APPLICATION OF BORONIC-ACID-CATALYZED GLYCOSYLATION TO LATE-STAGE MODIFICATION OF NATURAL GLYCOSIDES AND OLIGOSACCHARIDE SYNTHESIS

摘要

The late-stage modification of biologically active natural glycosides has led to the development of a large amount of novel therapeutic agents. Therefore, intensive effort has been directed toward the development of catalyst-controlled regioselective functionalization [1] of natural glycoside. Particularly, from a standpoint of glycodiversification, a regio- and stereoselective glycosylation method has been desirable because the biological activity of natural glycosides is often influenced by the anomeric configuration [2]. Therefore, several regio- and 1,2-trans-stereoselective glycosylations [3] of natural glycosides have been developed, however, no regio- and 1,2-cis-stereoselective glycosylation of natural glycoside has been reported. In this context, we have recently developed a boronic acid catalyzed regio- and 1,2-cis-stereoselective glycosylation of unprotected sugar acceptors. Herein we wish report its application to a direct regio- and 1,2-cis-stereoselective glycosylation of unprotected natural glycosides and the synthesis of branched a-glucan 11.