Synthesis of some d-mannosyl-oligosaccharides containing the methyl and 4-nitrophenyl β-d-mannopyranoside units

Methyl 3,4,6-tri-O-benzyl-β-d-mannopyranoside (2), methyl 2,3-O-isopropylidene-β-d-mannopyranoside (11), and 4-nitrophenyl 2,3-O-isopropylidene-β-d-mannopyranoside (12) were each condensed with 2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl bromide (1) in the presence of mercuric cyanide, to give after deprotection, methyl 2- (5) and 6-O-α-d-mannopyranosyl-β-d-mannopyranoside (15), and 4-nitrophenyl 6-O-α-d-mannopyranosyl-β-d-mannopyranoside (20), respectively. A similar condensation of 11 with 3,4,6-tri-O-acetyl-2-O-(2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl)-α-d-mannopyranosyl bromide (21) and 2,3,4-tri-O-acetyl-6-O-(2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl)-α-d-mannopyranosyl bromide (25), followed by removal of protecting groups, afforded methyl O-α-d-mannopyranosyl-(1 → 2)-O-α-d-mannopyranosyl-(1 → 6)-β-d-mannopyranoside (24) and methyl O-α-d-mannopyranosyl-(1 → 6)-O-α-d-mannopyranosyl-(1 → 6)-β-d-mannopyranoside (28), respectively. Bromide 25 was also condensed with 12 to give a trisaccharide derivative which was deprotected to furnish 4-nitrophenyl O-α-d-mannopyranosyl-(1 → 6)-α-d-mannopyranosyl-(1 → 6)-β-d-mannopyranoside (31). Phosphorylation of methyl 3,4,6-tri-O-benzyl-2-O-α-d-mannopyranosyl-β-d-mannopyranoside and 15 with diphenyl phosphorochloridate in pyridine gave the 6′-phosphates 6 and 16, respectively. Hydrogenolysis of the benzyl and phenyl groups provided methyl 2-O-(disodium α-d-mannopyranosyl 6-phosphate)-β-d-mannopyranoside (7) and methyl 6-O-(disodium α-d-mannopyranosyl 6-phosphate)-β-d-mannopyranoside (17) after treatment with Amberlite IR-120 (Na⁺) cation-exchange resin. The structures of compounds 5, 7, 15, 17, 20, 24, 28, and 31 were established by ¹³C-n.m.r. spectroscopy.