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

A practical synthesis of fully benzoylated tetrasaccharide, whose free form is indispensable to the antibiotic ristomycin A for the process of dimeriz ation and binding to the cell wall, was achieved via sequential assembly of the building blocks, allyl 3,4-di-O-benzoyl-alpha -D-glucopyranoside, 2,3, 4-tri-0-benzoyl-alpha -L-rhamnopyranosyl trichloroacetimidate, 2-O-acetyl-3 ,4,6-tri-O-benzoyl-alpha -D-mannopyranosyl trichloroacetimidate, and 2,3,5- tri-O-benzoyl-alpha -D-arabinofuranosyl trichloroacetimidate. A one-pot pre paration of allyl 3,4-di-O-benzoyl-2-O-tertbutyldimethylsilyl-6-O-triphenyI methyl-a is described, and regioselective glycosylation is carried out usin g perbenzoylated sugar trichloroacetimidates as glycosyl donors in the pres ence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate (TMS OTf). (C) 2001 Elsevier Science Ltd. All rights reserved.