Synthetic mucin fragments: methyl 3-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-β-d-galactopyranoside and methyl 3-O-(2-acetamido-2-deoxy-3-O-β-d-galactopyranosyl-β-d-glucopyranosyl)-β-d-galactopyranoside

Methyl 2,4,6-tri-O-benzyl-β-d-galactopyranoside (5) was obtained crystalline by way of its 3-O-allyl derivative, which was in turn obtained by ring-opening of a presumed 3,4-O-stannylene derivative of methyl β-d-galactopyranoside, followed by benzylation. Condensation of 5 with 2-methyl-(2-acetamido-3,4,6-tri-O-acetyl-1,2-dideoxy-β-d-glucopyrano)-[2,1-d]-2-oxazoline in 1,2-dichloroethane in the presence of p-toluenesulfonic acid afforded the disaccharide derivative methyl 3-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-β-d-glucopyranosyl)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (6). Deacetylation of 6 in methanolic sodium methoxide afforded the disaccharide derivative 7, which was acetalated with α,α-dimethoxytoluene to afford the 4′,6′-O-benzylidene acetal (10). Catalytic hydrogenolysis of the benzyl groups of 7 afforded the title disaccharide 8. Glycosylation of 10 with 2,3,4,6-tetra-O-acetyl-α-d-galactopyranosyl bromide in 1:1 benzenenitromethane in the presence of mercuric cyanide gave the fully protected trisaccharide derivative 12. Systematic removal of the protecting groups of 12 then furnished the title trisaccharide 14. The structures of 5, 8 and 14 were all confirmed by ¹³C-n.m.r. spectroscopy. The ¹³C-n.m.r. chemical shifts for methyl α- and β-d-galactopyranoside, and also those of their 3-O-allyl derivatives, are recorded, for the sake of comparison, in conjunction with those of compound 5.