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The tetrasaccharide repeating unit of Escherichia coli O9a, α-d-Manp-(1→2)-α-d-Manp-(1→3)-α-d-Manp-(1→3)-d-Manp, and the pentasaccharide repeating unit of E. coli O9 and Klebsiella O3, α-d-Manp-(1→2)-α-d-Manp-(1→2)-α-d-Manp-(1→3)-α-d-Manp-(1→3)-d-Manp, were synthesized as their methyl glycosides. Thus, selective 3-O-allylation of p-methoxyphenyl α-d-mannopyranoside via a dibutyltin intermediate gave p-methoxyphenyl 3-O-allyl-α-d-mannopyranoside (2) in good yield. Benzoylation (→3), then removal of 1-O-methoxyphenyl (→4), and subsequent trichloroacetimidation afforded the 3-O-allyl-2,4,6-tri-O-benzoyl-α-d-mannopyranosyl trichloroacetimidate (5). Condensation of 5 with methyl 4,6-O-benzylidene-α-d-mannopyranoside (6) selectively afforded the (1→3)-linked disaccharide 7. Benzoylation of 7, debenzylidenation, benzoylation, and deallylation gave methyl 2,4,6-tri-O-benzoyl-α-d-mannopyranosyl-(1→3)-2,4,6-tri-O-benzoyl-α-d-mannopyranoside (11) as the disaccharide acceptor. Coupling of 11 with (1→2)-linked mannose disaccharide donor 17 or trisaccharide donor 21, followed by deacylation, furnished the target tetrasaccharide and pentasaccharide, respectively. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]