CARB 8 |
| The majority of biologically important carbohydrates exist as polysaccharides or glycoconjugates in which monosaccharide units are joined together via O-glycosidic bonds. The necessity to form either alpha- or beta-glycosidic bond with complete stereoselectivity is the main reason chemical O-glycosylation is placed among the most challenging problems of modern synthetic chemistry. The last two decades have witnessed an explosive growth of the field of glycobiology, which resulted in the appreciation and understanding of deep involvement of complex carbohydrates in vital biological processed. The importance of chemical and/or enzymatic synthesis of complex saccharides has come to the fore because of the low availability of pure glycostructures from natural sources. Despite enormous progress in the area of synthetic carbohydrate chemistry, no general glycosylation approach for efficient and stereoselective oligosaccharide synthesis in solution and on a polymer support has yet emerged. As a part of the program to develop novel, versatile methods and strategies for oligosaccharide synthesis, we reported the synthesis of the S-benzoxazolyl (SBox) glycosides and their evaluation as glycosyl donors. Further extension of this methodology has emerged with the development of novel S-thiazolyl derivatives (STaz), stable and versatile glycosyl donors. Overall, we have demonstrated that glycosyl donors with a generic leaving group SCR1=NR2 (substituted thioimidoyl derivatives) provide very high stereoselectivity and remarkably high yields. Here further expansion of the thioimidate glycosylation methodology to convergent saccharide synthesis will be discussed. |
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Frontiers in Modern Carbohydrate Chemistry
1:30 PM-5:00 PM, Sunday, 13 March 2005 San Diego Marriott -- San Diego A, Oral
Division of Carbohydrate Chemistry |