Synthesis of O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-O-β-d-galactopyranosyl-(1→4)-2-acetamido-2-deoxy-d- glucopyranose and two related trisaccharides containing the "lacto-N-biose II" unit

Condensation of 3-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-β-d-glucopyranosyl)-2,4,6-tri-O-acetyl-α-d-galactopyranosyl bromide (1) with benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-α-d-glucopyranoside in boiling benzene and in the presence of mercuric cyanide afforded a trisaccharide that was O-deacetylated to give benzyl O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-O-β-d-galactopyranosyl-(1→4)-3,6-di-O-benzyl-2-deoxy -α-d-glucopyranoside, the benzyl groups of which were cleaved by catalytic hydrogenolysis to furnish the title trisaccharide. Alternatively, bromide 1 was allowed to react with 2-acetamido-1,6-anhydro-3-O-benzyl-2-deoxy-β-d-glucopyranose in 1:1 benzene-nitromethane in the presence of mercuric cyanide, followed by O-deacetylation, column chromatography, and reacetylation to give O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-β-d-glucopyranosyl)-(1→3)-O-(2,4,6-tri-O-acetyl-β-d- galactopyranosyl)-(1→4)-2-acetamido-1,6-anhydro-3-O-benzyl-2-deoxy-β-d-glucopyranose. Acetolysis, followed by catalytic hydrogenation and subsequent O-deacetylation furnished the title trisaccharide. A similar condensation of bromide 1 with 4-nitrophenyl 2-acetamido-2-deoxy-4,6-O-(4-methoxybenzylidene)-β-d-glucopyranoside and 2-nitrophenyl 2-acetamido-2-deoxy-4,6-O-(4-methoxybenzylidene)-α-d-galactopyranoside produced two trisaccharide derivatives, the acetal groups of which were cleaved in hot, 60% aqueous acetic acid, and the resulting diol intermediates O-deacetylated to furnish the desired trisaccharides 4-nitrophenyl O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-O-β-d-galactopyranosyl)-(1→3)-2- acetamido-2-deoxy-β-d-glucopyranoside and 2-nitrophenyl O-(2-acetamido-2-deoxy-β-d-glucopyranosyl-(1→3)-O-β-d-galactopyranosyl-(1→3)-2-acetamido-2-deoxy-β-d- galactopyranoside.