Ready access to a branched Man5 oligosaccharide based on regioselective glycosylations of a mannose-tetraol with n-pentenyl orthoesters.

A branched Man(5) oligosaccharide has been synthesized by sequential regioselective glycosylations on a mannose-tetraol with n-pentenyl orthoester glycosyl-donors promoted by NIS/BF(3)·Et(2)O, in CH(2)Cl(2). An extended n-pentenyl chain was incorporated into the tetraol acceptor to facilitate (a) the solubility of the starting tetraol in CH(2)Cl(2), and (b) future manipulations at the reducing end of the Man(5) oligosaccharide.