Stereoselective synthesis of alpha-keto-deoxy-D-glycero-D-galacto-nonulosonic acid glycosides by means of the 4,5-O-carbonate protecting group.

[Image: see text] A 1-adamantyl thioglycoside derivative of KDN, derived from N-acetylneuraminic acid, carrying a 3,4-O-carbonate protecting group is a highy efficient and α-selective KDN donor on activation with NIS and TfOH in dichloromethane and acetonitrile at −78 °C. Glycosylations conducted with this protecting group do not suffer from competing glycal formation. Seven examples are given, including the use of galactose 3- and 6-hydroxy groups.