Stereocontrolled construction of 1,2-cis-α-glycosidic linkages using glycosyl diphenyl phosphates and synthesis of α-galactosylceramide KRN7000

The development of a general stereoselective method for 1,2-cis-α-glycosidations remains an important issue for synthesis in carbohydrate chemistry. Recently, we have achieved a highly stereocontrolled construction of 1,2-cis-α-glycosidic linkages using glycosyl diphenyl phosphates as glycosyl donors. 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 high α-selectivities. The synthetic utility of the present glycosidation method was demonstrated by a stereoselective synthesis of the α-galactosylceramide KRN7000, an activator of natural killer (NK) T cells through CD1d molecules.