Synthetic Studies of Glycopeptides and Glycoconjugates
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SYNTHETIC STUDIES OF GLYCOPEPTIDES AND GLYCOCONJUGATES by NING SHAO Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Thesis Advisor: Dr. Zhongwu Guo Department of Chemistry CASE WESTERN RESERVE UNIVERSITY May, 2005 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the dissertation of ______________________________________________________ candidate for the Ph.D. degree *. (signed)_______________________________________________ (chair of the committee) ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ (date) _______________________ *We also certify that written approval has been obtained for any proprietary material contained therein. To my parents, grandma, and my wife, Feng Table of Contents List of Schemes v List of Tables vii List of Figures viii Acknowledgements ix List of Abbreviations x Abstract xiv Chapter 1. Synthetic Studies of Glycopeptides and Glycoproteins 1.1 Introduction 2 1.2 Structures of N- and O-Linked Glycoproteins 2 1.2.1 The N-Linked Glycoproteins 3 1.2.2 The O-Linked Glycoproteins 4 1.3 The Microheterogeneity of Glycoproteins 6 1.4 Chemical Syntheses of Glycopeptides and Glycoproteins—A Significant Challenge 8 1.5 Synthesis of Glycopeptides Using Protected Glycosyl Amino Acids as Building Blocks 11 1.5.1 Synthesis of N-Linked Glycopeptides 11 1.5.2 Synthesis of O-Linked Glycopeptides 15 1.6 Synthesis of Glycopeptides Using Glycosyl Amino Acids Containing Unprotected Oligosaccharide Moieties 17 i 1.6.1 Synthesis of N-Linked Glycopeptides Using Unprotected Glycosyl Amino Acids as Building Blocks 18 1.6.2 Convergent Synthesis of N-Glycopeptides by Conjugation of Carbohydrate Amines to Full-Length Peptides 20 1.6.3 Synthesis of Glycopeptides by Solution-Phase Synthesis with Solid-Phase Workup 23 1.6.4 Synthesis of Glycoproteins by Polymerization of Glycopeptides 27 1.6.5 Synthesis of Glycoproteins by Native Chemical Ligation 27 1.7 Conclusion 29 1.8 References 30 Chapter 2. Solution-Phase Synthesis of O-Linked Glycopeptides with Solid-Phase Workup---Synthesis of Asialoglycophorin AM Glycopeptides with Clusters of TF antigen 2.1 Introduction 38 2.2 Synthetic Strategy 40 2.3 Synthesis of the Disaccharide Glycosyl Donor 42 2.4 Synthesis of the Glycosyl Amino Acid 47 2.5 Protecting Group Manipulation 50 2.6 Glycopeptide Synthesis by SSSW 51 2.7 Efforts to Couple the Glycopeptide Fragments 2.2 and 2.3 Together 54 2.8 Conclusion 55 2.9 Experimental Section 56 2.10 References 80 ii Chapter 3. Synthesis of CD52 Glycopeptide Containing an Acid-Labile Fucosyl Linkage 3.1 Introduction 84 3.2 Retrosynthetic Analysis 85 3.3 Synthesis of the Properly Protected Monosaccharides 86 3.4 Synthesis of the Glycosyl Amino Acids with Free Sugar Moiety 87 3.5 Synthesis of A Glycohexapeptide Fragment of CD52 using SSSW 90 3.6 Synthesis of CD52 Glycopeptide 3.1 by SSSW 94 3.7 Conclusion 96 3.8 Experimental Section 98 3.9 References 116 Chapter 4. Solid-Phase Synthesis of CD52 Glycopeptides and Their Application to the Synthesis of CD52 Antigen 4.1 Introduction 118 4.2 Retrosynthetic Plan for Synthesis of a Skeleton Structure of Sperm CD52 119 4.3 Synthesis of the Fully Protected Glycopeptide 4.2 122 4.3.1 Synthesis of the Monosaccharide Building Blocks 122 4.3.2 Synthesis of the Fucosylated N-Linked Core Oligosaccharide and its Asn Conjugate 124 4.3.3 Solid-Phase Synthesis of CD52 Glycopeptide 3.1 127 4.3.4 Solid-Phase Synthesis of the Fully Protected Glycopeptide 4.2 130 4.3.5 Synthesis of the Skeleton Structure of CD52 Antigen 131 iii 4.4 Conclusion 134 4.5 Experimental Section 135 4.6 References 158 Appendix 161 Bibilography 211 iv List of Schemes Scheme 1.1 Some potential side reactions during the final deprotection of glycopeptides 9 Scheme 1.2 Solid-phase synthesis of CD52 glycopeptide 12 X Scheme 1.3 Synthesis of glycosyl amino acid with an arabinosialyl Lewis structure 13 Scheme 1.4 Solid-phase synthesis of ESL-1 glycopeptide with an arabino sialyl X Lewis Structure 14 Scheme 1.5 Solution-phase synthesis of O-glycopeptides with trivalent TF antigen 16 Scheme 1.6 Solid-phase synthesis of O-glycopeptides with trivalent TF antigens 17 Scheme 1.7 Solution-phase synthesis of N-linked glycopeptides using building blocks containing free sugar moieties 19 Scheme 1.8 Solid-phase synthesis of an N-linked glycopeptide using building blocks containing free sugar moieties 20 Scheme 1.9 Convergent synthesis of N-glycopeptides by fragment coupling 21 Scheme 1.10 Lansbury’s approach for convergent synthesis of N-glycopeptide 22 Scheme 1.11 Danishefsky’s synthesis of hybride-type gp 120 fragment glycopeptide 23 Scheme 1.12 SSSW synthesis of glycopeptides by N-terminal elongation 25 Scheme 1.13 SSSW synthesis of glycopeptides: a) C-terminal elongation; b) multivalent glycopeptides 26 Scheme 1.14 Synthesis of an antifreeze glycoprotein by glycopeptide polymerization 27 Scheme 1.15 Synthesis of an N-glycopeptide by native chemical ligation 29 Scheme 2.1 Retrosynthetic analysis of 2.1 40 Scheme 2.2 The two routes to synthesize O-linked glycosyl amino acid 41 v Scheme 2.3 Synthesis of the disaccharyl TCA donor from galactosamine 42 Scheme 2.4 Synthesis of the disaccharide glycal 2.23 using glycosyl fluoride donor 44 Scheme 2.5 Possible explanation of the glycosylation reaction 46 Scheme 2.6 Synthesis of glycosyl fluoride 2.33 from disaccharide glycal 2.23 47 Scheme 2.7 Glycosylation using a benzylidene protected fluoride donor 50 Scheme 2.8 Deprotection of 2.38 and 2.39 to get glycosyl amino acids with unprotected sugar moiety 51 Scheme 2.9 Synthesis of glycopeptide 2.46 using SSSW 52 Scheme 2.10 Synthesis of glycopeptide fragment 2.49 using SSSW 54 Scheme 2.11 Chemical fragment coupling reactions----efforts to synthesize 2.1 55 Scheme 3.1 Synthesis of monosaccharide building blocks 86 Scheme 3.2 Synthesis of the trisaccharide glycan 88 Scheme 3.3 Synthesis of the glycosyl amino acid with a free sugar moiety 89 Scheme 3.4 Synthesis of glycohexapeptide fragment by SSSW 91 Scheme 3.5 Synthesis of CD52 glycopeptide 3.1 94 Scheme 4.1 Retrosynthetic plan for a skeleton structure of CD52 4.1 120 Scheme 4.2 Retrosynthesis of the protected CD52 glycopeptide 4.2 122 Scheme 4.3 Synthesis of the monosaccharide building blocks 123 Scheme 4.4 Synthesis of the key β-mannodisaccharide donor 124 Scheme 4.5 Synthesis of the glycosyl amino acid building block 126 Scheme 4.6 Solid-phase synthesis of CD52 glycopeptide 3.1 129 Scheme 4.7 Solid-phase assembly of the fully protected glycopeptide 4.2 130 Scheme 4.8 Synthesis of the skeleton structure of CD52 antigen 4.1 133 vi List of Tables Table 2.1 Synthesis of the disaccharide glycal 2.23 using glycosyl TCA donor 45 Table 2.2 Glycosylation of amino acids by different glycosyl donors 48 Table 2.3 Glycosylation using acetyl protected disaccharides as donors 49 vii List of Figures Figure 1.1 Three subgroups of N-linked type glycan structure: (a) complex type; (b) high mannose type; (c) hybrid type 4 Figure 1.2 Core glycan structures of mucin glycoproteins 5 Figure 1.3 Some tumor-associated carbohydrate antigens 6 Figure 1.4 Solution-phase glycopeptide synthesis with solid-phase workup 24 Figure 1.5 The principle of native chemical ligation 28 Figure 2.1 The N-terminal structure of asialoglycophorin AM 38 Figure 2.2 Glycophorin A and asialoglycophorin A with M and N blood group specificities 39 Figure 3.1 The key disconnection of retrosynthetic analysis of glycopeptide 3.1 85 1 Figure 3.2 H NMR spectra of the crude and purified glycohexapeptide 3.25 (D2O, 600 MHz) 93 Figure 3.3 HPLC diagrams of the final product 3.1: (a) SSSW synthesis using pfpOH/DCC; (b) SSSW synthesis using HOBt/DCC 95 1 Figure 3.4 H NMR and HMQC spectra of the CD52 glycopeptide 3.1 (D2O, 600 MHz) 97 Figure 4.1 A representative sperm CD52 structure 119 Figure 4.2 HPLC diagram of the CD52 glycopeptide 3.1 prepared by solid-phase synthesis 129 Figure 4.3 1H NMR and HMQC spectrum of fully protected glycopeptide 4.2 (CDCl3, 600 MHz) 132 viii Acknowledgements I would like to express my deepest regards and sincere gratitude to Professor Zhongwu Guo for his guidance, enthusiasm and support. I really appreciate his constant encouragement throughout my Ph. D studies, his faith in the abilities of the students and his ready availability on all matters. He is not only a helpful advisor, but also a dear friend. Professor Michael Zargoski, Anthony J. Pearson and Robert G. Salomon are gratefully acknowledged for taking time to serve on my Ph. D. committee. I am grateful to all my labmates, past and present for the helpful discussions and providing a friendly environment to work and study. My special thanks go to Dr. Jie Xue for his help on many things. We collaborated very well on the projects and I learned a lot from him. I need to thank my parents and my grandma who always supported me in every step of my life. No matter whether they understand it or not, especially my grandma, they always trusted me so I could pursue my ambition with confidence. Although they were not here with me all these years, I can always feel their love right by my side. I also would not have made it through my Ph. D. study without the love and support of my wife, Feng. She was always there with me, helping me and encouraging me, so I can resume my confidence in spite of frustrations and continue to work through it.