Catalytic stereoselective glycosidation with glycosyl diphenyl phosphates: Rapid construction of 1,2-cis-alpha-glycosidic linkages

A commercially available 0.1 M solution of HClO4 in dioxane has been shown to catalyze the glycosidation of glycosyl diphenyl phosphates. The per-O-benzyl-protected glucosyl and galactosyl donors and the 3,4,6-tri-O-acetyl-2-azido-2-deoxygalactosyl donor each react with a range of acceptor alcohols in the presence of 0.05-0.2 equiv of HClO4, in dioxane/Et2O (1:1) to afford glycosides in good yields with good to excellent alpha selectivities, The synthetic utility of this glycosidation method was demonstrated by a stereoselective synthesis of the a-galactosylceramide KRN7000, an activator of natural killer (NK) T cells through CD1d molecules.