zatorski, V. Kudryashov, G. Ragupathi, M. Spassova, W. Bornmann, S. F. Slovin, H. I. Scher, P. 0. Livingston, K. 0. Lloyd, S. J. Danishefsky, Proc. Nat. Acad. Sci., 2000, 97, 2719. 56. T. K. Park, I. J. Kim, S. Hu, M. T. Bilodeau, J. T. Randolph, 0. Kwon, S. J. Danishefsky, J. Amer. Chem. SOC.1996, 118, 11488. 57. (a) K. Suzuki, H. Maeta, T. Suzuki Tetrahedron Lett. 1989, 30, 6879; (b) T. Matsumoto, H. Maeta, K. Suzuki, G. Tsuchihashi, G. Tetrahedron Lett. 1988, 29, 3567; (c) K. Suzuki, H. Maeta, T. Matsumoto, G. Tsuchihashi Tetrahedron Lett. 1988,29, 3571. 58. J. R. Allen, J. G. Allen, X.-F. Zhang, L. J. Williams, A. Zatorski, S. J. Danishefsky Eur. J. Chem. 2000, 1366. 59. 0. Kwon, S. J. Danishefsky, J. Am. Chem. SOC.1998,120, 1588. 60. S. K. Bhattacharya, S. J. Danishefsky, J. Org. Chem. 2000, 65, 144. 61. J. Allen, S. J. Danishefsky, J. Am. Chem. SOC.1999, 121, 10875. 62. E. Nudelman, S. B. Levery, T. Kaizu, S . 4 . Hakomori, J. Biol. Chem. 1986,261, 11247. 63. (a) P. P. Deshpande, S. J. Danishefsky, Nature 1997, 387, 164; (b) P. P. Deshpande, H. M. Kim, A. Zatorski, T.-K. Park, G. Rapgupathi, P. 0. Livingston, D. Live, S. J. Danishefsky, J. Am. Chem. SOC.1998,120, 1600.
Carbohydrates in Chemistry and Biology Beat Ernst, Gerald W. Hart, Pierre Sinay copyrightQ WILEY-VCH Verlag GmbH, 2000
4 Thioglycosides Stefan Oscarson
4.1 Introduction Thioglycosides are not very common in nature, only a few simple alkyl and aryl thioglycosides have been found as constituents of antibiotics from Streptomyces species [ 1-31. Although not really thioglycosides, glucosinolates with an anomeric sulfur are also well-known natural compounds [4, 51. In spite of their low natural abundance, thioglycosides and their chemistry have for a long time been a field of interest for many researchers, the first thioglycoside was synthesized in 1909 [6], and their basic chemistry was early reviewed [4, 71. But it is only recently that their excellent glycosyl donor qualities have been recognized. In the beginning of the seventies the first successful synthesis of a disaccharide was performed [S], but it was not until the middle of the eighties that enough efficient promoters were discovered to make glycosylation with thioglycoside donors into a general and accepted method. Since then and in a very short time-span, thioglycosides have become one of the most used type of donors, especially in glycosylations with oligosaccharide donors (block synthesis). There are already some reviews on the subject [9-121, and in the most recent complete list of published glycosylations during one year (1994) [ 131, thioglycosides were used as donors in about 20% of all reported glycosylations and in 35% of all couplings using oligosaccharide donors, competing well with the long established halide donors and the trichloroacetimidate method. The strength of thioglycosides as glycosyl donors is their easy synthesis (Section 4.2) combined with their stability, withstanding most reaction conditions used in e.g. protecting group manipulations and glycosylations, and at the same time their effective acth ation using chemoselective thiophilic promoters (Sections 4.3.2 and 4.4.1) and also easy transformation into other types of glycosyl donors (Section 4.3.1). Hence, they are perfectly fitted to be used in block synthesis of oligosaccharides, where stable oligosaccharide donors are a prerequisite. Their stability also makes them very apt in synthetic schemes where a number of chemical modifications are performed just prior to the glycosylations, as, e.g., in various types of
94
4 Thioglycosides
internal glycosylations (Section 4.4.2). In this article the synthesis of thioglycosides and their activation and application as glycosyl donors are discussed.
4.2 Synthesis of Thioglycosides Obviously one important feature of attractive glycosyl donors are their easy availability. The synthesis of the most used types of thioglycoside donors, mainly simple alkyl and aryl glycosides, is straight-forward and can be performed on a large scale using cheap chemicals. Often the product is crystalline and can be purified without chromatography. Numerous ways to prepare thioglycosides have been described [4, 10, 111, but for the easy production of thioglycosides mainly two synthetic methods are commonly employed, namely the reaction of a peracetylated glycose with a thiol in the presence of a Lewis acid and the reaction of an acylated glycosyl halide with a thiolate.
4.2.1 From Anomeric Acetates As depicted in Scheme 1 an anomeric acetate is usually easily substituted with a thiol under Lewis acid promotion to give thioglycosides. A standard procedure is to react a peracetylated aldose dissolved in CH2C12 with a slight excess of a thiol using a hard Lewis acid, e.g. BF3-etherate [ 141 or FeC13 [ 151, as promoter to give high yields of the 1,2-truns-product (neighbouring group participation). @-Acetateprecursors usually react faster [16], which is an advantage since this diminish the formation of 1,2-cis-impurities through Lewis acid catalysed anomerisation of the pthioglycoside [ 171. a/p-Mixtures are often obtained with less reactive mercaptans [18-201 or glycosyl acetates [21, 221. Variations of this method include the utilization of trialkylstannyl [23] or silyl derivatives [24] of the mercaptan. Advantages are less odor and sometimes higher yields owing to less formation of (1,Zcis- and dithioacetal) side products, disadvantages are the accessibility and cost of the reagents. Also, thioacetic acid can be used as nucleophile in this approach, to give anomeric thioacetates, which, in a two step-procedure, can be selectively S-deacylated and alkylated to give thioglycosides, a sequence often used in the synthesis of thiooligosaccharides [251.
A AcOc
O
Scheme 1.
GOAC OAc
BF3-Et20 EtSH CHC13 83%
AcO
SEt OAc
4.2 Synthesis of Thioglycosides ,OAc
95
,OAc
5 Et,O/H,O ACO*~~,, AcO AcO Br
84%
OAc
Scheme 2.
4.2.2 From Glycosyl Halides
This is a classical way to thioglycosides [6], in which an acylated glycosyl halide is reacted with a thiolate in a polar solvent to yield the 1,2-truns-thioglycoside (Scheme 2). Both alkyl-and aryl mercaptans have been used and good yields are usually obtained, although, especially with the more basic alkyl thiolates, a reacetylation step is often necessary prior to work-up and isolation of the product. If controlled conditions and an aprotic polar solvent are used, a S~2-typedisplacement reaction can be performed to give the inverted anomeric configuration in the product, e.g. a-glycosides from p-glycosyl halide precursors, in spite of the presence of participating 2-@protecting groups (Scheme 3) [26, 271. A modification is the use of phase-transfer conditions, allowing the use of free thiols and non-polar solvents in the reaction [28-301. Also with glycosyl halides as donors, alkylstannyl derivatives of the thiol have been employed as acceptors [23]. The lower reactivity of these reagents necessitates the use of elevated temperature or a promoter in these reactions, which often result in alp-product mixtures. Syntheses of thioglycosides are sometimes possible using Koenigs-Knorr glycosylation conditions (Scheme 4) [3l], although mercury(I1) salts have been rather frequently used to promote glycosylation with thioglycoside donors (Section 4.3.2). Indirect formation of thioglycosides can also be performed from glycosyl halides. Reaction with thiourea yields a pseudothiouronium salt, which (as the thioacetate above) can be hydrolyzed under mild, selective conditions to give the anomeric thiol, which then can be alkylated in an efficient, non-smelling procedure to produce
Scheme 3.
Scheme 4.
96
4 Thioglycosides
czA,& " 3 S
Aito+
acetone A c o ~ r 80%
AcO OAc
+
H20
Aco&sH AcO
YNH2 90% NH2
OAc
Scheme 5.
I IV
OH
Scheme 6.
thioglycosides (Scheme 5) [321, however hampered by the believed carcinogenity of thiourea (and alkyl halides).
4.2.3 Protecting Group Manipulations in Thioglycosides All common protecting groups such as esters (acetates, benzoates, pivaloates, leviulonates), ethers (benzyl, allyl, trityl, silyl), acetals (isopropylidene, benzylidene, cyclohexane-l,2-diacetal (CDA)) and orthoesters can effectively be introduced, manipulated and removed. Problems encountered are the removal of benzyl groups using catalytic hydrogenolysis (when Birch reduction conditions is an alternative), since the sulfur generally contaminates the catalyst, and sometimes participating of the anomeric sulfur to the 2-position and a consecutive 1 -+ 2-migration of the thio group. In an attempt to introduce a 2,3-orthoester into a rhamnose thioglycoside, using a trimethylorthoester in CH3CN the methyl 2-thio-2-deoxy glycoside was found to be the main product (Scheme 6) [33]. This migration could be avoided by changing the solvent to DMF or by removing the methanol formed in the reaction [34]. Similar 1,Zmigrations of thioglycosides have been utilized to give 2-thio-2-deoxy glycosides or glycosyl fluorides, which can be processed to 2-deoxy-glycosides (Scheme 7) [35, 361. Most functional group conversions abundantly used on carbohydrate derivatives are also compatible with thioglycosides, e.g. SN~-displacementsof sulfonates [37], azo transfer [ 381, and deoxygenation by tributyltin hydride reduction of thiocarbonyl carbamates [39]. During oxidations care has to be taken so not to obtain the sulfoxide derivative (if that is not desired). DMSO and also PDC-mediated oxidations can usually be performed without problems [40]. The thioglycosides are also stable towards various metal reagents such as Grignard and alkyl lithium reagents, which allows carbon elongation of carbohydrates and is a handy way to higher carbon sugar donors [41-431.
4.3 Glycosylutions with Thioglycoside Donors
97
1) i.BupSnO
MeOH
ii. BnBr, CsF
DMF, 66%
SEt
OH
SEt
2)CIC(S)OPh DMAP, CH$N
80% BnO BnO
OMe OBn
OMe OBn
Scheme 7.
4.3 Glycosylations with Thioglycoside Donors The stability of thioglycosides was early recognized, as was also their very mild conversion into glycosyl halides. Hence, thioglycosides were initially used as convenient precursors for various glycosyl halides, which then could be used as donors in glycosylation reactions. Later, it was found that thioglycosides could be activated directly by the use of chemoselective thiophilic promoters, and this discovery opened up a new field of applicable donors and glycosylation reactions. 4.3.1 A Two-step Procedure: Transformation of Thioglycosides into Other Types of Glycosyl Donors Glycosyl bromides and chlorides are effectively produced using bromine [44, 451 (also I-Br [46]) or chlorine [47] (also I-Cl [46]), nowadays often with CHzClz as solvent. Under these mild conditions even unstable glycosyl halides can be produced, as e.g. furanosyl [48, 491 and alkylated oligosaccharide bromides [50], and various acid-labile protecting groups are allowed as well. Glycosyl fluorides have been produced using numerous reagents [51], e.g. dimethyl(methy1thio)sulfonium tetrafluoroborate (DMTSB) [52], NBS-DAST [ 531, HF/pyridine [53]and Selectfluor [54]. Glycals can be obtained from phenyl thioglycosides by treatment with lithium naphtalenide under conditions compatible with acid4abile groups [ 551. Trichloroacetimidates may be obtained by the hydrolysis of the thioglycoside followed by the subsequent transformation into the imidate using trichloroacetonitrile and a base [56). Hydrolysis have been performed using various promoters (e.g. AgNO:3 [57], DMTSB [58],NOBF4 [59], and DMTST (dimethyl(methylthi0)sulfonium triflate) [43])in the presence of water. Sulfoxides are formed by oxidation using MCPBA or dimethyldioxirane [60].
98
4 Thioglycosides
/
J
-cl S
L
-0Ac o
7
W
N
O HN&I,
Scheme 8.
Anomeric esters have been synthesized through the action of silver [61] or mercuric [62]carboxylates, NOBF4/Ac20 [59] or NIS/RCOOH [63] on a thioglycoside. Since it is possible to activate a thioglycoside in the presence of a pentenyl glycoside [12], it should be possible to transform a thioglycoside into a pentenyl glycoside, but to my knowledge this sequence has not been explored. This convertibility is still an attractive feature of thioglycosides and the two-step glycosylation procedure is continuously being used in glycosylations and is a good complement to the direct one-step activation of thioglycosides. It is an important asset, since in oligosaccharide synthesis it is difficult to foresee which donor that will function best in which coupling, and, furthermore, since it allows thioglycosides as the sole source of donors, which simplifies the synthesis and diminishes the number of precursors that has to be made. Of the possible donors it is mainly the halides that have been employed. As mentioned, this was the original way to use thioglycosides in glycosylation reactions and already in the early publications on the conversion to halides, alkyl 0-glycosides was prepared by activation of the formed halide by a halide promoter, Ag2C03 [49] or Hg(CN)2 [64], in the presence of an alcohol (Scheme 9) both in situ and after purification of the halide. Both procedures have been used also with glycosyl acceptors. The in situ procedure [65-671 is advantageous if the isolation of the glycosyl halide is a problem. However, with the mild conditions used, this is normally not a problem and the halide is most often crudely purified before the glycosylation reaction, which, at least in our experience, generally gives a cleaner coupling reaction with less side-products. The in situ method, of course, also disqualifies thioglycoside acceptors in orthogonal couplings to build thioglycoside blocks (Section 4.4.1).
1) clp, CHpCIp
Ac N
SEt
benzene 69%
Scheme 9.
~
2) EtOH,Hg(CN)P
OEt
4.3 Glycosylutions with Thioglycoside Donors
99
BnO
SMe
BnO
OBn
OBn
AgOTf 63%
BnO
OBn
Scheme 10.
These transformations are possible to perform on complex oligosaccharides and a number of large, biologically important structures have been synthesized with this approach both using bromides 1501 (Scheme 10) and fluorides [68]. Treatment of perbenzylated thioglycosides with iodine in the presence of an acceptor gave good yields of 0-glycosides, but there is no discussion of glycosyl iodides as intermediates in the reactions [69]. No additional promoter was necessary, and acetylated thioglycosides were not affected.
4.3.2 Direct .4ctivation of Thioglycoside Donors Heavy Metal Salt Promotors The first efforts to use thioglycosides directly as donors were performed mainly with mercury(I1) salts as promoters. It was early recognized that mercury had a high affinity for the sulfur functionality [4], and effective hydrolysis of 1-thiofuranosides using mercuric chloride as catalyst instead of a mineral acid was reported [70]. An early attempt to methanolyze ethyl tetra-0-acetyl-1 -thio-P-D-mannopyranoside using HgC12 was nct successful [71], but when Ferrier et al. tried alcoholysis on unprotected phenyl 1-thio-D-glucopyranosides using Hg(0Ac)z or HgClz/HgO as promoters good yields of the corresponding alkyl glycosides with inverted anomeric configuration was obtained [8, 721. Using the perbenzylated phenyl 1-thio-p-Dglucopyranoside as donor and HgS04 as promoter the first disaccharide was produced (Scheme 11) 181. Other similar promoters were then tried, i.a. HgC12 1731, Hg(0Bz)z [74] and PhHgOTf [75],but especially with less reactive donors, e.g. peracylated, the yields were low and it was difficult to find a general high-yielding glycosylation method.
100
4 Thioglycosides
HgS04 THF, reflux, 3h 54%
Scheme 11.
However, if a heterocyclic aryl thioglycoside was used as donor a more efficient activation with metal salts was accomplished. HgClz-promoted methanolysis of phenyl thioglycosides had been found to be faster than for the corresponding ethyl thioglycoside (compare Section 4.4.1), and with the heteroatom in the aryl system an even faster metal-ion promoted reaction took place, indicating that the heteroatom facilitated the activation of the thioglycoside (remote activation concept [76]). Mainly 2-pyridyl thioglycosides have been employed (Scheme 12), but also e.g. 2-pyrimidinyl [771 and benzothiazole thioglycosides have been used, and also different metal salt promoters, e.g. Hg(N03)Z [78], CuOTf2 [79], Pb(C104)2 [80, 811, or AgOTf [80, 82, 831. More recently, Mereyela et al. in a number of papers introduced methyl iodide as a promoter for 2-pyridyl thioglycosides [ 84-87]. Halonium, sulfonium and carbonium type promoters Owing to the many advantages of thioglycoside donors and the promising but so far limited success with heavy metal salt promoters a quest for more generally effective promoters was launched. Starting with NBS in 1983 [88] and especially with methyl triflate (MeOTf) in 1984/5 [89-911 and DMTST in 1986 [92] a seemingly never ending spectrum of new promoters has been reported (Table l), most examples variation of a common theme, soft electrophile reagents (halonium or sulfonium) with non-nucleophilic counter ions (triflate or perchlorate), but also electrochemical and radical activation have been described (Section 4.3.2). In spite of the array of different promoters and thioglycoside donors developed and reported, only a few have so far been proven generally useful in more extensive oligosaccharide synthesis. Among donors the methyl, ethyl and phenyl thioglycosides are by far the most utilized, and MeOTf, IDCP(T), DMTST and NIS alone or
OBn Ac0-q
Me0
scheme 12.
N
+ HO& Me0
Pb(C'04)2 THF,8h 59%, C@J 3:l
MeO
4.3 Glycosylations with Thioglycoside Donors
101
Table 1. Thiophilic promotors. Promoter
References
MeOTf DMTST/DMTSB NBS N BS/TfOH NBS/BQNOTf NBS/LiC104 NIS, NIS/TfOH or TMSOTf NIS/AgOTf or I3t3SiOTf IDCP IDCT Methylsulfenium triflate/bromide (MeSOTf/Br) 12
IBr Iz/AgOTf PhSOTf PhSeOTf NOBF4 N-PhSePhthOTf S02C12/TfOH PhIO-Tf20
in combination with triflic acid or silver triflate cover more or less completely the spectrum of more frequently used promoters. Numerous highly complex structures have been synthesized using these combinations verifying the impressive utility of the method. A few examples, exhibiting the synthesis of structures from N-linked glycans [91], the Salmonella LPS-core [ 1lo], and gangliosides [ 1111, are shown in Schemes 13-15. The methodology are compatible with almost all types of donors, and thioglycoside donors of e.g. furanoses, heptoses, Kdo, neuraminic acid, deoxy sugars, and uronic acids have been prepared and used successfully in glycosylation reactions. These promoters also complement each other nicely regarding reactivity, from the least reactive IDCP and MeOTf through the intermediate DMTST up to the most reactive NIS/TfOH. This promoter reactivity difference in combination with the different reactivity of donors and acceptors allows many practical orthogonal couplings between thioglycosides (Section 4.4.1). Notwithstanding the efficiency of these promoters and thioglycosides as donors, problems can, of course, be encountered in various applications. The problems are connected both to the type of thioglycoside used as well as to the promoter employed. Regarding the promoter, MeOTf can, if the acceptor is unreactive, give methylation instead of glycosylation of the acceptor hydroxyl group [ 1121, although this alkylation is normally surprisingly slow in the absence of base. The use of DMTST together with N-acetamido sugars might lead to thiomethylation of the amide group [113]. NIS, due to the
102
4 Thioglycosides
MeOTf
1
W OH L n OBn
Scheme 13.
nucleophilicity of the counter ion (as compared to triflate in most other promoters), can, once more in the case of unreactive acceptors, give rise to N-succinimide glycosides of the donor as the major product (Scheme 16) [39, 114-1 161. The obvious considerations that soft nucleophilic centres, like e.g. double bonds, should not be allowed in the donor/acceptor, since these would compete with the sulfur in its reaction with the electrophilic promoter, is not as adamant as perhaps expected. Accordingly, glycosidation with thioglycoside donors and allyl and pentenyl groups both in the donor and the acceptor have been performed using controlled conditions (Scheme 17) [ 117-1 191. Problems have been encountered when the acceptor hydroxyl group is adjacent to an allyl protecting group, which have resulted in internal addition to an activated double bond being the major reaction (Scheme 18) [97, 1131. Common problems in oligosaccharide synthesis not directly related to the method of direct activation of thioglycoside donors, such as for example transacylations or formation of orthoesters, when using 2-0-participating groups, or glycal or 1,6-anhydro derivative formation of the donor can, of course, also be encountered [90, 1lo]. As is the case with most glycosylation reactions, i.a. because of their complexity, no truly thorough mechanistic investigation has been performed on the direct activation of thioglycosides. An obvious general mechanism (Scheme I9), very similar to the one suggested for other types of glycosylation reactions, in which the soft
4.3 Glycosylutions with Thioglycoside Donors
OSP
BnO
BnO
BnO
OAc SM.3
BzO BzO
AcO
EtNBr, 90%
HO
OAc
OH
0
Scheme 14.
103
104
4 Thioglycosides
BzO
BzO?'$ko&sph BzO
:
r
s
E
e
OBn OBn
OB+oBn
'f
1) NlSRfOH 86%
NPhth
OBn
2) NaOMe
OBn
OBn
OBn
SMe
OAc
') DMTST 2) Ac20, pyridine, DMAP 3) CAN 55%
OBz
AcO
OBn
NlSKfOH 60%
OBn
OBn
OBn OBn
Scheme 15.
SE = CH2CH2SiMe3
OBn
4.3 Glycosylutions with Thioglycoside Donors
105
BnO
BnO O(CH2)&02Me NHAc
HO
Scheme 16.
DMTST
EQO OSE
92% dp 2.3/1 or NIS/AgOTf (75%)
N3
OBn
Scheme 17.
DMTST
OBn
SEt
SEt
Scheme 18.
X-
A
+HX
Scheme 19.
electrophile E+ (e.g. I+ (NIS, NBS, IDCT(P), Mef (MeOTf) or MeS+ (DMTST(B), MeSOTf(Br)) attaches to the sulfur functionality, whereafter the anomeric carbonsulfur bond is broken to generate an oxycarbenium ion (with some counterion X-, e.g. TfO- or C104), which then is attacked by the acceptor nucleophile, sometimes preceded by the formation of a cyclic acyloxonium ion if 2-0-participating groups are used, to give the 0-glycoside, is more or less commonly accepted, but the intrinsic details, like the exact nature of the intermediates or rate-determining step, are not known, and are also probably very different for different combinations of acceptor/donor/promoter and reaction conditions. No kinetic studies have been performed. Some studies of the anomerisation of alkyl p-D-thioglycosides with IDCP have been carried out showing this to be an intermolecular process and bulky
106
4 Thioglycosides
SEt
DMTST Et20 76% a
OMe
OMe
OBz
63% p
Scheme 20.
alkyl groups to be inert (however possible to use as donors) [17, 1201, and Crich and Sun have identified a stable anomeric triflate as intermediate when activating thioglycosides with PhSOTf at -78 “C [loll, but mostly mechanistic suggestion are based on product structure and distribution in combination with the understanding about mechanisms in similar reactions. Since the major outlines of the mechanism is the same, with common intermediates, as for most other types of glycosylations, much of the knowledge about the stereochemical outcome of glycosylation reactions with other type of donors is valid also for thioglycoside donors. Consequently, the use of 2-0-participating groups will lead to 1,2-trans-glycosides, if there is not a mismatch between donor and acceptor [ 1211. Furthermore, with non-participating groups, the use of diethyl ether as solvent will improve the alp-ratio [ 1221, whereas the use of acetonitrile will give predominantly P-glycosides, especially with primary acceptors [ 1231. Boons et al. advocate the use of toluene/dioxane as an even better a-directing solvent mixture [124].The stereochemical outcome is also dependent on the promoter used and on the protecting group pattern (even apart from the 2-0-protecting group). To generalize, IDCP and DMTST are good a-directing promoters whereas MeOTf and NIS are not (Scheme 20 [ 1251) [ 124, 1261. Bulky groups at 0-6 of glucopyranoside donors [ 1271 and electron-donating ester groups at 0-4 of galactopyranosides [ 1281 have been shown to increase the a//p-ratio in the disaccharide products due to steric and participating effects, respectively. As so often in glycosylation reactions these findings are only guidelines, and an optimisation is normally necessary for each specific reaction. Single-Electron Activation
Thioglycosides can also be activated by a single-electron transfer mechanism (Scheme 21). In these reactions a radical cation is generated by the transfer of a single electron from the sulfur to a suitable electron acceptor. Subsequent heterolytic cleavage of the anomeric linkage yields a sulfur radical, which dimerize to a disulfide, and an oxocarbenium ion, which, as in “normal” glycosylations, can undergo a nucleophilic attack by an alcohol to generate an 0-glycoside. The single electron transfer can be accomplished either photochemically [ 1291, electrochemically [130, 1311, or chemically [132]. Aryl thioglycosides in CH3CN/MeOH (9: 1) were irradiated in the presence of
107
4.3 Glycosylutions with Thioglycoside Donors single-
+I12 RSSR Scheme 21.
1,4-dicyanonaphtalene to give methyl glycosides [ 1291. However, the choice of protecting groups was a problem. Benzyl protected thioglycosides gave mainly other products, whereas acetylated derivatives were not activated. Hence, only permethylated compounds were compatible with the reaction conditions to give the desired glycosides. Electrochemical glycosylation was possible using both phenyl (also p-methoxyphenyl [131]) and ethyl thioglycosides [130, 1331. Acetylated donors were found to be less efficient whereas both benzylated and benzoylated donors gave good yields of disaccharides (Scheme 22). Acylated donors gave, as expected, exclusively the 1,2-truns-products, and also the benzylated donors gave predominantly the pproducts, probably due to the use of CH3CN as solvent in the reactions. Chemically, single electron transfer glycosylations have been effected by the use of the commercially available electron transfer reagent tris(4-bromo-pheny1)ammoniyl hexachloroantimonate (BAHA) as promoter. Once more, both ethyland phenyl thioglycosides, benzylated and benzoylated, could be utilized as donors to afford disaccharides in high yields (Scheme 23) [ 1321. The efficient synthesis of a trisaccharide have been reported [134],but, in spite of the promising results no other oligosaccharide syntheses have been published using this methodology. Glycosylations performed with an electron transfer quencher (1,2,4,5-tetramethoxybenzene) present showed that the reactions are completely quenched in CH2C12 but only partly in CH3CN (28% yield), giving evidence for the single-electron transfer mechanism, but also suggesting alternative mechanistic possibilities in CH3CN [135].
BBnOn
O
a SPh + OBn
Brio%
HO
anodic oxidation BBnO n -e__.___) CH3CN
BnO OMe 73%, a/p 1.3
OBz Bzo*SPh BzO
OBz
+
anodic oxidation -eCH&N
&fo&$,
~
BnoOMe
Scheme 22.
45%
O BnO
G
o
6
BnO BnoOMe
B5:oGo&$, BzO
Brio
BnoOMe
108
4 Thioglycosides
Q BnO& BnO
SPh +
OBn
::o
4
*+
SbCIi
a
Br B r * BBnO n BnO CH3CN OMe 86%, a l p 1 :2
OBz BzO Bzo$&SEt
OBz
O BnO
G 0 BnO
G BnoOMe
OBz
+
:to+
CH&N BAHA BnoOMe
81%
Bi!o&oG BzO
Brio BnoOMe
Scheme 23.
Other Types of Donors With an Anomeric Sulfur
Although not proper thioglycosides, various other derivatives with an anomeric sulfur have been synthesized and used as glycosyl donors. Kotchetkov et al. introduced, as a complement to their cyanoorthoester 1,2-truns glycosylation method, (3-glucopyranosyl thiocyanates as 1,2-cis-glycosyl donors with tritylated acceptors and trityl perchlorate as promoter [136]. With a nonparticipating group at 0-2 the glycosylation is completely stereoselective to give the inverted anomeric configuration in the product (Scheme 24). Also polycondensation using this approach has been reported [137]. Anomeric carbodithioates, both 0-and N-linked have been investigated. The 0ethyl derivative, i.e. the ethyl S-glycosyl xhantate, of 2-azido-galactopyranoseswas found to be an efficient donor activated by either Cu(0Tf)z or DMTST [138, 1391, but especially the same type of derivative of N-acetyl-neuraminic acid has proven to be an excellent alternative as a sialic acid donor, which has found general applications activated by thiophilic promoters as DMTST or MeSOTf (Scheme 25) [ 1401421. The analogous anomeric N-piperidine derivatives could be activated not only by thiophilic promoters (MeOTf and DMTST) but also by AgOTf and various Lewis acids, e.g. SnC14 and FeC13, to allow orthogonal couplings with thioglycosides and the building of thioglycoside donor blocks (Scheme 26) [ 1431.
AcoG,,, + Tf)o&oAc
AcO
OBn
= +
OAc
CHzC12 77%
OAc AcO
Scheme 24.
4.4 Applications of Thioglycosides OAc OAc COOMe - - ...-
-
Acol*%
OEt
'dS\
AcHN AcO
MST CH3CN CH&
~
109
AcHN AcO
Scheme 25.
AAcOc
O
a
s
OAc
K
Ng CH& 79%
'OBn
Scheme 26.
Also anomeric phosphorothioates have been explored. Perbenzylated S-glycosyl phosphorodiamidimidothioates promoted by 2,6-lutidinium p-toluenesulfonate gave good yields of disaccharides and 1,2-cis-selectivity(Scheme 27) [ 1441. If BQNI was used as an additive in the glycosylation even higher 1,2-cis-selectivitywas obtained. S-glycosyl phosphorodithioates as glycosyl donors are discussed in a number of articles, both 2-deoxy derivatives activated by AgF [ 1451 or iodonium promoters [ 1461 to give alp-mixtures of disaccharides, and 2-0-pivaloyl derivatives activated by MeOTf to give 1,2-trans products (Scheme 27) [147]. Although stable under some reaction conditions, none of the donors above exhibit the superior stability of thioglycosides and are therefore not an alternative to
BnO toIuene 85%
'OBn
BnO
BnO& BnO bpiv
Scheme 27.
-
MeOTf
CH2CIz 55%
-
PivO
110
4 Thioglycosides
thioglycosides, e.g. in block synthesis, but rather an addition to the spectrum of less stable glycosyl donors, which might find use in applicable cases.
4.4 Applications of Thioglycosides The stability of thioglycosides in combination with their easy activation makes them highly suitable as donors in most glycosylation strategies and technologies, e.g. in block synthesis as well as in techniques where the donor is manipulated before glycosylation and in solid phase synthesis. 4.4.1 Block Syntheses, Orthogonal Glycosylations The concept of orthogonal glycosidations will be discussed in more detail in other chapters in this book, but since the possibility of oligosaccharide block syntheses is one of the major advantages of thioglycosides, a few aspects of orthogonal glycosidations involving thioglycosides will complementarily be discussed also here. Thioglycosides as Acceptors
Most other donors can effectively be used in couplings to thioglycoside acceptors to give thiooligosaccharide blocks, e.g. halide donors using halide-assisted conditions or heavy-metal salt promoters, trichloroacetimidate donors with hard Lewis acid promoters, selenoglycosides with AgOTf activation and sulfoxide donors with TMSOTf or triflic anhydride as promoter. The efficiency in the couplings are dependent on the reactivity of the acceptor and donor and complications can arise especially with activated thioglycoside acceptors, when transglycosylation of the thiol is an often observed side reaction (Scheme 28) [89, 148, 1491. Taking the knowledge of the protecting group influence on the reactivity into account, it is normally possible to design an efficient way to thiooligosaccharide blocks, however, the protection group manipulations might be tedious and surprises might be encountered (Scheme 29) [ 1171.
Hg(CN)z or HgBr2 or . . O M B r OAc
Scheme 28.
+
A c O W S E t toluene
OAc 6O-8OYo
4.4 Applications of Thioglycosides
I
tES,&&ThTBDMSO P
11 1
bBZ
c AgOTf --
BnO
SEt
Br
OBz
Scheme 29.
Thioglycosides as Both Donors and Acceptors
The protecting group pattern is known to have a large influence on the reactivity of the donor (and of the acceptor). This has been recognized for a long time, but only been possible to utilize effectively in synthetic schemes with the event of stable donors, which has allowed the formation of donors with almost any type of protecting groups and pattern. This reactivity difference can be utilized to permit orthogonal glycosylations between thioglycoside donors (reactive, alkyl protecting groups) and acceptors (inreactive, acyl protecting groups) exploiting less reactive promoters, which only react with activated thioglycosides (Scheme 30) [97]. The idea of using the reactivity difference more systematically was developed by Fraser-Reid et al. in orthogonal couplings between armed and disarmed pentenyl glycosides [ 1501. This concept has been further developed by quantitative determination of the reactivity of donors by the use of competitive glycosylations [ 1511. Recently, fifty thioglycosides with different protecting group patterns have been synthesized and their reactivity has been determined. Through this approach it has been possible lo assign a reactivity constant to each thioglycoside, which allows the planning of synthetic schemes involving orthogonal glycosylations between thioglycosides and one-pot synthesis of oligosaccharides and also a possible computation of the selection process [ 1521. However, with thioglycosides there is an additional possibility to change the reactivity, namely through changing the alkyl (aryl) group of the anomeric thiol. This anomeric activation/deactivation prospect might be compared to the reactivity dif-
B"O& BnO
SEt
OBn
Scheme 30.
&-
+BB'po
IDCP
OBz
SEt (CICH2)2/Et20 84%
BnO SEt OBz
1 12
4 Thioglycosides OBn
SEt + H O
BnO OBn
OBn
72%
Scheme 31.
ference between halide sugars (iodo > bromo > chloro > fluoro) and the inactivation of pentenyl glycosides by bromination of the double bond, but the spectra allowed with thioglycosides are broader. Both steric effects and electronic effects can be utilized to influence the reactivity. Hence, thioglycosides of sterically crowded mercaptans, as e.g. 1,l-dicyclohexylidenemethyl mercaptan, show lower affinity for thiophilic promoters and can be used as acceptors in condensations with ethyl thioglycosides as acceptors [ 201. The higher stability of phenyl thioglycosides as compared to ethyl thioglycosides with IDCP as promoter has been shown [ 1191, and this reactivity difference have been further proved by glycosylations with p-tolyl thioglycoside donors and thioethyl acceptors using NIS/TfOH as promoter (Scheme 31) [153]. By introducing various substituents into the aromatic ring of phenyl thioglycosides a variety of reactivity can be obtained. On the extreme of the unreactivity side is the p-nitrophenyl thioglycoside, where activation does not have to be feared even with efficient promoters. On the contrary, sometimes deactivation of the acceptor hydroxyl group might be a problem and for continued use as donor the p-nitrophenyl group has to be activated as the acetamido analogue. This sequence has been investigated [ 154, 1551, but problems often arise and the scope of the methods appears to be limited, however effective with sialyl derivatives [ 1561. p-Halogenphenyl thioglycosides might be interesting compounds of intermediate reactivity. With methyl triflate or DMTST as promoters, acylated derivatives are not activated, whereas the use of NIS/triflic acid smoothly allows the use of these derivatives as glycosyl donors [ 1571. 4.4.2 Intramolecular Glycosidations To obtain desired regio- and stereoselectivity in glycosidations, new glycosylation methodology are continuously developed. Recently two intramolecular variants, internal acceptor delivery and intramolecular glycosidations of spacer prearranged glycosides, were described. In both of these approaches a number of reactions are performed on the acceptor/donor pair before the glycosidation reaction, and therefore thioglycosides as donors have been an obvious choice. In the internal delivery approach the acceptor hydroxyl group is linked to the 2-OH of a thioglycoside donor via a labile acetal linkage. Activation of the thioglycoside also breaks the acetal bond and the acceptor is transferred stereospecifically to the anomeric site of the activated donor to give high yields of
References
1 13
1,Zcis-glycosides, also the otherwise difficult obtainable P-mannopyranosides and P-fructofuranosides [ 158-1621. In the intramolecular glycosidation using prearranged glycosides the donor and acceptor are linked through a spacer via other hydroxyl groups than the ones that will be part of the new glycosidic linkage. By using various attachment sites and various spacers, regio- and stereoselective glycosylations can be performed [ 1631651. 4.4.3 Solid Phase Synthesis Since thioglycosides are possible to synthesize with almost any type of protecting group pattern and since they are shelf-stable, they should be very suitable as donors in a commercial approach to solid-phase synthesis of oligosaccharides. That they are excellent donors also in a solid-phase approach is shown, i.e., by the publications from Nicolaou et al. in which up to dodecasaccharides are synthesized on polystyrene beads using thiophenyl and thiomethyl glycoside donors and DMTST as promoter [1166, 1671. References 1. R. R. Herr, J , Am. Chem. Soc., 1967,89,2444-2447. 2. H. Hoeksema, B. Bannister, R. D. Birkenmeyer, F. Kagan, B. J. Magerlein, F. A. MacKellar, W. Schroecler, G. Slomp, R. R. Herr, J. Am. Chem. Soc., 1964,86, 4223-4224. 3. H. Hoeksema, J. Am. Chem. Soc., 1964,86, 4224-4225. 4. D. Horton, D. H. Hutson, Adv. Carbohydr. Chem., 1963, 18, 123-199. 5. V. Gil, A. J. MacLeod, Phytochern., 1980,19, 2071. 6. E. Fischer, K. Delbriick, Ber., 1909, 42, 1476-1482. 7. A. L. Raymond, Adv. Carbohydr. Chem., 1945, 1, 129-145. 8. R. J. Ferrier, R. W. Hay, N. Vethaviyasar, Carhohydr. Res., 1973, 27, 55-61. 9. P. Fugedi, P. J. Garegg, H. Lonn, T. Norberg, Glycoconj. J., 1987, 4, 97-108. 10. T. Norberg, in S. H. Khan, R. A. O’Neill (Eds.): Modern methods in Carbohydrate Synthesis, Harwood Academic Publishers 1995, p. 82-106. 11. P. J. Gareg,g, Adti. Carbohydr. Chem. Biochem., 1997, 52, 179-205. 12. G. H. Veeneman, in G.-J. Boons (Ed.): Carbohydrate Chemistry, Blackie Academic & Professional 1998, p. 98-174. 13. F. Barresi, 0. Hindsgaul, J. Carbohydr. Chem., 1995, 14, 1043-1087. 14. R. J. Ferrier, R. H. Furneaux, Carbohydr. Res., 1976, 52, 63-68. 15. F. Dasgupta, P. J. Garegg, Acta Chem. Scand., 1989,43,471-475. 16. R. U. Lemieux, Can. J. Chem., 1951,29, 1079-1091. 17. B. Lindberg, B. Erbing, Acta Chem. Scand., 1976, B30, 611-612. 18. W. V. Dahlhoff, Liebigs Ann. Chem., 1990, 1025-1027. 19. S. A. Galema, J. B. F. N. Engberts, H. A. v. Doren, Carbohydr. Res., 1997, 303, 423-434. 20. G. J. Boons, R. Guertsen, D. Holmes, Tetrahedron Lett., 1995, 31, 6325-6328. 21. P. J. Garegg, L. Olsson, S. Oscarson, J. Org. Chem., 1995, 60, 2200-2204. 22. T. Nakano, Y. Ito, T. Ogawa, Tetrahedron Lett., 1990, 31, 1597-1600. 23. T. Ogawa, M. Matsui, Carbohydr. Res., 1977, 54, C17-C21. 24. V. Pozsgay, H. Jennings, Tetrahedron Lett., 1987,28, 1375-1376. 25. H. Driguez, Topics Curr. Chem., 1997, 187, 85-1 16. 26. M. Appani, M. Blanc-Muesser, J. Defaye, H. Driguez, Can. J. Chem., 1981, 59, 314-320.
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1 16
4 Thioglycosides
124. A. Demchenko, T. Stauch, G.-J. Boons, Synlett, 1997, 818-820. 125. P. Svahnberg, Licenciate Thesis, Stockholm University 1999. 126. P. J. Garegg, S. Oscarson, H. Ritztn, M. Szonyi, Carbohydr. Rex, 1992, 228, 121-128. 127. S. Houdier, P. J. A. Vottero, Carbohydr. Res., 1992,232, 349-352. 128. A. V. Demchenko, E. Rousson, G.-J. Boons, Tetrahedron Lett., 1999, 40, 6523-6526. 129. G. W. Griffin, N. C. Bandara, M. A. Clarke, W . 3 . Tsang, P. J. Garegg, S. Oscarson, B. A. Silwanis, Heterocycles, 1990,30, 939-947. 130. C. Amatore, A. Jutand, J.-M. Mallet, G. Meyer, P. Sinay, J. Chem. SOC.Chem. Commun., 1990, 718-719. 131. G. Balavoine, A. Greg, J.-C. Fischer, A. Lubineau, Tetrahedron Lett., 1990,31, 5761-5764. 132. A. Marra, J.-M. Amatore, C. Amatore, P. Sinay, SynLett., 1990, 572-574. 133. J.-M. Mallet, G. Meyer, F. Yvelin, A. Jutand, C. Amatore, P. Sinay, Carbohydr. Rex, 1993, 244,237-246, 134. Y.-M. Zhang, J.-M. Mallet, P. Sinay, Curbohydr. Res., 1992, 236, 73-88. 135. S. Mehta, B. M. Pinto, Carbohydr. Rex, 1998, 310, 43-51. 136. N. K. Kochetkov, E. Klimov, N. N. Malysheva, Tetrahedron Lett., 1989,30, 5459-5462. 137. N. K. Kochetkov, N. N. Malysheva, E. Klimov, A. V. Demchenko, Tetrahedron Lett., 1992, 33, 381-384. 138. A. Marra, L. K. S. Shun, F. Gauffeny, P. Sinay, Synlett, 1990, 445-448. 139. A. Marra, F. Gauffeny, P. Sinay, Tetrahedron, 1991, 47, 5149-5160. 140. A. Marra, P. Sinay, Carbohydr. Res., 1990, 195, 303-308. 141. H. Lonn, K. Stenvall, Tetrahedron Lett., 1992, 33, 115-116. 142. U. Ellervik, G. Magnusson, J. Orq Chem., 1998, 63, 9314-9322, 9223. 143. P. Fugedi, P. J. Garegg, S. Oscarson, G. Rosen, B. A. Silwanis, Carbohydr. Res., 1991, 211, 157-1 62. 144. S. Hashimoto, T. Honda, S. Ikegami, Tetrahedron Lett., 1990,31, 4769-4772. 145. H. Bielawska, M. Michalska, J. Curbohydr. Chem., 1991, 10, 107-1 12. 146. L. Laupichler, H. Sajus, J. Thiem, Synthesis, 1992, 1133-1136. 147. 0.J. Plante, P. H. Seeberger, J. Org. Chem., 1998,63, 9150-9151. 148. D. A. Leigh, J. P. Smart, A. M. Truscello, Carbohydr. Res., 1995, 276, 417-424. 149. F. Belot, J.-C. Jaquinet, Carbohydr. Res. 290, 1996, 290, 79-86. 150. D. R. Mootoo, P. Konradsson, U.Udodong, B. Fraser-Reid, J. Am. Chem. Soc., 1988, 110, 5583-5584. 151. N. L. Douglas, S. V. Ley, U. Lucking, S. L. Warriner, J. Chem. SOC.Perkin Trans. I , 1998, 51-65. 152. Z. Zhang, I. R. Ollman, X.-S. Ye, R. Wischnat, T. Baasov, C.-H. Wong, J. Am. Chem. SOC., 1999.121. 734-753. 153. A. K. Choudhury, I. Mukherjee, B. Mukhopadhyay, N. Roy, J. Carbohydr. Chem., 1999,18, 361-367. 154. S. Cao, F. Hernandez-Mateo, R. Roy, J. Carbohydr. Chem., 1998, 17, 609-631. 155. L. A. J. M. Sliedregt, K. Zegelaarjaarsveld, G. A. van den Marel, J. H. van Boom, Synlett, 1993, 335-337. 156. R. Roy, F. 0. Andersson, M. Letellier, Tetrahedron Lett., 1992, 33, 6053-6056. 157. M. Lahmann, S. Oscarson, unpublished results. 158. F. Baressi, 0. Hindsgaul, J. Am. Chem. SOC.,1991, 113, 9376-9377. 159. M. Bols, J. Chem. SOC.Chem. Commun., 1992,913-914. 160. F. Baressi, 0. Hindsgaul, Can. J. Chem., 1994, 72, 1447-1465. 161. Y. Ito, T. Ogawa, Ang. Chem. Int. Ed. Engl., 1994,33, 1765-1767. 162. C. Krog-Jensen, S. Oscarson, J. Org. Chem., 1998, 63, 1780-1784. 163. T. Ziegler, R. Lau, Tetrahedron Lett., 1995, 36, 1417-1420. 164. S. Valverde, A. M. Gomez, J. C. Lopez, B. Herradon, J. Chem. SOC.Chem. Commun., 1995, 2005-2006. 165. M. Miiller, U. Huchel, A. Geyer, R. R. Schmidt, J. Org. Chem., 1999, 64, 6190-6201. 166. K. C. Nicolaou, N. Winssinger, J. Pastor, F. DeRoose, J. Am. Chem. Soc., 1997,119,449-450. 167. K. C. Nicolaou, N. Watanabe, J. Li, J. Pastor, N. Winssinger, Angew. Chem. Int. Ed. Engl., 1998,37, 1559-1561.
Carbohydrates in Chemistry and Biology Beat Ernst, Gerald W. Hart, Pierre Sinay copyrightQ WILEY-VCH Verlag GmbH, 2000
5 Glycosylation Methods: Use of Phosphites Zhiyuan Zhang and Chi-Huey Wong
5.1 Introduction
In the chemical synthesis of oligosaccharides, the overall procedure can be divided into five steps: 1) design and preparation of the building blocks (glycosyl donors and acceptors) with selected protecting groups; 2) manipulation of the protecting groups to free the desired hydroxyl group; 3) separation of products after each step; 4) stereo-controlled glycosylation; and 5 ) deprotection and product purification. Of those steps, 1-3 are the most time-consuming. Considerable efforts have thus been made to facilitate the synthetic process. For example, many methods have been developed to reduce the number of steps in the synthesis of building blocks. Recently developed orthogonal protection-deprotection strategies [ 1, 21 provide the efficiency and flexibility for the preparation of highly diversified carbohydrate libraries [ 1, 31. To minimize protecting group manipulation, the armed-disarmed strategy [4], the orthogonal glycosylation strategy [ 5 ] , and the one-pot multiglycosylation strategy [6-81 have been developed. In terms of simplifying the purification procedure, solid-phase synthesis [91 and one-pot solution-phase synthesis [7d, 81 have shown great promise. Glycosylation is the central reaction of carbohydrate chemistry. Because low yield, low regioselectivity, and low stereoselectivity are frequently encountered, it is this step which requires special attention. Though chemists might be able to synthesize any oligosaccharide [lo],there is no universally employed glycosylation [ lOc, 111. Therefore, development of new and efficient methods of glycosylation is still quite challeng,ing.
118
5 Glycosylation Methods: Use of Phosphites
The use of glycosyl phosphite as a glycosyl donor was initiated in 1992. The Wong group [12] and the Schmidt group [13] independently reported that trimethylsilyl triflate (TMSOTf) could activate glycosyl phosphites in glycosylation reactions. An advantage of this method is that it provides a very high yield and aselectivity in the synthesis of sialic acid derivatives [12, 131. This method has been further developed by these two groups and others. Different promoters have been investigated and some unusual stereoselectivities have been reported. The purpose of this chapter is to review recent developments in phosphite glycosylation and its applications.
5.2 Preparation of Glycosyl Phosphites Glycosyl phosphites are prepared from their corresponding anomeric hydroxyl compounds, either by treatment with dialkyl N,N-diethylphosphoramidites (DDP) and 1,2,4-triazole [ 141 or with dialkyl phosphorochloridites in the presence of Hunig's base (Figure 1) [ 13, 151. Most phosphitylation reagents are commercially available, and both methods give glycosyl phosphites in high yield. Examples of glycosyl phosphites that can be prepared by these methods are dibenzyl phosphites, diethyl phosphites, and dimethyl phosphites. Bicyclic glycosyl phosphites such as 4 and 5 can also be prepared. In the synthesis of an N-acetyllactosamine (LacNAc) derivative it has been shown that 4 gives better yields than the corresponding trichloroacetimidate [ 14fl. When the sugar moiety is highly electron-donating, such as the 2,6-di-deoxy derivative, its diethyl phosphite derivative could not be prepared.
Et2N-P-(OBn),
PCH
A . d
I
COOMe
1,2,4-triazole AcO
1
CI-P-(0Et)2 EtNiPr2
4
3 97%
AcO
Figure 1.
COOMe
5.3 Glycosylotion using Glycosyl Phosphites
1 19
The corresponding pinacol phosphite 5 was, however, stable enough to be isolated in 67% yield [16]. Several phosphitylation reagents are now available for the preparation of glycosyl phosphites with desirable reactivity. Factors known to affect the anomeric ratio in the preparation of glycosyl phosphites include the anomeric composition of the starting hydroxyl compound. For example, a mixture of galactosyl phosphite with an a : ratio of 90 : 10 was obtained with an a : ratio of 90: 10. A different from 2,3,4,6-tetra-O-benzylgalactopyranose anomeric mixture ( a :p = 61 :39) of the phosphite product was, however, generated from an anomeric mixture of the galactopyranose ( a :p = 56:44) [17].2,3,4,6-Tetra0-acetylgalactose ( a :p = 3 : 1) and glucose ( a :p = 2: 1) gave the phosphite p isomer as a predominant product ( a :p = 1 :4 and 1 :2 respectively), whereas the 2-acetamido-2-deoxy sugar gave mainly the a-phosphite ( a :p > 7: 1) [18]. Surprisingly, only phosphite p isomers (2 and 3) were observed when sialic acid (NeuSAc) derivatives were phosphitylated using either phosphitylation method [ 12, 131. Solvents also affect the product composition. Phosphitylation of 2,3,4,6-tetra-Oacetylgalactose in CH2C12 gave the dibenzyl phosphite with an a : p ratio of 1 :2; this increased to 1 : 6 when THF was used as solvent [ 181. Effects of Lewis acid [ 191 and mild base [20] on the anomeric ratio of the phosphite have also been reported. In general the anomeric ratio of the phosphite does not have a large effect on the glycosylation step in terms of reactivity and stereoselectivity [ 171. It might, however, be a factor in the synthesis of phosphate derivatives from phosphites (see Section 5.4).
5.3 Glycosylation using Glycosyl Phosphites 5.3.1 Mechanism The first catalyst used to activate the glycosyl phosphite was TMSOTf [ 12, 131. The mechanism of the reaction has been investigated [12]. As shown in Figure 2, path a applies when TMSOTf is mixed with donor first or added into the mixture of donor and acceptor. In this method, the formation of a substantial amount of phosphonate orthoester is a considerable problem. As illustrated in path b, however, a premixed solution of TMSOTf and acceptor spontaneously generates triflic acid (TfOH). TfOH then activates the glycosyl phosphite added subsequently to give the desired product, and reduces the formation of the orthoester. The most facile method is through path c where TfOH directly catalyzes the glycosylation, and also reduces the nucleophilicity of the hydrogen phosphonate. TfOH is actually involved in each of the pathways, and is potentially the real catalyst even when TMSOTf is used [21]. In general, TfOH-catalyzed glycosylation gives the highest yield. Notably, addition of glycosyl phosphite to premixed TMSOTf and acceptor gave a better yield than addition of TMSOTf to the mixture of donor and acceptor [22]. In practice, however, it is more convenient to use TMSOTf than TfOH as catalyst. Interestingly, BF3.Et20-promoted [ 171 and TMSOTf-promoted [ 12, 13, 211 gly-
120
5 Glycosylation Methods: Use of Phosphites
a. TMSOTf reacts with donorfirst
-
TMSO-P(OBn)2
TMSOTf
HOTf
b. TMSOTfreacts with acceptorfirst
TMSOTf
TMSOR HO-P(OBn),
-
R
HP(OBn),
c. When TfOH was used
Figure 2.
cosylations using perbenzylated phosphites at low temperature (-78 "C), as reported by Hashimoto et al., gave similar stereoselectivity and yields. Both activation gave high 1,2-trans-P-selectivityeven without a participating group at the C-2 position of the glycosyl donor [ 171. BF3.EtzO-promoted glycosylations, furthermore, gave even better P-selectivity. The reason for this, and the nature of the intermediate involved in the BF3 .Et20-promoted glycosylation, remain unclear [ 171. More recently, the Hashimoto group developed a new activation method using 2,6-di-tert-butylpyridinium iodide (DTBPI) and tetrabutylammonium iodide (BmNI), and achieved high a-selectivity. The intermediate was found to be the aglycosyl iodide, which is first anomerized to the P isomer then glycosylated through a S~2-likemechanism (Figure 3). In general, a-selectivity is predominant in glycosylations using the phosphite method. Watanabe et al. [22] have investigated other Lewis acids as promoters of glycosylation using glycosyl phosphites; they found that ZnCl2, ZnCl2-AgC104, 12, and other Lewis acids can efficiently activate perbenzylated phosphites at room temperature. The stereoselectivities are generally lower than when reaction is performed out at low temperature. The effect of promoters on the glycosylation of perbenzylated glucosyl phosphite 6 with a primary alcohol was studied (Figure 4).ZnClz-
5.3 Glycosylation using Glycosyl Phosphites
121
60-95% cc/B > 90110
8 donors
Figure 3.
promoted glucosylation gave predominantly the P product, 7. In contrast, 12promoted reactions mainly gave the a product, whereas almost no selectivity was observed with the ZnClz-AgC104-promoted glycosylation [ 17b]. It is unclear why the addition of AgC104 would increase the efficiency and reduce the selectivity of the reaction. The origin of selectivity remains to be investigated [17b]. Metal perchlorate salts (e.g. LiC104), which act as weak Lewis acids, activate the glycosyl phosphite and yield the glycosyl perchlorate ion pair which leads to the product [23] This method provides a useful alternative when acid-labile protecting groups, or acid-sensitive glycosyl linkages are involved. The low yield and low stereoselectivity are potential drawbacks of this method. 5.3.2 Low Temperature-Dependent Stereoselectivity The stereoselectivity of a glycosylation is controlled by many factors, including the substituent at the C-2 position, the leaving group on the anomeric center, temperature, solvents, and the structural features both of glycosyl donor and acceptor. In the construction of a glycosyl P-linkage, a participating group at the C-2 position of the glycosyl donor is normally required. In the absence of this participating group the thermodynamically favorable a-glycosyl bond is generally formed because of the anomeric effect [24]. Thus, the stereo-controlled synthesis of the P-linkage is considered to be difficult. A solution to this problem is to use acetonitrile as solvent to provide the nitrile effect [25] to aid the formation of the P-linkage. In addition, some newly developed glycosylatioii methods using glycosyl donors with a non-participating group at the C-2 position at low temperature gave very high p-selectivities [17, 21, 22b, 26, 271. These methods include the use of sulfoxides activated with Tf20 [27, 281, glycosyl bromides activated with AgOTf [27], thioglycosides activated with RSCl-AgOTf
Lewis acid
Ph(CH&OH
B
%B
Lewis acid
6
+
BB& O(CH.&Ph
OP(O5h 7
Figure 4.
Yield
1,
92% 81/19
ZnCI,
88% 20180
ZnCI2-AgC1O4 92% 52/48
122
5 Glycosylation Methods: Use of Phosphites
I
Temp.
-78OC
-5OOC
8
3:97
8:92
11:89
1:99
2:98
3:97
-3oOc
8
BF3-Et20
Ratio
ROH
9
(b.) Watanabe eta/.
6 I
LNlS/TfOtJ CH2C12
-\
B"4 BnO 7
O(CH&Ph
3°C
-21 "C -45°C -68"C
Figure 5.
[27, 291 and glycosyl phosphites activated with TMSOTf [17, 211 or BF3.Et20 [17, 261. Low temperature seems to promote P-selectivity; the thermodynamically stable a-glycosyl triflate is formed and further reacted in a S~2-likemechanism with the added glycosyl acceptor to give the P-glycoside [27b, c]. Figure 5 shows the temperature-dependent selectivity reported by Hashimoto et al. [17] and Watanabe et al. [22b] Further study showed that P-selectivity was almost independent of solvent [ 171, although slightly dependent on the anomeric composition of the donor [17, 211. This is exemplified by the synthesis of Pgalactosyl-, P-glucosyl-, and P-glucuronyl linkages [ 14e, 16, 17, 21, 26, 301. Fucosyl phosphites behave differently under these conditions, however, and a-selectivity is predominant [21, 30, 311. The stereoselectivity issues of glycosyl phosphites will be discussed later.
5.3.3 Glycosylation of Sialyl Phosphites Sialylated oligosaccharides are often expressed on the surfaces of cells, including cancer cells, and are very attractive targets for investigation. Sialylation [ 321, especially yield and stereoselectivity, is, however, still a major problem in oligosaccharide synthesis. Synthetic difficulties stem from the tertiary-hindered anomeric center and the lack of an electron-demanding group adjacent to the anomeric center of sialylic acid (NeuAc) [ 121. Sialylation using sialyl phosphites is currently one of the most successful synthetic methods, and many sialylated compounds have been prepared by this strategy. Compounds 10-11 and 13 (see Figure 6) were prepared from dibenzyl phosphite 2 [12], and compounds 10, 12 and 13-14 were synthesized from diethyl phosphite 3 [13]. In the synthesis of sialyl Lewisa (sLea), a regioselec-
5.3 Glycosylution using Glycosyl Phosphites A
123
OOMe
AcO 10 80% (a:p6:1) from 2 70% (cx:p4:1) from 3
OMe
Ho
PcHN 11 48% only cx from 2
OpC
Ph
13 44% (a:p6:1)from 2
12 38% cx from 3
Figure 6.
tive coupling of the sialyl moiety to the 3-OH on the Gal unit of partially protected Lea gave the desired compound 14 in low yield (18%). Also isolated was 35% of the lactonized product 15 [33]. This lactone side-product 15 was isolated as the only product (37%) when the same acceptor and a different glycosyl donor and promoter were used [34].
5.3.4 Glycosylation of C-2-Acylated Glycosyl Phosphites In general, the 1,2-tuans P-glycosyl linkage is formed by use of a C-2 participating protecting group. Catalytic amounts of TMSOTf (0.5 equiv.) can promote the glycosylation of peracetylated glycosyl phosphites. Donors utilized include fucosyl phosphites, galactosyl phosphites, glucosyl phosphites, glucuronyl phosphites, and glucosaminyl phosphites. Reaction of these donors with different glycosyl acceptors yield the desired P-product with yields of 40-70% [21, 351. T h s method has also been used for the synthesis of some P-C-glycosides and P-S-glycosides [21, 301. A few side-reactions are, however, encountered when using this method; examples include the formation of glycosyl phosphonate orthoesters [21, 30, 361, which are less reactive intermediates, the ester transformation problem [21, 361, and in some instances the formation of silylated acceptor byproducts [21]. Side-reactions often depend on the type of catalyst used in the reaction. Perbenzoylated glucosyl phos-
124
5 Glycosylution Methods: Use of Phosphites
Oh
BzO 16 R' =Bn, R2,R3 = PhCH, %YO, a only 17 R' =R3 = Bn, R2= H, 73%, a:p1:1 18 R' =R2=H, R3= Bn 88%, p only
BzO 19
loo%, aonly
20 93%, ponly
Figure 7.
phite in the presence of BF3.Et20 (1 equiv.), for example, gave 24% of the phosphonate orthoesters whereas use of 1 equiv. TMSOTf at -50°C gave the desired 1,2 trans-p product in excellent yield, with no traces of the aforementioned byproducts [36]. Other promoters such as ZnC12, ZnC12-AgOTf, and metal perchlorate salts have not been used for the activation of acylated glycosyl phosphites. Stereo-controlled synthesis of fructofuranosides is regarded as a difficult problem, even with a participating group next to the anomeric center [36]. The study of TMSOTf-catalyzed glycosylation using fructofuranosyl phosphite showed that a- or P-selectivity was highly dependent on the properties of the acceptor (Figure 7) [36]. 5.3.5 Glycosylation with C-2-0-Benzylated Glycosyl Phosphites
The glycosylation reaction using glycosyl phosphites without a participating protecting group at C-2 is more complicated. The stereoselectivity seems to depend on many factors, including reaction temperature, the core structure of the glycosyl phosphite, and the properties of acceptors and the promoters. Glycosylation using Glucosyl Phosphites with a Benzyl Group at C-2 Glycosylution with 0-selectivity Glucosylation of a primary hydroxyl acceptor with perbenzylated glucosyl phosphite, promoted by TMSOTf at -78"C, gave nearly exclusively the P-product 8 (66%, a : P = 1 :99 in CH2C12; and 78%, a : P = 2: 99 in EtCN). The P-selectivity decreased, giving the anomeric mixture 9 (83%, a : P = 32: 68 in CH2C12; and 65%, a : f3 = 17:83 in EtCN) when a secondary alcohol acceptor was used [17, 211. Of the many promoters studied, BF3.Et20 gave products in the highest yield and Pselectivity, even with secondary hydroxyl acceptors (a:P = 5 :95) [ 171. ZnC12-promoted glucosylations [22] gave lower 0-selectivity than the lowtemperature procedure (TMSOTf or BF3.EtzO), most probably because of the higher reaction temperature. ZnC12-AgC104 [22] was, however, successfully employed in the total synthesis of paeoniflorin reported by Corey and Wu [37]. In this instance glycosylation of the very hindered acceptor 22 (a mixture of enantiomers) with perbenzylated glucosyl phosphite 21 gave the enantiomerically pure 23 (1 8%,
5.3 Glycosylation using Glycosyl Phosphites
'& B
TIP93
22
OP(OMe)2
BnO
BB *
ZnC12-AgClO4
21
x
Y
@
BnO
M
125
e TIPS3
23 18% enantiomeric pure p
Figure 8.
see Figure 8). This process was more successful than any other glycosylation method, including the TMSOTf-catalyzed phosphite procedure. Glycosylation with a-selectivity From the results discussed above it seems that glycosyl phosphites are not adequate glycosyl donors for the formation of a-glycosyl linkages. Despite this, glycosylations using the perbenzyl glucosyl phosphite donor, in the presence of I2 at room temperature, gave the a-glycosylated compounds 7 and 24 as major products. Glucosylation of a hindered acceptor with the glucosyl phosphite, under ZnCl2AgC104 conditions, gave 9 (88%, a : p = 7 : 3, see Figure 9) with lower selectivity [22b]. The best a-selectivity was achieved under DTBPI-Bu4NI conditions to give product 9 in a 95 : 5 a : p ratio. Glycosylation using Galactosyl and Fucosyl Phosphites with a Benzyl Group at C-2
0-Galactosylation using perbenzylated galactosyl dibenzyl phosphite, in the presence of TMSOTf or BF3.Et20 at -78"C, gave nearly pure products [17, 211. In addition, ZnC12-promoted galactosylation of secondary and primary alcohols using galactosyl diethyl phosphite gave the 0 product with selectivity (a: p 1 :4)in the same range as that obtained in glucosylations [22]. To achieve high a-selectivity, 60-acetyl galactosyl dibenzyl phosphite 25 was used to regioselectively glycosylate the 3-0-position of a partially protected acceptor in CH2C12 at - 15"C to give predominantly product 26 in 60% yield (Figure 10) [30]. Fucosylation using fucosyl dibenzyl phosphites has been reported in the synthesis of Lea and Ley catalyzed by TfOH [31]. The phosphite and trichloroacetimidate
s
-
BnO B
O(CH&Ph 7 92%, a l p = 81/19
Figure 9.
24 91%, a@ = 81/19
9 88%, cr/p = 69/31
5 Glycosylution Methods: Use of Phosphites
126
TMSOTf
(0.2equiv) -15"C
B
oP(ow2
25
BB g E # %
b
OBl
60%
HO 26 cL/p = 85/15
Figure 10.
methods have been compared for the synthesis of Lea (Figure 1 1 ) [35].It was concluded that 0-glycosyl phosphites nicely complement 0-glycosyl trichloroacetimidates, especially in the higher reactivity range where trichloroacetimidates tend to be less stable. In the course of development of sialyl LewisXmimetics, the Wong group conducted extensive studies on the fucosylation of more than ten different N-acylated p-hydroxyl amino acids. They found that fucosylation of benzyl-protected amino acids with perbenzylated fucosyl phosphite gave a greater yield and better aselectivity than the corresponding ethyl-protected amino acids [30, 311. Figure 12 depicts representative syntheses of these compounds. In addition, the DTBPIBWNI-promoted fucosylation reported by Hashimoto's group also gives excellent a-selectivity [ 17b]. Glycosylation using other Glycosyl Phosphites with a Benzyl Group at C-2
The perbenzylated glucuronyl phosphite has shown preference for 1,2-truns-Pselectivity, similar to that of glucosyl phosphite, when coupled with primary and secondary alcohols in the presence of BF3.Et20 at -65°C [22]. Synthesis of the fi-mannosyl linkage is a major problem in glycosylation reactions. Many efforts have been made to improve the p-selectivity of mannosylation using, for example, insoluble Ag silicate in glycosylation [38],inversion at the C-2 of p-glucosyl derivative after glycosylation [391, and intramolecular glycosylation methods [40].Recently, p-mannosylation was also acheved at low temperature through the triflate intermediate which is generated by different activation methods [27](see Section 5.3.2). A similar result might be expected from activation of mannosy1 phosphite with TMSOTf or TfOH, because it might proceed through the
A Ac
E
x TMSOTf
____)
Et20 A
AcO 27 X = OP(OCH$CI& 28 X = OC(NH)CC13
Figure 11.
sRq
OBl
TMSOTf
___)
OTDS EtpO
opc 29 64%
88%
N3
AC
Opc
30 88% 78%
5.3 Glycosylution using Glycosyl Phosphites
127
3 2 H 2 1 L
-
BocH
31
CHJ
TfOH, CH2Cl2, -15 "C
OP(QW2
33 84% R= Bn, c(/p=99/1 34 72% R= Et,dD=71/29
Figure 12.
glycosyl triflate intermediate. Indeed, the Hashimoto group recently showed that 2,3-di-O-benzyl-4,6-O-benzylidine-mannosyl diethylphosphite preferentially gives P-selectivity [ 17~1,although ZnCl2- or ZnClz-AgC104-catalyzed mannosylations from the glycosyl phosphites have been reported to afford a- or P-selectivity. When the perbenzylated mannosyl phosphite is glycosylated with cyclohexanol under ZnCl2 conditions, slight preference for the p-anomeric linkage (83%; a : P 2 : 3 ) is obtained. When the glycosylation is performed with methyl 2,4,6-tri-O-benzyla-glucopyranoside and ZnClz-AgCIO4 activation, the product is pure a-linked disaccharide in 76% yield [22]. The phosphite method has also been used in the synthesis of di-mannosylated phosphatidylinositol with two a-glycosyl linkages, as shown in Figure 13. In the first glycosylation, ZnClz-AgC104 was used to activate perbenzylated glycosyl phosphite to give a 2: 1 alp mixture of 36a. The same conditions gave the pure a product 36b in 70% yield when a 2-OAc mannosyl phosphite was used as donor. Interestingly, at room temperature TMSOTf-catalyzed mannosylation using the perbenzylated phosphite gave a-glycoside 37 in 74% yield [41]. It is not clear how the temperature affects the stereoselectivity of glycosylations employing benzylated mannosyl phosphite with TMSOTf or TfOH as promoter. N
5.3.6 Glycosylation with 2-Deoxy Glycosyl Phosphites The synthesis of 2-deoxy oligosaccharides with controlled a- or P-selectivity remains a difficult problem [lOc, 421 and many methods have been developed to solve it.
@-
ZnC12AgC104
P
"'OH Et20
TIP<S
OH RO
35
Figure 13.
oh
36a: R=Bn 65% a:p2:1 36b: R=Ac 70% a only
5 Glycosylation Methods: Use of Phosphites
128
D-A Temp. Yield a:O
38-43 -78 "C 91% 19:81 38-43 -50
"C
87% 29:71
39-43 -94
"c
93% 13187
40-43 -94
"C 97% 1436
41-43 -94 "C 95% 23:77 42-43 -94 "C 96% 67:33 41-44 -94 "C 86% 69:31
38
39
40
Bn9 ,ow B
w (EtOhPO F
41
OH
BBs%q
43
44
B* OMe
Figure 14.
Examples include electrophile-mediated addition of acceptor to glycals [42a], and glycosylation of the C2-substituted glycosyl donor [42b] followed by reductive removal of the C-2 substituent [ lOc]. Direct stereoselective glycosylation using a 2deoxy glycosyl donor is, however, desirable. 'Remote-controlled' [43] activation of the 2-pyridine-thioglycoside by AgOTf [44]provides a very efficient method for the a-selectively controlled synthesis of 2-deoxy glycosides. Use of insoluble silver silicate for the activation of 2-deoxy glycosyl halides provides one of the best methods of preparation of 2-deoxy-0-glycosides [45]. The Schmidt group has studied the glycosylation reaction using 2-deoxy glycosyl phosphites activated by BF3 .Et20 in CH2Cl2-hexane or in Et20 [36]. Preferential a-selectivities were obtained in the formation of both the 2-deoxy galactosyl linkage and the 2-deoxy glucosyl linkage. In the glycosylation of 2-deoxy glycosyl phosphites under TMSOTf activation [12, 131, the Hashimoto group [26] recently found that the reaction temperature is crucially important in the control of P-selectivity (see Figure 14, entries 1-3). The selectivities were not significantly affected by the reactivities of the glycosyl donors (entries 1, 4, and 5; a :P = 10: 90, 13 :87, and 14: 86, respectively). They are, however, affected by other structural properties of the glycosyl donors. For example, compounds 41 and 42 with axial substituents at C-4 gave lower p-selectivities (entry 6, a : P = 23: 77 and entry 7, a : P = 67: 33). The p-selectivity was observed to increase with increasing reactivity of the acceptor alcohol (compare entries 6 and 8). In the synthesis of the hexasaccharide fragment of landomycin A, the desirable p-glycosyl linkage of the 2,6-dideoxy unit was successfully formed by use of the TMSOTf-promoted phosphite method (Figure 15) [ 161.
5.4 Other Applications of Glycosyl Phosphites Besides the 0-,S-, C-glycosylations and 0-glycopeptide synthesis discussed above, other applications of glycosyl phosphites are discussed below.
5.4 Other Applications of Glycosyl Phosphite
129
TMSOTf -94 OC AcO
HO
c,
AcO
47
&*+
OMP
TMSOTf, Toluene,
0 M
48 R' = AC (42%, a:p 5 2 ~ 8 )
A d
Figure 15.
5.4.1 Synthesis of CMP-NeuAc
The synthesis of CMP-NeuSAc remains of interest, because it is a glycosyl donor in glycosyltransferase-catalyzed reactions. Three chemical synthetic methods based on the phosphite strategy have been reported. The Wong group employed a glycosyl phosphoamidate (Figure 16A) [12], whereas the Halcomb group used a nucleoside phosphoamidate in the synthesis of CMP-NeuSAc (Figure 16B) [46a]. The latter method seems preferable, because of its high-yielding deprotection step. The Schmidt group utilized the diethyl glycosyl phosphite and the nucleoside phosphate 53 in its acid form to give P-CMP-NeuAc 54 in 50% yield (Figure 17) [46b].The reaction seems to be mediated by acid catalysis.
5.4.2 Synthesis of GDP-Fucose
GDP-fucose is a glycosyl donor substrate for fucosyltransferases. Although it has been synthesized by many chemical methods [47],the use of fucosyl phosphite in the synthesis seems the most practical [48]. A recent improvement of this method includes the addition of tetrazole to the morpholidate coupling reaction [48b]. This method might also be applicable to the synthesis of other nucleoside diphosphate sugars (Fig-ure 18). Together with the synthesis of CMP-NeuSAc discussed above, glycosyl phosphite chemistry indeed provides a useful alternative for the synthesis of natural and unnatural donor substrates for the study of enzyme-catalyzed glycosylations.
130
5 Glycosylation Methods: Use of Phosphites NHBz 1. HOR 2. BuOOH 12 Yo
50
51
52
Figure 16.
HQ
PH
HAC
CH ,CN/TH FIDMF
0 3
AcO 01% 53
(1:l:l)
-15 "C to rt.,
AcO AcO 54 50%
Figure 17.
1.30% H202 2. H2IPd-C F 0 $ O N a h AcO F z z B n 0 ) 2 3. NaOWH20 HO OH 55 63% 54 cr:p =1:10 tetrazolej Pyr
57 91%
Figure 18.
Ho
OH
OPC
5.4 Other Applications of Glycosyl Phosphite Ac
131
TMSOP(OMe)* TMSOTf CHzCI2
PCH
A d
ACQ 58 63 Yo Ponly
3 Figure 19.
5.4.3 Formation of Glycosyl Phosphonate Glycosyl phosphites can be converted by Arbuzov-type fragmentation to the corresponding glycosyl phosphonates as analogs of glycosyl phosphates [49]. Glycosyl phosphonates are more stable than glycosyl phosphates [50]and can act either as inhibitors [5I] or as regulators in metabolic processes where natural phosphates function. Figure 19 shows the synthesis of a sialyl phosphonate starting from the glycosyl phosphite [52]. 5.4.4 Transformation to other Types of Glycosyl Donor Phosphate Oxidation [I 8, 481 of glycosyl phosphites provides glycosyl phosphates which have been used for the synthesis of oligosaccharides [53] and sugar nucleosides [12, 81 (Figure 20).
rA-OP(ORh
oxidation
8
* a O F ' ( O R h
HOR TMSOTf
OR
Figure 20.
Phosphorimidate More recently, a new glycosylation method has been reported using glycosyl phosphorimidates as glycosyl donors. Thus, compounds were prepared from the corresponding glycosyl phosphites (Figure 21) 1541.
Figure 21.
132
5 Glycosylation Methods: Use of Phosphites
In summary, use of glycosyl phosphites in a new glycosylation method has received much attention for several reasons, including the high reactivity of the glycosyl phosphite at low temperature, the high efficiency of glycosylation with stereo-hindered donors or acceptors, and the high stereoselectivity of the reaction. Applications of glycosyl phosphites in the synthesis of glycosyl phosphates and glycosyl phosphonates are, furthermore, especially useful. Applications and modifications of glycosyl phosphite chemistry will surely be of interest to many chemists in the future.
References 1. Wong, C.-H., Ye, X.-S., and Zhang, Z . J. Am. Chem. SOC.1998,120, 7131. 2. T. Wubberg, C. Kallus, T. Opatz, S. Henke, W. Schmidt, H. Kunz, Angew. Chem. Int. Ed. Engl. 1998,37, 2503-2505. 3. Random glycosylation: (a) 0. Kanie, F. Barresi, Y. Ding, J. Labbe, A. Otter, L. S. Forsberg, B. Ernst, 0. Hindsgaul, Angew. Chem. Znt. Ed. Engl. 1995, 34, 2720. (b) Y. Ding, J. Labbe, 0. Kanie, 0. Hindsgaul, Bioorg. Med. Chem. 1996, 4, 683. Latent-active glycosylation: G.-J. Boons, B. Heskamp, F. Hout, Angew. Chem. Znt. Ed. Engl. 1996,35,2845. Solid-phasemethod: R. Liang, L. Yan, J. Loebach, M. Ge, Y. Uozumi, K. Sekanina, N. Horan, J. Gildersleeve, C. Thompson, A. Smith, K. Biswas, W. C. Still, D. Kahne, Science 1996,274, 1520. 4. (a). D. R. Mootoo, P. Konradsson, U. Udodong, B, Fraser-Reid, J. Am. Chem. SOC.1988,110, 5583; (b). B, Fraser-Reid, Z. Wu, U. D. Udodong, H. Ottosson, J. Urg. Chem. 1990, 55, 60686070. 5. Y. Ito, T. Ogawa, J. Am. Chem. SOC.1994,116, 12073. 6. (a). S. Raghavan, D. Kahne, J. Am. Chem. SOC.,1993,115, 1580. (b) H. Yamada, T. Harada, H. Miyazaki, T. Takahashi, Tetrahedron Lett., 1994, 35, 3979. (c) H. Yamada, T. Harada, T. Takahashi, J. Am. Chem. SOC.1994, 116, 7919. (d) H. K. Chenault, A. Castro, Tetrahedron Lett., 1994, 35, 9145. (e) R. Geurtsen, D. S. Holmes, G.-J. Boons, J. Urg. Chem. 1997, 62, 8145. 7. (a) S. V. Ley, H. W. M. Priepke, Angew. Chem. Int. Ed. Engl. 1994,33,2292. (b) P. Grice, S. V. Ley, J. Pietruszka, H. W. M. Priepke, E. P. E. Walther, Synlett 1995, 781. (c) P. Grice, S. V. Ley, J. Pietruszka, M. I. Osborn, W. M. Henning, H. W. M. Priepke, S . L. Warriner, Chem. Eur. J. 1997, 431. (d). N. L. Douglas, S. V. Ley, U. Lucking, S. L. Warriner, J. Chem. Soc. Perkin Trans. 1, 1998, 51. (e). L. Green, B. Hinzen, S. J. Ince, P. Langer, S. V. Ley, S . L. Warriner, Synlett. 1998, 4, 440. 8. Z. Zhang, I. R. Ollmann, X.-S. Ye, R. Wischnat, T. Baasov, C.-H. Wong, J. Am. Chem. SOC. 1999, 121, 734. 9. Solid-phase synthesis: For review see, (a). P. H. Seeberger, S. J Danishefsky, Acc. Chem. Res. 1998, 31, 685. (b). J. S. Fruechtel, G. Jung, Angew. Chem., Int. Ed. Engl. 1996, 35, 17; For general articles see, (c) M. J. Sofia, Comb. Chem. Mol. Diversity Drug Discovery, Eds: E. M. Gordon, J. F. Kenvin Jr., Wiley-Liss, New York, 1998, 243-269; (d). R. R. Schmidt, Pure Appl. Chem. 1998, 70, 397-402; (e). Z.-W. Guo, Y. Nakahara, Y. Nakahara, T. Ogawa, Angew. Chem., Znt. Ed. Engl. 1997, 36, 1464; (f). R. Rodebaugh, S. Joshi, B. Fraser-Reid, H. M. Geysen, J. Org. Chem. 1997, 62, 5660; (8). S. J. Danishefsky, K. F. McClure, J. T. Randolph, R. B. Ruggeri, Science 1993,260, 1307; For enzymatic methods see, (h). M. Schuster, P. Wang, J. C. Paulson, C.-H. Wong, J. Am. Chem. SOC.1994,116, 1135. 10. For the recent review articles on oligosaccharide synthesis see: (a) H. Paulsen, Angew. Chem. Int. Ed. Engl., 1990, 29, 823; (b) J. Banoub, Chem Rev. 1992, 92, 1167; (c) K. Toshima, K. Tatsuta, Chem. Rev. 1993, 93, 1503. (d) R. R. Schmidt, W. Kinzy, Adv. Carbohydr. Chem. Biochem. 1994, 50, 21. (e) S. J. Danishefsky, M. T. Bilodeau, Angew. Chem. Int. Ed. Engl., 1996,35, 1380. 11. H. Paulsen Angew. Chem. Int. Ed. Engl., 1982,21, 155.
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12. H. Kondo, Y. Ichikawa, C.-H. Wong, J. Am. Chem. SOC.1992,114, 8748. 13. T. J. Martin, R. Schmidt, Tetrahedron. Lett. 1992, 33, 6123. 14. (a). L. I. Smirnova, M. A. Malenkovskaya, D. A. Predvoditelev, E. E. Nifantev, Zh. Org. Khim. 1980, 16, 1170; (b). J. W. Perich, R. B. Johns, Tetrahedron Lett. 1987,28, 101; (c). K. L. Yu, B. Fraser-Reid, Tetrahedron Lett. 1988, 98, 979; (d). R. L. Pederson, J. Esker, C.-H. Wong, Tetrahedron, 1991, 47, 2643; (e). S. Aoki, H. Kondo, C.-H. Wong, Methods in Enzymology, 247, 193; (f). Qiao, B. W. Murray, M. Shimazaki, J. Schultz, C.-H. Wong, J. Am. Chem. SOC. 1996, 118, 1653. 15. H. Paulsen, H. Tietz, Carbohydr. Res. 1984, 125, 47. 16. Y. Guo and G. A. Sulikowski, J. Am. Chem. SOC.1998,120, 1392. 17. (a). S. Hashimoto, K. Umeo, A. Sano, N. Watanabe, M. Nakajima, and S. Ikegami, Tetrahedron Lett., 1995,36, 2251; (b). H. Tanaka, H. Sakamoto, A. Sano, S. Nakajima, S. Hashimoto, Chem. Commun., 1999, 1259; (c). unpublished result, personal communication with Prof. Hashimoto. 18. M. M. Sim, H. Kondo and C.-H. Wong, J. Am. Chem. SOC.1993,115,2260. 19. R. R. Schmidt, B. Wegmann, K.-H. Jung, Liebigs Ann. Chem. 1991, 191, 121. 20. S. Sabesan, S. Neira, Carbohydr. Res. 1992, 223, 169. 21. H. Kondo, S. Aoki, Y. Ichikawa, R. L. Halcomb, H. Ritzen, C.-H. Wong, J. Org. Chem. 1994, 59, 864. 22. (a). Y. Watanabe, C. Nakamoto, S. Ozaki, Synlett, 1993, 115-116; (b). Y. Watanabe, C. Nakamoto, T. Yamamoto, S. Ozaki, Tetrahedron, 1994, 50, 6523. 23. H. Schene, H. Waldmann, Eru. J. Ory. Chem. 1998, 1227. 24. Lemieux Abstr: Pap. Am. Chem. SOC.1958. 133, 31N; (b) J. P. Praly, R. U. Lemieux, Can. J. Chem. 1987,65,213. 25. (a). R. R. Schmidt, M. Behrendt, A. Toepfer, Synlett, 1990, 694; (b). A. J. Ratcliffe, B. FraserReid, J. Chem. Soc., Perkin Trans. 1 1990, 747; (c). P. Sinay, Pure Appl. Chem. 1991, 63, 519. 26. S. Hashimoto, A. Sano, H. Sakamoto, M. Nakajima, Y. Yanagiya, S. Ikegami, Synlett., 1995, 1271. 27. (a). D. Crich, S . Sun, J. Ory. Chenz. 1996, 61, 4506-4507: (b). D. Crich, S . Sun, J. Am. Chem. SOC.1997, 119, 11217; (c). D. Crich, S. Sun, J. Am. Chem. SOC.1998, 120, 435. 28. (a). D. Kahne, S. Walker, Y. Cheng, D. V . Engen, J. Am. Chem. SOC.1989, 111, 6881; (b). L. Yan, D Kahne, J. Am. Chem. SOC.1996, 118, 9239. 29. (a). V. Martichonok, G. Whitesides, J. Am. Chem. SOC.1996, 118, 8187; (b). V. Martichonok, G. Whitesides, J. Org. Chem. 1996, 61, 1702. 30. C.-C. Lin, M. Shimazaki, M.-P. Heck, S. Aoki, R. Wong, T. Kimura, H. Ritzen, S. Takayama, S.-H. Wu, G. Weitz-Schmidt, C.-H. Wong, J. Am. Chem. SOC.1996, 118, 6826. 31. S.-H. Wu, M. Shimazaki, C.-C. Lin, L. Qiao, W. J. Moree, G. Weitz-Schmidt, C.-H. Wong, Angew. Chem. Int. Ed. Engl., 1996, 35, 88. 32. For sialylations see ref. 12, and 13 and references therein. 33. N. E. Nifantev, Y. E. Tsvetkov, A. S. Shashkov, L. 0. Kononov, V. M. Menshov, A. B. Tuzikov, a n d N . V. Bovin, J. Carbohydr. Chem. 1996, 15, 939. 34. U. Sprengard, G. Kretzschmar, E. Bartnik, C. Hiils, and H. Kunz, Angew. Chem. lnt. Ed. Engl. 1995, 34, 990. 35. T. Muller, G. Hummel, R. R. Schmidt, Liebigs Ann. Chem. 1994, 325. 36. T. Miiller, R. Schneider, R. R. Schmidt, Tetrahedron Lett. 1994,35,4763. 1993, 115, 8871. 37. E. J. Corey, Y.-J. Wu, J. Am. Chem. SOC. 38. H. Paulsen, 0. Lockhoff, Chem. Ber. 1981,114, 3102. 39. H. Kunz, W . Giinther, Angew. Chem. Int. Ed. Engl. 1988, 27, 1086. 40. (a). F. Barresi, 0. Hindsgaul, J. Am. Chem. SOC.1991, 113,9376; (b). G. Stork, G. Kim, J. Am. Chem. SOC.1992, 114, 1087; (c). Y. Ito, T. Ogawa, J. Am. Chem. Soc. 1994, 116, 12073. 41. (a). Y. Watanabe, T. Yamamoto and S. Ozaki, J. Org. Chem. 1996,61, 14-15; . (b). Watanabe, T. Yamamoto and S. Ozaki, Tetrahedron, 1997, 53, 903. 42. (a). J. Thiem, W. KlaKke, Top. Curr. Chem. 1990, 154, 870; (b). William Roush and Chad E. Bennett J. Am. Chem. SOC. 1999, 121, 3541. 43. S. Hanessian, C. Bacquet, N. Lehong Carbohydr. Res. 1982, 80, c17. 44. Z. Zhang, G. Magnusson, Carbohydr. Res. 1994,262, 79.
134
5 Glycosylation Methods: Use of Phosphites
45. (a). P. J. Garregg, S. Kopper, P. Ossowski, J. Thiem, J. Carbohydr. Chem. 1986, 5, 59; (b). R. W. Binkley, D. J. Koholic, J. Org. Chem. 1989, 54, 3577; (c). Z. Zhang, G. Magnusson, J. Org. Chem. 1996,61, 2383. 46. (a). M. D. Chappell, R. L. Halcomb, Tetrahedron 1997, 53, 11109; (b). T. J. Martin, R. R. Schmidt, Tetrahedron Lett. 1993, 34, 1765. 47. U. B. Gokhale, 0. Hindsgaul, M. M. Palcic, Can. J. Chem. 1990, 68, 1063; (c). R. R. Schimidt, B. Wegmann, K.-H. Jung Liebigs. Ann. Chem. 1991,191, 121. 48. (a). Y. Ichikawa, M. M. Sim, C.-H. Wong, J. Org. Chem. 1992, 57, 2943-2946; (b). V. Wittmann, C.-H. Wong J. Org. Chem. 1997, 62, 2144. 49. R. Meuwly, A. Vasella, Helv. Chim. Acta. 1986, 69, 25. 50. (a). J. Gao, V. Martichonok, G. M. Whitesides, J. Org. Chem. 1996, 61, 9538; (b). T.-H. Chan, Y.-C. Xin J. Org. Chem. 1997, 62, 3500; (c). B. Miiller, T. J. Martin, C. Schaub, R. R. Schmidt, Tetrahedron Lett. 1998, 39, 509; (d). M. J. Ruira, M. J. Pkrez-Pkrez, Jan. Balzaerini, M. Camarasa, Synlett. 1998, 177. 51. C. L. White, M. N. Janakiraman, W. G. Laver, C. Philippon, A. Vasella, G. M. Air, M. Luo, J. Mol. Biol. 1995,245, 623. 52. M. Imamura, H. Hashimoto, Tetrahedron Lett. 1996, 37, 1451. 53. S. Hashimoto, T. Honda, S. Ikegami, J. Chem. Soc. Chem. Commun. 1989, 685. 54. (a). S. Pan, H. Li, F. Hong, B. Yu, K. Zhao, Tetrahedron. Lett. 1997, 38, 6139; (b). H. Li, M. Chen, K. Zhao, ibid., 1997,38, 6143.
Carbohydrates in Chemistry and Biology Beat Ernst, Gerald W. Hart, Pierre Sinay copyrightQ WILEY-VCH Verlag GmbH, 2000
6 Glycosylation Methods: Use of n-Pentenyl Glycosides Bert Fraser-Reid, G. Anilkumar, Mark R. Gilbert, Subodh Joshi, and R a y Kraehmer
6.1 Introduction The use of protecting groups in syntheses of complex oligosaccharides is currently inevitable. Electronic or steric factors may enable regioselectivity between competing hydroxyl groups, but for the foreseeable future such interventions will be exceptions to the rule. If protecting groups are to be necessary, it would be advantageous for them to serve additional roles. In our laboratory this concept was first appreciated with the development of n-pentenyl glycosides (NPG), in which the pentenyl group protects the sensitive anomeric center, and survives (most of) the chemical transformations tolerated by normal alkyl glycosides. Treatment with an electrophile converts the pentenyl moiety into a leaving group, however, thereby enabling replacement reactions to occur at the anomeric center. This dual protection/activation role is a fundamental property of NPGs, and this duality was heavily exploited in the synthesis of the rat brain Thy-1 glycosylphosphatidylinositol membrane anchor by the retrosynthetic plan outlined in Scheme 1 [I]. NPGs have, however, also been valuable in mechanistic investigations designed to probe events at the anomeric center. For example, NPGs were instrumental in the demonstration that protecting groups can profoundly alter reactivities of glycosyl donors-and glycosyl acceptors. These observations indicated the importance of fine-tuning reactivity of donor/acceptor partners, and efforts to contribute to this insight continue in our laboratory.
6.2 Fundamental Reactions A summary of (most of) the fundamental reactions of n-pentenyl glycosides is presented in Scheme 2 [ 2 ] .Being simple alkyl glycosides, NPGs can be readily prepared
6 Glycosylation Methods: Use of n-Pentenyl Glycosides
136
V
0
HO
HO-
-
Thy1 Anchor from Rat Brain
OBn BnO
Scheme 1. Retrosynthetic plan for rat brain Thy-1 GPI membrane anchor.
by standard Fischer glycosidations, e.g., 4 4 5 . Where one or other anomer is specifically required, however, the standard procedures used for simple alkyl glycosides can be applied as summarized in Scheme 3. The role as glycosyl donor proceeds through the standard oxocarbenium intermediate 2, which can be trapped by nucleophiles. In aqueous medium the product is an aldose (1, Nu = OH). When such oxidative hydrolyses were probed it was found that with C2-OAcyl substrates the reaction occurs much more slowly than with C2OAlkyl. This observation has been introduced into a chemoselective coupling [3] protocol that has come to be known as the 'armed-disarmed strategy.' [4]Thus as illustrated in Scheme 4a, the partners 10 and 11 gave disaccharide 12a, with no evidence of the product of self-coupling of 11, nor of further reaction of disaccharide 12a with the acceptor 11, both of which would have occurred at disarmed anomeric
RN"& p-1 Y
1 Nu = OR, OSugar, Br, NHCOPeptide
/
6.2 Fundamental Reactions
p!
Y
Y
2
3 furanylium ion
glycosyl donor
137
J
6
free sugar
NPG
I disaccharide or higher
Zn or Smlp or Nal
glycosyl acceptor
cyclic halonium
I
+
XsNu'
9 bromohydrin Nu=OH dibromide Nu=Br
Scheme 2. The chemistry of n-pentenyl glycosides (NPG).
centers. Transformation to the armed counterpart 12b, however, enabled ready formation of trisaccharide 13 [3]. Glycoside hydrolysis is of immense mechanistic interest because of the insight it provides into enzymatic cleavage or assembly of oligosaccharides [5, 61. The option of oxidative hydrolysis meant that the anomeric center of NPG could be cleaved without the use of acids and, furthermore, that acid-labile protecting groups could be employed to enhance mechanistic insight. In the course of such investigations, it became clear that frequently used cyclic protecting groups could also deactivate glycosyl donors [7]. Thus, the advantage of simultaneous protection of two hydroxyl groups might be offset by the torsional constraints imposed upon the bicyclic array. Theoretical calculations supported this finding [81.
138
(Hqn-k>0H
6 Glycosylution Methods: Use of n-Pentenyl Glycosides
camphor Pent-OH
(HO)n{>O(/
sulfonic acid
I
OPent
Scheme 3. Preparative routes to NPG.
The reality of torsional armed-disarmed effects was demonstrated (Scheme 4b) with the glucosides 14 and 15, which gave the product of cross coupling, 16, but with no evidence of 17, the product from self-coupling of 15 [9].
6.3 Determination of Relative Reactivities The evidence in Scheme 4 makes it clear that success in oligosaccharide coupling can be dependent on protecting groups present on the reactants. A procedure for direct comparison of glycosyl donor reactivity would be advantageous, and such a methodology was therefore developed [lo]. As shown in Figure 1, eq. (l), equivalent amounts of the two NPGs, S1 and S2, compete for one equivalent of NBS in aqueous solvent. As eq. (2) shows the method requires that the NBS must be completely consumed, and so the reaction must continue until a negative test is obtained with potassium iodide-starch paper, shown independently to be accurate to within 2%. Because both anomers are in the same reaction medium, the NBS terms in the rate expressions cancel out, leading eventually to eq. (3). After work-up, the ratio of unreacted NPGs in the crude reaction product is determined, eq. (4). For our purposes, HPLC was convenient for these determinations. All the terms in eq. ( 5 ) are now known or knowable. And so the relative reactivity, kl/k2, of the two NPGs can be obtained by solving eq. (3). Some comparisons of reactivities, as determined by the procedure in Figure 1, are assembled in Scheme 5. That the choice of anomeric configuration of the donor might be important is apparent from the results for 18 and 19. In both the anomer
6.3 Determination of Relative Reactivities
k M
J+
0
,""I?,..
b T a
9
139
6 Glycosylation Methods: Use of n-Pentenyl Glycosides
140
S1
+ S2 + NBS
H20 ,Products CH,CN
(1 eq. of each) [end point determined by negative KI-starch test paper]
Figure 1. Calculating the relative rates of two glycosyl donors.
reacts more quickly, the higher ratio in 19 being evidence of anchimeric assistance resulting from neighboring-group participation in the cleavage reaction [ 1I]. The classical electronic armed-disarmed situation (Scheme 4a) is seen with the p glycosides 20a and b. Notably, 20b is less reactive than 20a despite the anchimeric assistance which must be occurring in the ester (cf 19). The results for the p glucoside pairs 20 and 21 confirm that the benzylidene ring can be disarming-much more so for acyl protecting groups (21, R = Ac compared with R = Bn). Couplings involving benzylidinated or acetonated donors might, therefore, occur less readily than with their torsion-free counterparts.
BnO
OPent
AcO
,OAc
OBn 18
OPent
R:)ope,,
= 1.59
OR
20
19
18p/ M a = 1.70
20d20b
\
a R=Bn
19p/ 19a= 5.19
b R=Ac R RO o R ~ O F ’ e n pl
~
~
~
~2 0 d 2 l a O = 1.6
\
OR
OK
20
21
a R=Bn
a R=Bn
b R=Ac
b R=Ac
Scheme 5. Relative reaction rates for some glycosyl donors.
F20b/ 2lb m= 10.4
6.4 n-Pentenyl Orthoesters as Glycosyl Donors
141
Although these results are based on NPG, they should apply equally to any pair of donors, irrespective of the anomeric leaving group. This assumption is based on general relevance of armed-disarmed factors across the spectrum of glycosyl donors 1121.
6.4 n-Pentenyl Orthoesters as Glycosyl Donors Alkyl orthoesters, 23, like cyclic acetals, also simultaneously protect two hydroxyl groups. Their use in carbohydrate synthesis [13] is greatly enhanced by a regioselective, acid-catalyzed rearrangement, whereby the resulting ester is axial rather than equatorial [ 141. Glycosyl (or 1,2-) orthoesters are readily prepared by Lemeiux’s procedure, in which acylated glycosyl bromides are treated with a hindered base, 22 23 [ 151 (Scheme 6). Mild acid treatment causes a rearrangement, 23 -, 26, in which the alkoxy unit is transferred to the anomeric center [16] (Scheme 6). The group so transferred can vary from simple alkoxy to an oligosaccharide [ 171. n-Pentenyl orthoesters (23, S = Pent) have an additional mode of reaction. Thus, treatment with an electrophile leads to furanylium ion 27, and thence to the same dioxolenium intermediate 25 (Scheme 6). The discharged entity, 28, however, is not nucleophilic and so a nucleophile present in the reaction medium faces no competition for reaction with 25 leading to 29. Notably, 26c and 29a are both higher saccharides, but the strategies for their preparation offer a choice between protonand electrophile-driven reactions. Again, n-pentenyl orthoester 23 (S = Pent) and NPG 26b are both glycosyl donors, but they have very different properties, notably towards acids. Further donor versatility comes from the fact that titration with bromine affords bromide 29b, the classic glycosyl donor, ready for reaction with silver triflate [ 181. To go from one glycosyl bromide to another, 22 +29b, might seem redundant, but the advantage of this possibility is readily appreciated from Scheme 7, which summarizes two approaches to trimannan 36, a building block for a synthesis of the Thy-1 GPI rnembrane (see Scheme 1) [19]. The tetrabenzoyl mannosyl bromide 30 was converted into orthoester 31a [15]. One portion was silylated [20] and then benzylated to give 31b, which upon treatment with bromine led to the glycosyl bromide 32. The remainder of 31a was completely benzylated, and one portion of the resulting material, 31c, was processed to give the acceptor 33a whereas the other was brominated to give glycosyl bromide 35. Coupling of 32 and 33b, led to 34a and debenzoylation to acceptor 34b which reacted with 35 to give trimannan 36 P11. Glycosyl bromides 32 and 35, being unstable, are best generated and used in situ. An approach to the same trimannan in which all reacting participants are stable is, however, outlined in Scheme 7b. The pathway takes advantage of some of the unique aspects of n-pentenyl glycosides. Thus, a major development in NPG chemistry emanated from mechanistic investigations which showed that intramolecular reaction of the cyclic halonium compound leading to the furanylium ion, --f
142
6 Glycosylation Methods: Use of n-Pentenyl Glycosides
v1
c
x 8 *
8
%
Scheme 7. Two routes to a trimannan from an n-pentenyl orthoester. (i) Pent-OH, 2,6-lutidine, CHzC12; (ii) tBuPh2SiCl; imidazole, THF; (iii) BnBr, NaH, B U ~ N ITHF; , (iv) 31b or c; Br2, CH2C12, 0 ° C ; (v) 31c CSA, CH2C12, 5OoC, 6 h; (vi) NaOMe; (vii) AgOTf, CHzCl,; (viii) TBAF, THF then Ac20, DMAP, CHzC12; (ix) Br2, Et4NBr, CH2C12; (x) NIS, Et&OTf, CH2Clz;(xi) NH3, MeOH; (ClAc)20, Et3N, CH2CI2; (xii) Zn, BQNI, EtOH then (ClAc)20.
U
144
6 Glycosylation Methods: Use of n-Pentenyl Glycosides
(Scheme 2, 6-+3), could be offset by the bimolecular process leading to 9, in the presence of excess nucleophile. For example, added bromide ion led to a vicinal dibromide; because, however, reductive elimination readily restored the double bond, dibromides 7 and 8 represent ‘sidetracked’ forms of an NPG. Nevertheless, the sidetracked material enables an hydroxyl group to be liberated, thereby creating a glycosyl acceptor 8 capable of reacting with a donor to give 7. The utility of the ‘sidetracked’ capability is illustrated in Scheme 7b. A portion of NPG 33a was debenzoylated to 33b and then ‘sidetracked’ to give acceptor 38. Coupling with orthoester 37 then gave dimannan 39a, which underwent routine protecting-group alterations to produce disaccharide acceptor 39b. Coupling with the remainder of 33a now produced 40. The major process for obtaining the previously described 36 now involved reductive debromination to regenerate the pentenyl moiety [22].
6.5 n-Pentenyl Orthoesters as Latent C2 Esters It is apparent from Scheme 7 that proton- or electrophile-driven reaction leads to specifically C2-0-acylated products. C2-Esters are important for controlling stereoselectivity in anomeric replacement reactions [ 1 11, and so the use of orthoesters as specific latent C2-esters has been explored in the context of a protected form of the ‘linkage region’ of proteoglycans, which contains four 1,2-trans diequatorial linkages (Scheme 8). For the C2-acylated galactoside acceptor, a simple route begins with galactosyl bromide 41 (Scheme 8a). Orthoester formation required the use excess pentenyl alcohol and tetrabutylammonium iodide as promoter to obtain 42a and thence 42b. Acid-catalyzed reaction of the latter in the presence of excess pentenyl alcohol, then benzylidination gave acceptor 43a. The xylosyl acceptor 46b (Scheme 8b) was obtained similarly from bromide 44 via the n-pentenyl orthoester 45. Diol 46a was subjected to selective silylation at C4, paving the way to 46b. It was expected that the uronate moiety would be problematic because such 2-0acyl donors usually lead preponderantly to orthoester products. Of several donors that were tested, trichloroacetimidates were found to give the least amount of orthoesters. Donor 49 was therefore prepared from commercially available benzyl P-glucoside, 47a, via methyl ester 48 as summarized in Scheme 8c. Coupling with galactoside 43a gave the disaccharide donor 50 as the major product, the orthoester (51) being minimized at 25%. The disaccharide acceptor 52b was obtained by coupling the ‘sidetracked’ xyloside 46b to the n-pentenyl galactoside 43b, followed by dechloroacetylation. The latter reaction was problematic and required use of the van Boeckel procedure [23]. The two disaccharides were then coupled to give 53a. Iodide-induced debromination [24], a milder alternative to the zinc reduction used for 42 -+ 38 in Scheme 7, afforded 54b. Finally, coupling with the protected serine 54 [25] occurred smoothly to give the desired ‘linkage region’ construct 55 [26].
6.5 n-Pentenyl Orthoesters as Latent C2 Esters
145
146
6 Glycosylution Methods: Use of n-Pentenyl Glycosides
6.6 Protecting Groups The presence of one free amine and four amide functions in the Thy-1 anchor (Scheme 1) sensitized us to the need for new, easily removable amine protecting groups. The n-pentenyl based protecting groups for alcohols and vicinal diols shown in Scheme 9a-c are outgrowths of NPG chemistry [27], all of which are cleaved or installed with halogen electrophiles. Notably, the acetalating agents in Scheme 9d can be put in place without disturbing acid-sensitive groups already present [28]. Glycosyl n-pentenoyl esters (Scheme 9e) have been found to be good glycosyl donors, a circumstance that provides evidence for ready loss of the pentenoyl group [29]. In the light of these precedents, amine protection via n-pentenoylation was examined. As shown in Scheme 9f installation for primary and secondary amines is routine, and cleavage occurs readily with iodine. C2-N-acylated sugars are, however, prone to give oxazolines as shown in Scheme 9g. Lemieux showed that this problem could be obviated by employing phthaloyl protecting groups [30], de-Nphthaloylation being effected by prolonged treatment with hydrazine or ethylenediamine. It has been shown [31, 321 that electron-withdrawing groups on the aromatic ring facilitate cleavage remarkably, as indicated by the difference for X = C1 and X = H in Scheme 9h. Cleavage of pentenoyl or tetrachlorophthaloyl (TCP) groups is therefore seen to occur very readily, and the very different procedures employed enable these protecting groups to be used orthogonally. This aspect was explored in the context of lipid A, 56 [33] (Scheme lo), a molecule in which all sites on the disaccharide need to be differentiated. The glucosaminide functions would be protected by either npentenoyl or TCP; but use of the former on the acceptor rather than the donor was dictated by the oxazoline problem noted in Scheme 9g. In the event Koenigs-Knorr coupling of 57 or 58 produced 59 in good yield. Comparison with lipid A, 56, shows that differentiation between the three acetylated sites of 54 would be necessary for a more useful precursor. Deacetylation with base would not be tolerated by the TCP group; but acid-catalyzed deacetylation was successful and benzylidination led to the more attractive counterpart 60 with the five critical sites being differentially accessible. With respect to the protected amines, treatment with ethylenediamine liberated one and iodine the other, giving 61 and 62 respectively [34]. Notably, cleavage of the benzylidine group with sodium cyanoborohydride [35] is tolerated by TCP [36].
6.7 Solid-Phase Iterative Couple-Deprotect-Couple Strategy Scheme 2 shows that NPGs have the potential to function as glycosyl donors and also as glycosyl acceptors via sidetracked intermediates (e.g. 8). The latter property
6.7 Solid-Phase Iterative Couple-Deprotect-Couple Strategy
h I
QfB I
1 (0 0
+ I '
8
q)==J 0
I
\
141
148
6 Glycosylation Methods: Use of n-Pentenyl Glycosides
Lipid A /OAC
AcO AcO BzO
Ad3
BzO
Oknt
-
57
DIFFERENTIALLY ACCESSIBLE SITES
Scheme 10. Orthogonal protecting groups for a lipid a precursor. (i) AgOTf; (ii) Me2CO/H20/HCl, 60"C, 20 h; PhCH(OMe)2/PF'TS/dioxane, reflux; (iii) ethylenediarnine, 60°C 2 h; (iv) 12 (2 equiv.), HzO/THF, 8 min.
was instrumental in a process used to assemble the high-mannose nonamannan component via an iterative deprotect-couple-deprotect strategy [37]. A solid-phase version of this procedure would have the advantage of minimizing transformations on the bound saccharide(s). An attempt to develop such an iterative strategy, shown in Scheme 11, used the known [38], bound pentenyl alcohol 63 for a KoenigsKnorr reaction with 64, by following the procedure developed by Frechet and Schuerch [39]. To test the viability of the cleavage reaction, compound 65 was treated with benzyl alcohol and NIS/TESOTf in wet dichloromethane to afford the
R=Bn
b)
OPent
+
BnO
ii
70
BnO
BnO
65
BnO
66
BnO
71
BnO
67
Scheme 11. A solid-phase version of NPG. (i) THF; (ii) pyridine, CH2C12; (iii) BnOH, NIS, TESOTf, wet CH2C12, 2 h; (iv) NaOMe/MeOH/THF; Br2, Et4nBr, CH2C12; (v) NIS, TESOTf, CHzC12, 2 h; (vi) 0.1 M SmI2, THF, 30 mix; (vii) thiourea, methoxyethanol, 8 0 T , 6 h.
68 R=Ac
a)
Bn?% BnO
63
OH
u
P
150
6 Glycosylation Methods: Use of n-Pentenyl Glycosides
benzyl glycoside 66 in 60% yield and, presumably, the bound iodomethyltetrahydrofuran 67. For a more elaborate test case, the sidetracked acceptor 69 was prepared and coupling with 68a proceeded smoothly to give a dibromide. Zinc could not be used to restore the double bond, because of the solid-solid interaction that would be involved. A one-electron reductive elimination with samarium I1 iodide [24] proceeded smoothly, however, to give 70. Unfortunately, efforts to cleave the disaccharide from the solid support to produce 71 were unsuccessful. FTIR data suggested that addition to the double bond overwhelmed the cyclization reaction. The above results meant that the oxidative cleavage worked sometimes (65-+ 66), but not always (70 -+ 71). The use of sidetracked acceptors such as 69 might, therefore, be unreliable. Nevertheless, use of NPG as donors was still an option and so the oxidative cleavage aspect was replaced by a photocleavable alternative (Scheme 12). Thus, the Rich-Guwara linker 72A [40]was investigated. Success was had with a linear trimannan, and so a branched trimannan was tested, because this would be more demanding in that chemoselectivity deprotection would be required. This study is reported in Scheme 12. The Rich-Guwara photolinker was successfully coupled with diester 73, and chemoselective deacylation of the bound monosaccharide, 74a +74b, was found to proceed smoothly. Although coupling with donor 68b gave 15a in only moderate yields, ranging from 58-76'3'0, subsequent deprotection of the C6 acetate and iterative coupling with donor 68b proceeded without incident to give the resin-bound trisaccharide 76. Irradiation of the A-series trisaccharide required three days for recovery of optimum (10%) amounts of trisaccharide 77. On the assumption that this low yield was because of problems with the photocleavage reaction, a new linker, 72B, was designed. Advantages over 72A were (a) that linkage to the sugar was through a secondary, rather than primary, hydroxyl, and (b) that the electron-withdrawing amide carbonyl was remote from, rather than attached to, the benzene ring, where its deactivating effect would be irrelevant to the photocleavage event [41]. Indeed with 76B, the cleavage was very much faster and the overall yield of 77 was very much better [41]. An effort has also been made to synthesize polymer bound, fully deprotected saccharides by the couple-deprotect-couple iterative strategy [42]. A crucial problem with this approach was, however, that normally used benzyl groups, as in Scheme 12, would be problematic, because hydrogenolytic cleavage would involve a solid-solid interaction. Dissolving metal options were examined, but were also problematic in that the resin backbone apparently acted as an electron sink. Ester protecting groups were the only other option, and so concerns about their deactivating affect on the NPG donors were dispelled by success with preliminary experiments. The plan in Scheme 13 was therefore tested. The known NPG 78 [43] was converted into the differentially protected counterpart 79, and coupling with the polystyrene resin, A, led to 80a which reacted with 81 to give disaccharide 82a. Another decouple-couple iteration led to trisaccharide 83. Global deprotection by treatment with ethylenediamine in methoxyethanol at 70 "C for 4 h gave the fully deprotected bound trisaccharide 84.
6.7 Solid-Phase Iterative Couple-Deprotect-Couple Strategy
wI . -
P OD
\ .-
'-
I
+
Q
t
15 1
152
6 Glycosylution Methods: Use of n-Pentenyl Glycosides
..-
.-.-
;.i d
4 >
P
d 0 \
?
References
153
The sequence could be repeated with the tentage1 macrobeads, B, and the grafted crown linkers, C. The last was particularly valuable in that acetylation followed by photocleavage afforded 85, the identity of which was verified by independent synthesis [42].
References 1. For a concise review see: A. J. Bridges in Chem Tracts-Organic Chemistry, 1996, 9, 215-223. 2. B. Fraser-Reid, U. E. Udodong, Z. Wu, H. Ottosson, R. Merritt, C. S. Rao, C. Roberts and R. Madsen. Synlett, 1992, 927-942. 3. D. R. Mootoo, P. Konradsson, U. Udodong and B. Fraser-Reid. J. Am. Chem. SOC.,1988, 110, 5583-5584. 4. G. J. Boons, Tetrahedron, 1996, 52, 1095-1121. 5. M. L. Sinnott. Advances in Physical Organic Chemistry. 1988, 24, 113-204. 6. P. Deslongchamps. Stereoelectronic Efsects in Organic Chemistry. Pergamon, Oxford. 1983. 7. A. J. Ratcliffe, D. R. Mootoo, C. W. Andrews and B. Fraser-Reid. J. Am. Chem. Soc., 1989, I l l , 7661-7662. 8. C. W. Andrews, J. P. Bowen and B. Fraser-Reid. J. Chem. SOC. Chem. Comm., 1989, 19131916. 9. B. Fraser-Reid, Z. Wu, C. W. Andrews, E. Skowronski and J. P. Bowen. J. Am. Chem. Soc., 1991, 113, 1434-1435. 10. B. G. Wilson and B. Fraser-Reid. J. Org. Chem, 1995, 60, 317-320. 11. H . L. Frush and H. S. Isbell, J. Res. Nutl. Bur. Stds, 1941, 27, 413. 12. S. Oscarson and U. Tedebark. J. Carbohydr. Chem., 1996, 15, 507-512. 13. G. J. Boons, Contemp. Org. Syn., 1996, 3, 173-200. 14. J. F. King and A. D. Allbutt. Can. J. Chem., 1970, 48, 175441767, 15. R. U. Lemieux and N. J. Chu. Abstracts of Papers. Am. Chem. SOC., 1958,133, 31N. 16. A. F. Bochkov and G. E. Zaikov. Chemistry of the 0-Glycosidic Bond, Chapter 2, Pergamon Press, Oxford, 1979. 17. For some recent examples see: W. Wang and F. Kong. J. Org. Chem. 1998, 63, 5744-5745. L. Snaidman, C. Johnson, C. Crasto and S. M. Hecht. J. Org. Chem., 1995,560,3942-3943. 18. S. Hanessian and J. Banoub. Carbohydr. Res. 1977, 53 C13-Cl6. 19. A. S. Campbell and B. Fraser-Reid. J. Am. Chem. SOC.,1995,117, 10387-10388. 20. S. Hannesian and P. Lavallee, Can. J. Chem. 1975, 53,2975-2978 21. C. Roberts, C. L. May, and B. Fraser-Reid. Carbohydr. Lett., 1994, 1, 89-93. 22. C. Roberts, R. Madsen and B. Fraser-Reid. J. Am. Chem. Soc., 1995,117, 1546-1553. 23. C. A. A. van Boeckel and T. Beetz. Tetrahedron Lett. 1983,24, 3775. 24. J. R. Merritt, J. S. Debenham and B. Fraser-Reid. J. Carbohydr. Chem., 1996, 15, 65-72. 25. M. Meldal and K. J. Jensen. J. Chem. SOC.,Chem. Commun., 1990,483-484. U. K. Saha and R. R. Schmidt. J. Chem. Soc., Perkin I, 1997, 1855-1858. 26. J. G. Allen and Bert Fraser-Reid. J. Am. Chem. Soc., 1999, 121, 468-469. 27. Z. Wu, D. R. Mootoo and B. Fraser-Reid. Tetrahedron Lett., 1988, 29, 6549. 28. R. Madsen and B. Fraser-Reid. J. Chem. SOC.,Chem. Commun., 1994, 749-750. R. Madsen and B. Fraser-Reid. J. Org. Chem., 1995, 60, 772-779. 29. J. C. Lopez and B. Fraser-Reid. J. Chem. SOC.Chem. Comm., 1991, 159-161. 30. R. Lemieux, T. Takeda, B. Chung. Synthetic Methods for Carbohydrates (Ed. H. S. El Khadem, ACS Symposium Series, Washington, D. C., 1976, vol. 39, pp. 90-115. 31. J. S. Debenham, R. Madsen, C. Roberts, B. Fraser-Reid. J. Am. Chem. Soc., 1995,117, 33023303. 32. J. C. Castro-Palomino, R. R. Schmidt, Tetrahedron Lett. 1995, 36, 5343-5346. H. Shimizu, Y . Ito, Y. Matsuzaki, H. Iijima, and T. Ogawa. Biosci. Biotech. Biochem, 1996, 60, 73-76. 33. C. R. H. Raetz. J. Bacteriology, 1993, 175, 5745-5753. 34. S. L. Griffiths, R. Madsen, and B. Fraser-Reid. J. Org. Chem., 1997, 62, 365443658,
154
6 Glycosylation Methods: Use of n-Pentenyl Glycosides
35. P. T. Garegg. Pure Appl. Chem., 1984, 56, 845-858. 36. J. S. Debenham, S. D. Debenham, and B. Fraser-Reid. Bioorg. Med. Chem., 1996, 4, 19091918. 37. J. R. Merritt, E. Naisang and B. Fraser-Reid. J. Org. Chem., 1994,59, 4443-4449. 38. M. Bernard and W. T . Ford. J. Org. Chem., 1983, 48, 326-332. 39. J. M. Frechet and C. Schuerch. J. Am. Chem. Soc., 1972, 94,604-609. 40. D. H. Rich and S. K. Guwara. Tetrahedron Left., 1975, 16, 301-304. 41. R. Rodebaugh, B. Fraser-Reid and H. M. Geysen. Tetrahedron Lett., 1997,38,7653-7656. 42. R. Rodebaugh, S. Joshi, B. Fraser-Reid and H. M. Geysen. J. Org. Chem., 1997, 62, 56605661. 43. J. S. Debenham, R. Rodebaugh and Bert Fraser-Reid. Liebigs AnnJRecueil, 1997, 796-802.
Carbohydrates in Chemistry and Biology Beat Ernst, Gerald W. Hart, Pierre Sinay copyrightQ WILEY-VCH Verlag GmbH, 2000
7 Glycosylidene Diazirines Andrea Vasella, Bruno Bernet, Martin Weber, and Wolfgang Wenger
7.1 Introduction Glycosylidene diazirines are useful as precursors of glycosylidene carbenes [I]. These cyclic, amphiphilic singlet alkoxycarbenes enable the formation of two bonds at the anomeric center. Although many aspects of the chemistry of pyranosylidene diazirines have been reviewed [2-51, furanosylidene diazirines [ 61 are hardly known because of their high reactivity and concomitant poor stability. Furanosylidene carbenes or carbenoids have been generated from the readily available lactone sulfonyl hydrazones [7].Whereas diazirines generate carbenes either thermally or photochemically under mild conditions, and simultaneously only produce dinitrogen, sulfonyl hydrazones, however, also generate potentially reactive side-products [7, 81. Glycosylidene carbenes, like other intermediates, are reactive and versatile. Their precursors-glycosylidene diazirines (= 1-azi-l,5-anhydroglycitols)-are thus expected to be useful. They have been devised primarily to serve as universal, highly reactive glycosylating reagents responding to the kinetic acidity of glycosyl acceptors, irrespective of their nucleophilic properties and of steric hindrance, and requiring no promoter. Their advantages will be discussed, as will their two disadvantages, uiz. their restricted stability, and their preparation which requires five (generally high-yielding) steps from hemiacetals.
7.2 Synthesis of Glycosylidene Diazirines The original route, depicted in Scheme 1, for the synthesis of the benzylated glucosylidene diazirine 7 [6, 91, is still used with minor variations, as evidenced by the preparation of the GlcNAc-derived analog 14 [3]. Details have been published, and some comments will prove useful.
156
7 Glycosylidene Diuzirines
BnO% BnO
i_ 1
B BnOn
B BnO n O
6 OBn N O
B BnO .
H
0
6 NHOH
BnO OH
O
h
2
%,
y
v
BnO BnO
BnO
Brio
7
iv
BnO& BnO BnO
NH
6
vi
BnO% BnO AcHN
NH
B BnO n 0
6
iii
N
O
H
AcHN
OH
8
/OR
E45 RR==MHs
B BnOn
~
N
O
6NHOH
AcHN
10
9
vii
c xF*n:niE
BnO% BnO y
ix
AcHN
AcHN
14
13
NH
&: ;B AcHN
/OR N
Scheme 1. Reagents: (i) Na, 96% EtOH, then NH3OH C1 and 1 , 7 h at 60°C, quant. (variable ratio of 2/3, ( E / Z )cu 65:35); (ii) NaOAc, NaI04, EtOH/H20, 19 h at 70°C, 79% from 1; (iii) pyridine, MsCl, CH2C12, 12 h at 0 ---t room temp., 87%; (iv) sat. NH3 in MeOH, CH2C12, 5 days at room temp., 76%; (v) MqN, 12, CH2C12, 2-5 h at -5O"C, 83%; (vi) Na, MeOH, then NH30HCl and 8, 33 h at 60"C, quant. (variable ratio of 9/10); (vii) NaOAc, NaI04, EtOH/H20, 18 h at 50°C, 70% from 8; (viii) Et3N, TsCl, CHzC12, 3 h at O T , 100%; (ix) sat. NH3 in MeOH, MeOH, 7 days at -2O"C, ca 70%; (x) Et3N, 12, CH2C12/MeOH, 3 h at O T , 68% from 12.
Formation of the oximes-generally obtained as ( E / Z )isomers and, most clearly [ 10, 111 (see also Ref. [ 121) and 2-acetamidofor 2,3,4,6-tetra-0-benzyl-~-glucose 3,4,6-tri-O-benzyl-2-deoxy-~-glucose oximes [3], as a mixture with the cyclic p-Dpyranosyl hydroxylamines (3 and 10, respectively)-proceeds readily at a pH of ca 6. Yields are high. The best procedure for the oxidation to the hydroximolactones depends on the structure of the oximes. Several oxidants have been tested. MnOz is generally reliable when prepared according to Attenburrow [ 131; commercial Mn02 has led to low yields [ 141.Oxidation is slightly exothermic. Fresh batches of MnOz might have to be added during the oxidation of large batches. Starting material and product have very similar RF values, but stain differently (H2S04, mostain) on the TLC
7.2 Synthesis of Glycosylidene Diazirines
157
plate. If the structure of the starting material enables formation of 1,4- and 1,5hydroximolactones, both might be formed [ 141. The relative amounts occasionally depend upon the oxidant (e.g. Hg(OAc)2 us 02/CuC12 in pyridine). NCS in the presence of DBU at low temperatures (ca -40°C) is a faster oxidant than MnO2. Low temperature is required for the oxidation of 0-acetyl oximes to avoid migration of the acetyl group from OC(4) to OC(5) [15]. Occasionally, NaI04/NaOAc has proven useful. 0-Sulfonylation of the hydroximolactones is unproblematic. Sulfonyl chlorides or anhydrides in the presence of base react rapidly at low temperature. The products often crystallize readily. A range of sulfonates has been tested [3]. Mesylates are often well suited; triflates are sometimes too unstable, although Beckmann rearrangement does not readily occur [ 141. Formation of the diaziridine requires a protic solvent; MeOH has been used as a standard. The concentration of NH3 required for the transformation depends on the nature of the sulfonyl group and on the acceptor properties of the 0-protecting groups. For the transformation of benzyl-protected sulfonates, MeOH must be saturated with NH3 at 0 "C in a thick-walled flask (the volume increases by ca 30% and the solution contains ca 24.5 g NH3 in 100 mL MeOH; it is stable for months at -20 "C); the reaction is performed at 22-26 "C, and the pressure is maintained by closing the flask with a septum; alternatively an autoclave may be used. The 2,3,4,60-pivaloylated glucose-derived hydroximomesylate reacts much faster [3]. The 2,3,4,6-0-acetylated glucose-derived hydroximotriflate reacted with half-saturated NH3/MeOH/CH*C12 at -20 "C without deacetylation [ 151. The diaziridines are ninhydrin-positive, stain dark blue with mostain, and oxidize KI to 12 in the presence of acid. They often crystallize from EtzO, and their purification by crystallization leads to improved overall yields. They are acid-labile; chromatography on silica gel must be rapid. It has led to slight losses even in the presence of base (Et3N); acetone is often a suitable (co)solvent. Crystalline diaziridines can be kept for months at -2O"C, and their solutions are stable in the absence of acid and oxygen. At 25°C and in the air, the diazirines turn red, presumably by forming increasing amounts of tetrazines. The diaziridines are usually obtained as mixtures of the two trans diastereoisomers, readily equilibrating in the presence of traces of acids. The ratio of the isomers depends on the glycosylidene residues. Oxidation of the diaziridines to diazirines requires some skill; anhydrous conditions are mandatory. Oxidation with I2 in the presence of a tertiary amine is the standard procedure. It was originally performed in MeOH and in the presence of 1-azi-glucose 7 crysEt3N. Under these conditions, the 2,3,4,6-tetra-O-benzylated tallizes from solution and can be isolated by filtration under anhydrous conditions [9]. For some diazirines, however, it is advantageous to perform the oxidation in CH2C12, using I2 and Me3N. The reaction corresponds to a titration, it is stopped when the solution remains slightly yellow. Because excess 12 is not readily removed, it is best to add a small amount of the starting diaziridine to discharge the color of the solution. The product is purified by filtration through a short Si02 column and thoroughly dried under high vacuum; a low boiling solvent (CH2C12) is recommended. On TLC, the diazirines stain purple with a solution of 4-(4-nitro-
158
7 Glycosylidene Diazirines
benzy1)pyridine; this is a specific and useful way of detection. Acyl-protected diazirines are more stable than their benzylated analogs and can be purified by flash chromatography at 0°C; solvents should be low boiling. The fractions are cooled, and condensation of water must be avoided [3, 151. The diazirines remain in the crystalline form or in solution for several weeks at -78 "C; 0-acyl protected diazirines can be stored at -20 "C.
7.3 Stability of the Glycosylidene Diazirines The stability of l-azi-l,5-anhydrohexitols depends on the substituents (protecting groups), the configuration, and the conformational flexibility. It has been quantified by thermolysis of the glycosylidene diazirines in methanol at 298 K [3, 15, 161; the results are given in Table 1. Their relative stability has been rationalized by postulating sequential (non-synchronous) heterolytic breakage of the C (1),N bond, leading to a cationic intermediate and requiring a conformational change of the pyranose ring whereby the pseudoequatorial C-N bond becomes pseudoaxial. Hence, acceptor substituents should increase the stability, and so should conformational locking, as by an intramolecular NH. . .OC(1) hydrogen-bond in the N-acetylallose derivative 25.
7.4 Glycosidation by Glycosylidene Diazirines 7.4.1 General Aspects Deprotonation of the glycosyl acceptor by a glycosylidene carbene ought to lead to a highly reactive, initially unsolvated ion pair, where both donor and acceptor are activated and should react readily with each other. Stereoelectronic effects dictate that deprotonation of the acceptor occurs in the a-plane of the carbene (more or less equivalent to the plane of the pyranoside ring), whereas addition of the oxyanion to the oxycarbenium cation has to occur in the mplane, i.e. more or less perpendicular to the a-plane, and preferentially from the axial direction (illustrated in Scheme 2 by the carbene derived from the benzylated glum-diazirine 7). Glycosidation by diazirines has been studied by using equivalent amounts of glycosyl acceptor and donor. It is expected that yields of the products increase with excess diazirine; occasionally this was shown to be so. Solvents have not systematically been optimized, but toluene, THF, and dioxane seem well suited; early experiments were mostly performed in dichloromethane. The course of the glycosidation of hydroxy compounds by glycosylidene diazirines is mainly dictated by four factors:
159
7.4 Glycosidution by Glycosylidene Diazirines Table 1. Kinetic parameters for the thermolysis of 1-aziglycosesin MeOH.
Diazirine
Compound
logA
15 R = Piv 16 R = AC 17 R = 4-F-Bn
23.0 25.0 21.6 23.7
13.4 14.1 11.6 13.8
33 202 181 43
22.4 24.0 21.0 23.1
1.7 4.8 -7.5 2.7
18
22.2
12.4
110
21.7
-3.2
19 R = B n 20 R = A c
23.2 20.5
14.2 11.4
I 45
22.6 19.9
5.5 -8.2
20.0
11.4
23
19.5
-8.2
-3.1
7 R = Bn
N
MeophT%r
BnO
AH= AS= (298 K) (298 K) [kcal [cal mol-' mol-'1 K-'1
E, [kcal mol-'1
z
(298 K) [min]
N
r *FCR
N
*::kS+yr
ND"
ND"
23
ND"
ND"
24
ND"
ND"
l4
22.6
12.6
112
22.0
25
28.1
15.1
4159
27.2
26 R = B n
20.8 22.3
11.4 12.1
88 202
20.2 21.7
BnO N OPiv PivO
Bn$Ss-,,
N
AcHN N
8.1
N
//"
RO OR
Ro
N
27 R = A c
-8.4 -5.0
160
7 Glycosylidene Diuzirines
Table 1 (continued) Diazirine
Compound
B n O - ' BnO f $ O a , N OBn BnO BnO
logA
21.8
12.2
T
(298 K) [min]
79
BnO BnO
OH
AS= (298 K) [cal mol-I K-'1
21.2
-4.8
- 100°C.
&:]
BnO% BnO
AH= (298 K) [kcal mol-'1
28
"Not determined. bVery unstable; slow decomposition even at
BnO
E, [kcal mol-l]
-
BnO
p-D
1
11 (OBn
(OBn
7
I
1
/OBn
I
OBn
BnO BnO
30
BnO
Scheme 2. Glycosidation of alcohols by gl ycosylidene carbenes derived from diazirines.
7.4 Glycosidution by Glycosylidene Diazirines
161
1) The kinetic acidity of the hydroxy group (inversely proportional to its basicity and more or less proportional to its nucleophilic properties). A sufficiently high kinetic acidity ensures rapid protonation of the carbene. Even an oxyanion derived from a poorly nucleophilic alcohol reacts readily with the simultaneously generated oxycarbenium cation. This property constitutes a major advantage of glycosylidene diazirines in the glycosidation of acids [ 171, phenols [9], highly fluorinated alcohols [ 181, hydroperoxides 1191, and hydrated Ti02 [ 151. Slow protonation of the carbene by a hydroxy compound of low kinetic acidity will lead to increasing amounts of azines (30 in Scheme 2), resulting from the interaction of the carbene with the starting diazirine. The azines are formed as a mixture of diastereoisomersthat are converted, by mild acid catalysis, mostly to the ( Z / Z )isomer [3]. 2) Hydrogen-bonding (a) Hydrogen-bonding influences the kinetic acidity of hydroxy groups. H-bond acceptors (that are not simultaneously hydrogen-bond donors) have enhanced kinetic acidity, whereas H-bond donors have reduced kinetic acidity; intramolecular hydrogen-bonding might thus determine the regioselectivity of deprotonation by the glycosylidene carbene-one of the conditions to be fulfilled for regioselective glycosidation. This effect has led to the regioselective glycosidation of dihydroxybenzene derivatives, where one of the phenolic OH groups functions as an intramolecular H-bond donor to a carbonyl group and is thereby glycosylated more slowly (Figure la) [9]. (b) Intra- or intermolecular hydrogen-bonding can also influence or determine the regio- and stereoselectivity of the ion pair combination resulting from deprotonation of the glycosyl acceptor. Whereas the kinetically most acidic OH group is deprotonated in the o-plane, a second OH group, hydrogen-bonded to the deprotonated OH group (and now linked by a H-bond to the newly generated oxyanionic center, Scheme 2) might be located in or close to the n-plane and attack the intermediate oxycarbenium ion. This effect has been demonstrated for a range of diols [20-251 and triols [26-291. It has also been evidenced for N-acetylglucosamine-deriveddiazirines, for which hydrogen-bonding to the NH group lead to the predominant formation of a-D-glycosides of sufficiently strong hydrogen-bond-accepting alcohols [301. 3) Solvation of the intermediate oxycarbenium ion. Solvation of the initially unsolvated or at least not optimally solvated oxycarbenium ion might involve the solvent, the glycosyl acceptor, or the C(2) substituent of the carbenium ion [18]. In an inert solvent, such as dichloromethane, solvation will occur by the (nucleophilic) glycosyl acceptor (inter- or intramolecularly) if it is sufficiently nucleophilic, or by the C(2)O-benzyl group for the less nucleophilic glycosyl acceptors such as phenols (as evidenced by studying the 2-deoxy analog 24 [31]). THF seems to solvate the carbenium ion well, and preferentially from the axial direction, leading preponderantly to equatorial glycosides. 4) In contradistinction to other methods of glycosidation, steric hindrance does not seem to be an important factor, as long as the hydroxy group is sufficiently acidic [ 18, 291. The following transformations illustrate these points.
162
A
7 Glycosylidene Diazirines
a)
b)
C)
F
3
C
Y
OGlcBn.,
/ OGlcBn, toluene: 79%, 8915
,,11..'
'...,,,
OGlcBn( toluene: 79%. 8416
CHzCI2: 34% (hv: 55%), 5050
dioxane, 25 "C: 76%. 95: 5 DME,25 "C 80%. 98: 2 EtCN, 25 "C: 5446,9010(16% of 31) EtCN, hv, -60 "C: 25%. 8713 (55% of 31)
31
e) CF3(CF2)5CH2CH~-OGlcBn, dioxane, 25 "C: 68%. 76:24
CHF~(CFZ)&H~~GICBQ toluene: 73% 6733
dioxane: 90%. 1:l mixture of p-D-isomers only
dioxane, 25 "C: 79%,78:22
CICH2CH2CI: 62%. 65:35 (4% of regioisorner, 4555)
Figure 1. Products of the reactions of the diazirine 7 with mono- and dihydroxy compounds: solvents, total yields, and p-D/a-D ratios (GlcBm = 2,3,4,6-tetra-0-benzyl-~-glucopyranosyl).
7.4.2 Glycosidation of Strongly Acidic Hydroxy Compounds Glycosidation of Phenols Glycosidation by the 1-azi-tetra-0-benzylglucopyranose7 proceeds in yields of approximately 75-80%, and leads mostly to the P-D-anomers [9]; presumably, the use of THF will increase the anomeric selectivity (Figure la, b). The analogous I -azimannose 19 yielded mostly a-D-mannosides, but has not been thoroughly studied [9].
7.4 Glycosidation by Glycosylidene Diazirines
163
The influence of intramolecular hydrogen-bonding is evident from the regioselective monoglycosidation of methyl orsellinate (Figure 1a) [9]. Upon addition of a second equivalent of diazirine, the chelated OH group is also glycosylated (67%,),although with less anomeric selectivity, as also observed for 4-nitrophenol. The insensitivity to steric hindrance is seen from the result of glycosylating 2,6-di(tert-butyl)-4-methylphenol(Figure 1b) [9]. Thiophenols react similarly to phenols; 4-methoxythiophenol yielding 70% of a D of thioglucosides [32]. 43 : 57 C X - D / ~ - mixture Glycosidation of Fluorinated Alcohols The influence of pK and the insensitivity to steric hindrance is seen from the glycosylation of fluorinated alcohols (Figure lc) [ 181. Glycosidation of trifluoroethanol, hexafluoro-2-propanol, and hexafluoro-tert-butanol by one equivalent of the diazirine 7 in dioxane yielded the anomeric glycosides in yields of 70-74% and in ~-D/.-D ratios ranging from 77:32 to 95:5. The solvent has an influence on the anomeric ratio, which changes for hexafluoro-tert-butanol from ~ - D / C X -= D 84 : 16 (75%) in dichloromethane to 98:2 (80%) in DME. The formation, upon glycosidation in propionitrile at -60°C, of the imino ether 31 (55%) besides the glycosides evidences the formation of an oxycarbenium cation, its solvation, and the preferred axial attack of the solvent. 3,3,4,4,5,5,6,6,7,7,8,8,-tridecafluorooctanoland of Glycosidation of CHF2(CF2)&H*OH by 7 in dioxane proceeded similarly and yielded 68 and 79% of the glucosides (P-D~CX-D = 76: 24 and 78 :22).
7.4.3 Glycosylation of Weakly Acidic Hydroxy Compounds Glycosidation of Monovalent Alcohols In contradistinction to the glycosylation of hexafluoro-tert-butanol, tert-butanol is glycosylated in only 34% yield under similar conditions (Figure 1d). Glycosylation at low temperature (photolytic generation of the carbene) doubled the yield, but had no influence on diastereoselectivity (IX-D/~-Dca 1 : 1). This dependence on the mode of generating the carbene is not general, and might reflect the temperaturedependence of the association of tert-butanol. Monoalcohols with o-acceptor substituents (such as partially protected monosaccharides) are expected to be more highly acidic and, hence, be glycosylated in higher yields. Indeed, 1,2: 5,6-di-0isopropylidene-a-D-glucofuranose yielded 75% of a 2 : 3 mixture of the corresponding anomeric disaccharides (Figure 1e) [ 181. The influence of acidity is also seen in the successful glycosidation of (hydrated) Ti02 [15]. The OH groups of hydrated Ti02 are characterized by pK values of 3.8 and 6.6. Exposure of Ti02 to benzylated or acetylated azi-glucoses 7 and 16 led to formation of a monomolecular layer of strongly (presumably covalently) bonded glucosyl residues (density 1.5 0.9 glucosyl moieties nm-2). The acetylated glucosyl moieties were deacetylated without removing the glucosyl moiety.
164
7 Glycosylidene Diazirines
Glycosidation of Diols and Triols Efsects of hydrogen-bonding The enhancing influence of an (intramolecular) hydrogen-bond on the kinetic acidity of the H-bond-accepting hydroxy group is seen from the (concentration independent!) result of the glycosidation of the myo-inositol-derived orthoester (Figure I f ) [26]. The two diastereoisomers derived from monoglycosylation of one each of the two enantiotopic hydrogen-bonded OH groups were obtained regio- and diastereoselectively in high yields. The low reactivity of the isolated equatorial OH group is because of a (bifurcated) hydrogen-bond. This effect also operates in the regioselective glycosidation at OC(2) of methyl 4,6-O-benzylidene-a-~-altropyranoside, yielding 62% of a 2: 1 mixture of anomers in dichloroethane (Figure lg) [20]. As expected, the intramolecular hydrogen-bond reduces the kinetic acidity of HOC(3), but enhances its nucleophilicity and leads to glycosylation at OC(3) bromide under Lemieux halogenwith 2,3,4,6-tetra-O-benzyl-a-~-glucopyranosyl exchange conditions, resulting in 68% of the a-D-configured, 1,3-1inked disaccharide (and 10% of the anomeric regioisomers). Combined efsects of intramolecular hydrogen-bonding and of stereoelectronic control The intramolecular hydrogen-bond between HOC(3) and the anomeric methoxy group in methyl 4,6-0-benzylidene-a-~-allopyranoside is expected to lead to protonation of the carbene mostly by the kinetically more highly acidic HOC(2) (Figure 2a) [22]. This is presumably taking place. In contradistinction to the altro-diol, however, the two OH groups are cis-oriented. Stereoelectroniccontrol requires that protonation occurs in the o-plane of the carbene and attack of the nucleophile on the ensuing oxycarbenium cation proceeds in the n-plane. HOC(3) is much closer to the x-plane than -0C(2). Glycosylation in toluene at 70 "C or in dioxane at 24 "C indeed leads mostly to the a-D-anomer of the 1,3-linked disaccharide [22]. The predominant a-D-configuration reflects the stereoelectronic control. Replacing these solvents by the more nucleophilic THF at -85°C leads to participation of the solvent. THF competes with
toluene: 79%.
C(2)0/C(3)0 2080 (68:32and 28:72)
CH2C12,-85", hv: 81%, C(2)0/C(3)O/C4)05:81:14(60:40,23:77, and 3664)
THF, -85", hv: 79%, C(2)0/C(3)0 7228 (9010and 3367)
Figure 2. Glucosylation of (a) methyl 4,6-O-benzylidene-a-~-allopyranoside and (b) benzyl ribopyranoside by the diazirine 7:solvents, total yields. regioselectivity, and p-D/a-Dratios.
p-D-
7.4 Glycosidution by Glycosylidene Diuzirines
165
Scheme 3. Preferred formation of the 3-O-P-~-glucosylateddimer in the reaction of 7 with benzyl (3-D-ribopyranoside.
HOC(3) in attacking the intermediate oxycarbenium ion, again from the axial di~ of the 1,2-1inked disaccharide! rection, and the main product is now the p - anomer Similarly for benzyl P-D-ribopyranoside, preferential protonation of the carbene ought to occur by either HOC(2) or HOC(4), but HOC(3) is in a better position to attack the carbenium ion from an axial direction. The main product, isolated in 65% yield, is the a-Danomer of the 1,3-linked disaccharide (Figure 2b) [28]. The rationalization of that reaction is illustrated in Scheme 3. In THF at -78 "C, however, the main products are the p-D anomers of the 1,2- and 1,4-linked disaccharides. More examples of regioselective glycosidations resulting from the combination of these factors have been published and a particularly striking effect of hydrogenbonding is provided by the glycosidation of the N-phthaloylated allosamine derivatives. The dominant product of the a-D-configured diol is the 1,3-linked disaccharide (Scheme 4a) [23]. The anomeric configuration suggests that the regioselectivity is the result of a protonation by HOC(4) and an interception of the carbenium ion by HOC(3); indeed, ' H NMR analysis showed the presence of a very strong hydrogen-bond between HOC(3) and the phthaloyl group, and a weaker hydrogen-bond between HOC(4) and HOC(3). The former hydrogen-bond strongly reduces the kinetic acidity of HOC(3), the latter orients the protonating HOC(4) close to OC(3). In agreement with this, the a-D-configured monoalcohol is unreactive (Scheme 4b), whereas its anomer is glycosylated (Scheme 4c), because the N-phthaloyl group now adopts a different conformation; also the anomeric diol is no longer regioselectively glycosylated (Scheme 4d). The results of the glycosylation of the a-D-configured trio1 (Scheme 4e) evidences that the weakest hydrogen-bond is that from HOC(4) to HOC(3)! Intramolecular solvation of the intermediate oxycarbenium ion has also been postulated to explain the high-yielding glycosylation of the tertiary hydroxy group
7 Glycosylidene Diazirines
166 a)
80%, 90:lO
no reaction
C)
*Thp
OAll Bn4Glc0
NFt
66%,2 1 3 9
4
CHIOBn H
o ~ HO
O
A
l
l
B n 4 G l f : N OAll + OH BqGlcO
29%.a 6 5
33%,39:61
B n 4 G l c ? !
HO FNOAll
HO FtNOAll 9%,(only p-D)
OAll NFt
+
E N Bn4Glc0 FtN OAll 51%. 72:28
Scheme 4. Glucosylation of anomeric N-phthaloylatedallosamine derivatives by one equivalent of the diazirine 7 in dioxane at room temperature: total yields and a-D/p-D ratios.
of 10-0-acetylginkgolide A by a lactose-derived diazirine (Scheme 5a) [29]; intramolecular participation of the carbonyl group of the adjacent lactone ring is presumably playing an important role also in the glycosylation of ginkgolide B, where reaction with 3.5 equivalents of 7 in THF yielded 42% of the all-P-D-configured trisaccharide (Scheme 5b) [29]. Thus, regioselective glycosidation of diols and triols by diazirines is feasible and often strikingly successful. Its course can be predicted, even if the factors are complex, if the hydrogen-bonds in the glycosyl acceptor are known. Analytically, the results of glycosylation provide important clues to the location of hydrogen-bonds (Figure 3a), e.g. evaluation of the influence of weak intramolecular OH. . .F-C hydrogen-bonding in apolar solvents (Figure 3b) [24, 251. There is yet another factor, operative in carbenes derived from 1-azi-2-acetamido-2-deoxy sugars that can occasionally be exploited. Efect of intermolecular hydrogen-bondingfrom the diazirine to the acceptor Surprisingly, thennolysis of the N-acetylglucosamine- and N-acetylallosamine-derived diazirines 14 and 25 in methanol led predominantly to the 1,2-cis-configured
7.4 Glycosidation by Glycosylidene Diuzirines
Me
167
28 (1.3 equiv.)
HO 3
THF, 25°C
0 92% of B-D-anomer
b'
0
N
Me
-
Me
7 (3.5 equiv.) THF, 25°C
42%
R = GlcBn, p+l p+3 p-10
15% p+l p-3 a+10 13% a+l p+3 p-10 24% diglucosides no rnonoglucosides
Scheme 5. (a) Lactosylation of 10-0-acetylginkgolide A by 28. (b) Glucosylation of ginkgolide B by 7.
a-r>-glycosides; similarly, glycosidation of 2-propanol (2 equivalents) by 14 at -84 "C yielded 70% of the a-D-glycoside (no 0-D-anomer observed) and 13% of the dihydrooxazole [30]. At 26 "C, the dihydrooxazole (resulting from protonation of the carbene by the acetamido group) became the major product. Under analogous conditions (-84 "C), hexafluoro-2-propanol yielded between 58 and 9 1% glycosides, depending on the excess of alcohol (1 to 10 equivalents), the anomeric ratio varying between 72 :28 and 80 :20. Glycosidation at 26 "C of 2 equivalents of hexafluoro-2propanol led to higher yields of glycosides (72 compared with 59%) and higher anomeric selectivity (.-D/~-D = 88 : 12). Glycosidation of the still more highly acidic
Figure 3. Intramolecular hydrogen-bonding in (a) ally1 2-deoxy-2-phthalimido-a-~-allopyranoside and in (b) L-4-deoxy-4-fluoro-1,3,5-pentyIidyne-myo-inositol.
168
7 Glycosylidene Diazirines
Figure 4. Intermolecular hydrogen-bonding of the carbene derived from the GlcNAc diazirine 14.
4-nitrophenol (2 equiv., 26 "C) reduced the anomeric selectivity to 58 :42 (87% yield). These and analogous observations made by glycosylating the A11NAc-derived diazirine 25 were rationalized by postulating an intermolecular hydrogen-bond from the NHAc group to the glycosyl acceptor (Figure 4). This hydrogen-bond locates the alcohol below the plane of the pyranose ring, well positioned to attack the oxycarbenium and form a-D-glycosides. The hydrogen-bond depends on the conformation of the acetamido group and on the basic properties of the alcohol (higher selectivity with the less acidic, i. e. more strongly basic 2-propanol). The conformation of the acetamido group, in its turn, depends on the configuration (glum or d o ; for a detailed study of the conformational behavior of the NHAc group see Ref. [33]) and the temperature (higher c ~ - D / ~ - Dratio at a higher temperature). The temperature-dependent association of the alcohols explains the much higher yield of the glycosidation of 2-propanol at lower temperature, influenced by the higher basicity of 2-propanol than hexafluoro-2-propanol (better H-bond acceptor) and by the greater acidity of the hydrogen-bond-accepting terminal alcohol unit in a chain of associated alcohols properly located in the o-plane of the carbene (Figure 4). Protonation of the carbene, which depends on the kinetic acidity of the alcohol, is reflected by the higher yields of the hexafluoro-2-propanol- and 4-nitrophenol-derived glycosides. These results confirm the strong influence of hydrogen-bonds on the result of glycosidation and characterize these diazirines as subtle, reactivity-based tools for the investigation of intra- and intermolecular hydrogen-bonds and their influence on regio- and diastereoselective glycosidation.
7.5 Synthesis of Spirocyclopropanes Glycosylidene diazirines react with electrophilic alkenes, e.g. N-phenylmaleimide, acrylonitrile, dimethyl fumarate, dimethyl maleate, and C&-fullerene, to yield spirocyclopropanes with formation of two C-C bonds at the anomeric center [34-371.
7.5 Synthesis of Spirocyclopropanes
R = Bn: So%, 9O:lO R = Piv: 60%. 92: 8
RO
RO
.
,
"'v
169
RO
y0N , P h
Ph
0
22%
BBnO n BnO
70%
Bn ~O- n 0
BnO
52
BnO
BnO Me02C
BBnO n BnO NC
6
,,C02Me
fCo2r"72%
q ..*>CN
CN
Brio%,
C)
O
O OBn CN q BnO
11
31
Brio%. %
Brio BnO
Me BnO BnO
,,C02Me BnO BnO
BnO C02Me
,
C02Me
BnO Me02C
60
40
-
-
29
20
33
1s
le02C
C02Me
[
: 60%
C02Me
d'
z:*,
RRO O+]. RO
'%O
R=Bn:
33%
R=Piv:
72%
Me
24%
'$o
b 9%
14%
Figure 5. Products of the reaction of the benzylated and pivaolyated diazirines 7 and 15 with (a) N-phenylmaleimide, (b) acrylonitrile, (c) dimethyl fumarate and dimethyl maleate, and (d) dihyand 2,3-dihydro-4H-pyran. drofuran, 5-methyl-2,3-dihydrofuran,
Yields depend on the protecting groups; substitution of benzyl by pivaloyl groups reduces yields, in agreement with a reduction of the predominantly nucleophilic character of these ambiphilic carbenes. As illustrated by the cyclopropanation of N-phenylmaleimide, the diastereoisomer with the substituents oriented syn to the glycosyl ring oxygen are formed preferentially (ratio = 90: 10; Figure 5a); cyclopropanation with acrylonitrile confirms this (ratio = 58 :42) and shows that the nitrile function is predominantly located below the average plane of the pyranosyl ring (ratio = 83: 17; Figure 5b). This is confirmed by cyclopropanation of ethyl acrylate [38]; the major isomer, formed in ca 47% yield, has the same configuration as the major isomer resulting from addition to acrylonitrile. The stereoselectivity of cyclopropanation with dimethyl fumarate and dimethyl maleate (Figure 5c) suggests that formation of the two C-C bonds is not concerted; it is rationalized by
170
BnO
7 Glycosylidene Diuzirines
-
BnO BnO
EN pseudoaxial approach
pseudoequatorial approach
Scheme 6. Pseudoaxial and pseudoequatorial. ring closure of the zwitterion obtained upon reaction of acrylonitrile with the carbene derived from 7.
postulating a two-step process with a preferred pseudoaxial trajectory in the formation of the second C-C bond, as illustrated in Scheme 6. In agreement with the ambiphilic character of alkoxycarbenes, glycosylidene carbenes form cyclopropanes also with electron-rich alkoxyalkenes, provided their reactivity is enhanced by ring tension, such as that in dihydrofuran, that leads to 33% (benzylated diazirine 7) or 72% (pivaloylated diazirine 15) of a single isomer (Figure 5d) [39]. Steric hindrance by an additional methyl group reduces the yield. Dihydropyran reacts less readily, and open chain enol ethers lead to low yields only. The 0-benzyl protected diazirines gave lower yields than the 0-pivaolylated analogs. The transition states of the cycloadditions leading to the isomeric cyclopropanes have been calculated (semiempiric program AM1). At the beginning of the reaction, the interaction of the HOMO of the carbene with the LUMO of the enol ether dominates, but in the transition state the interaction between the LUMO of the carbene and the HOMO of the enol ether is more important. The cyclopropanation yields of the pivaloylated diazirine 15 are higher because of the more efficient competing reaction of the 0-benzylated (as compared to the 0-pivaloylated) carbene with the starting diazirine. Azines are isolated as the main by-products. Calculations show that a pseudoaxial attack of the carbene is favored.
7.6 Addition to Aldehydes and Ketones Addition of the benzylated aziglucose 7 to acetone or cyclohexanone, used as solvents, gave 63 and 78%, respectively, of a mixture of anomeric spiroepoxidesin P-D/ a-Dratios of 70 :30 and 65 : 35, respectively (Figure 6a), whereas addition of the A11NAc-derived diazirine 25 to cyclohexanone at 60°C gave 83% of the a-Dconfigured spiroepoxide and a dihydrooxazine formed either directly from the intermediate oxycarbenium cation or by opening
