? Molecules containing glycosidic bonds (e.g., oligosaccharides and nucleosides) are ubiquitous in nature and these species play critical roles in an enormous number of medically-relevant biological events ranging from fertilization to inflammation to bacterial and viral infection to cancer metastasis. These species can generally only be isolated in very small amounts from natural sources. Therefore, access to the quantities needed for detailed biological or medical studies requires efficient methods for their chemical synthesis. Despite significant advances over the last twenty years in the area of glycoside bond assembly, these molecules remain challenging synthetic targets. There is a continuing need for new methods for the preparation of glycosidic bonds, and the long-term objective of this project is to explore a fundamentally new class of glycosylating agent. In particular, we will investigate the ability of thioglycosides and glycosyl sulfoxides possessing epoxide and cyclopropane functionality to glycosylate alcohols in a highly stereoselective fashion.
The specific aims of this proposal are: 1.) To explore the use of 2,3-anhydrofuranosyl donors in the synthesis of O-glycosides and nucleosides. 2.) To extend these studies to compounds in which the epoxide ring has been replaced by a cyclopropane moiety. 3.) To probe the mechanism of these glycosylations through the combined use of NMR and IR-spectroscopy as well as computational methods. 4.) To explore the scope of a highly stereoselective glycosylation reaction of 2,3-anhydrosugar thioglycosides, which occurs with concomitant migration of the sulfur from the anomeric center affording 2-thioaryl glycosides; the use of the analogous selenoglycosides will also be explored. 5.) To apply the methodology developed in Specific Aims 1-4 to the synthesis of selected target molecules. ? ?
