A highly efficient synthesis of an octasaccharide, the repeating unit of the cell-wall mannan of Trichophyton mentagrophytes and T. rubrum

A highly concise and effective synthesis of the mannose octasaccharide repeating unit of the cell-wall mannan of Trichophyton mentagrophytes and T. rubrum was achieved via 6- O-glycosylation of a tetrasaccharide acceptor with a tetrasaccharide donor, followed by deprotection. The key tetrasaccharide ( 11) was constructed by selective 6- O-glycosylation of allyl 3,4-di- O-benzoyl-α- d-mannopyranosyl-(1→6)-2,3,4-tri- O-benzoyl-α- d-mannopyranoside with 6- O-acetyl-2,3,4-tri- O-benzoyl-α- d-mannopyranosyl trichloroacetimidate, then with 2,3,4,6-tetra- O-benzoyl-α- d-mannopyranosyl trichloroacetimidate. The tetrasaccharide acceptor ( 13) was obtained by selective 6- O-deacetylation of 11, while the tetrasaccharide donor 12 was obtained by deallylation of 11, followed by trichloroacetimidation. Graphic