Stereoselective Synthesis of S-Linked Hexasaccharide of Landomycin A via Umpolung S-Glycosylation.

Stereoselective synthesis of carbohydrate mimics resistant toward acid-mediated or enzymatic hydrolysis is chemically challenging and biologically interesting. In this Letter, the first stereoselective synthesis of a "non-hydrolyzable" S-linked hexasaccharide of antitumor antibiotic landomycin A is described. This synthesis was accomplished through the utilization of our recently developed umpolung reactivity-based S-glycosylation-sulfenylation of stereochemically defined glycosyl lithium species with asymmetric sugar-derived disulfides.