A facile regio- and stereoselective synthesis of mannose octasaccharide of the N-glycan in human CD2 and mannose hexasaccharide antigenic factor 13b

Abstract

A highly concise and effective synthesis of the mannose octasaccharide of the N-linked glycan in the adhesion domain of human CD2 was achieved via TMSOTf-promoted selective 6-glycosylation of a trisaccharide 4,6-diol acceptor with a pentasaccharide donor, followed by deprotection. The pentasaccharide was constructed by selective 3,6-diglycosylation of 1,2- O-ethylidene-β- d-mannopyranose with 2- O-acetyl-3,4,6-tri- O-benzoyl-α- d-mannopyranosyl-(1→2)-3,4,6-tri- O-benzoyl-α- d-mannopyranosyl trichloroacetimidate, while the trisaccharide was obtained by selective 3-O -glycosylation of allyl 4,6- O-benzylidene-α- d-mannopyranoside with the same disaccharide trichloroacetimidate, followed by debenzylidenation. The mannose hexasaccharide antigenic factor 13b was synthesized by condensation of a trisaccharide donor, 2- O-acetyl-3,4,6-tri- O-benzoyl-α- d-mannopyranosyl-(1→2)-3,4,6-tri- O-benzoyl-α- d-mannopyranosyl-(1→3)-4,6-di- O-acetyl-2- O-benzoyl-α- d-mannopyranosyl trichloroacetimidate, with a trisaccharide acceptor, methyl 3,4,6-tri- O-benzoyl-α- d-mannopyranosyl-(1→2)-3,4,6-tri- O-benzoyl-α- d-mannopyranosyl-(1→2)-3,4,6-tri- O-benzoyl-α- d-mannopyranoside, followed by deprotection.