Synthetic Mucin Fragments: Methyl-3-O-(2-acetamido-2-deoxy-4-o-and 6-O-β-D-Galactopyranosyl-β-D-Glucopyranosyl)-β-D-Galactopyranoside And Methyl 3-O-(2-Acetamido-2-Deoxy-4-O-and 3-O-Methyl-β-D-Glucopyranosyl-β-D-Galactopyranoside

Glycosylation of methyl 3-O-(2-acetamido-3,6-di-O-benzyl-2-deoxy-β-D-glucopyranosyl)-2,4,6-tri-O-benzyl-β-D-galactopyranoside (2) with 3,4,6-tetra-O-acetyl-α-D-galactopyranosyl bromide (1), catalyzed by mercuric cyanide, afforded a trisaccharide derivative, which was not separated, but directly O-deacetylated to give methyl 3-O-(2-acetamido-3,6-di-O-benzyl-2-deoxy-4-O-β-D-galactopyranosyl-β-D-glucopyranosyl)-2,4,6-tri-O-benzyl-β-D-galactopyranoside (8). Hydrogenolysis of the benzyl groups of 8 then furnished the title trisaccharide (9). A similar glycosylation of methyl 3-0-(2-acetamido-3-O-acetyl-2-deoxy-β-D-glucopyranosyl)-2,4,6-tri-O-benzyl-β-D-galactopyranoside (obtained by acetylation of 4, followed by hydrolysis of the benzylidene acetal group) with bromide 1 gave a tribenzyl trisaccharide, which, on catalytic hydrogenolysis, furnished the isomeric trisaccharide (12). Methylation of 4 and 2 with methyl iodide-silver oxide in 1:1 dichloro-methane-N, N-dimethylformamide gave the 3-0-and 4-0-monomethyl ethers (13) and (15), respectively. Hydrogenolysis of the benzyl groups of I3 and 15 then provided the title monomethylated disaccharides (14) and (16), respectively. The structures of trisaccharides 9 and 12, and disaccharides 14 and 16 were all established by by, ¹³C NMR spectroscopy.