Synthesis of two oligosaccharides, the GPI anchor glycans from S. cerevesiae and A. fumigatus Original Research Article

Two oligosaccharides, α-d-Manp-(1 → 2)-α-d-Manp-(1 → 2)-α-d-Manp-(1 → 6)-α-d-Manp-(1 → 4)-α-d-GlcpNAc () and α-d-Manp-(1 → 3)-α-d-Manp-(1 → 2)-α-d-Manp-(1 → 2)-α-d-Manp-(1 → 6)-α-d-Manp-(1 → 4)-α-d-GlcpNAc (), the glycosylphosphatidylinositol (GPI) anchor glycans from S. cerevesiae and A. fumigatus were synthesized as their methyl glycosides in a regio- and stereoselective manner. The pentasaccharide was obtained from 6-O-selective glycosylation of methyl 2,3-di-O-benzoyl-α-d-mannopyranosyl-(1 → 4)-2-acetamido-3,6-di-O-benzoyl-2-deoxy-α-d-glucopyranoside () 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 (), followed by benzoylation, deacetylation, and mannosylation, and then by deprotection. The hexasaccharide () was obtained via condensation of allyl 3,4,6-tri-O-benzoyl-α-d-mannopyranosyl-(1 → 2)-3,4,6-tri-O-benzoyl-α-d-mannopyranoside () with 2,3,4,6-tetra-O-benzoyl-α-d-mannopyranosyl-(1 → 3)-2,4,6-tri-O-acetyl-α-d-mannopyranosyl trichloroacetimidate (), followed by deallylation, trichloroacetimidation, and coupling with acceptor (), and finally by deprotection.