First synthesis of the immunodominant β-galactofuranose-containing tetrasaccharide present in the cell wall of Aspergillus fumigatus

Abstract

β-Gal f-(1→5)-β-Gal f-(1→6)-α-Man p-(1→6)-α-Man p, the immunodominant epitope in the cell-wall galactomannan of Aspergillus fumigatus, was synthesized for the first time as its allyl glycoside. The key disaccharide glycosyl donor, 2,3,5,6-tetra- O-benzoyl-β- d-galactofuranosyl-(1→5)-2- O-acetyl-3,6-di- O-benzoyl-β- d-galactofuranosyl trichloroacetimidate ( 10), was constructed by 5- O-glycosylation of 1,2- O-isopropylidene-3,6-di- O-benzoyl-α- d-galactofuranose ( 4) with 2,3,5,6-tetra- O-benzoyl-β- d-galactofuranosyl trichloroacetimidate ( 5), followed by 1,2- O-deacetonation, acetylation, selective 1- O-deacetylation, and trichloroacetimidation. The target tetrasaccharide 16 was obtained by the condensation of allyl 2,3,4-tri- O-benzoyl-α- d-mannopyranosyl-(1→6)-2,3,4-tri- O-benzoyl-α- d-mannopyranoside ( 14) as glycosyl acceptor with the disaccharide glycosyl donor 10, followed by deprotection.