Practical synthesis of a tetrasaccharide derivative corresponding to ristomycin A and ristocetin A

Abstract

A practical synthesis of fully benzoylated tetrasaccharide, whose free form is indispensable to the antibiotic ristomycin A for the process of dimerization and binding to the cell wall, was achieved via sequential assembly of the building blocks, allyl 3,4-di- O-benzoyl-α- d-glucopyranoside, 2,3,4-tri -O-benzoyl-α- l-rhamnopyranosyl trichloroacetimidate, 2- O-acetyl-3,4,6-tri- O-benzoyl-α- d-mannopyranosyl trichloroacetimidate, and 2,3,5-tri- O-benzoyl-α- d-arabinofuranosyl trichloroacetimidate. A one-pot preparation of allyl 3,4-di- O-benzoyl-2- O- tert-butyldimethylsilyl-6- O-triphenylmethyl-α- d-glucopyranoside is described, and regioselective glycosylation is carried out using perbenzoylated sugar trichloroacetimidates as glycosyl donors in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate (TMSOTf).