Synthesis of neoglycolipids containing a mucin-type core unit

The unnatural glycolipids O-β-d-galactopyranosyl-(1→4)-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-O- (2-acetamido-2-deoxy-α-d-galactopyranosyl)-(1→1)-ceramide (1), O-β-d-galactopyranosyl-(1→4)-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→6)-O-(2-acetamido-2-deoxy-β-d -glucopyranosyl)-(1→6)-O-(2-acetamido-2-deoxy-α-d-galactopyranosyl)-(1→1)-ceramide (2), and O-β-d-galactopyranosyl (1→4)-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-O-[O-β-d-galactopyranosyl (1→4)-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→6)]-O-(2-acetamido-2-deoxy-α-d-galactopyranosyl)(1→1)-ceramide (3), and their β-(1→1)-linked isomers, were synthesized. The precursor oligosaccharides for 1, 2, and 3 were made by coupling O-(2,3,4,6-tetra-O-acetyl-β-D- galactopyranosyl)-(1→4)-3,6-di-O-acetyl-2-deoxy-2-phthalimido-α,β-d-glucopyranosyl trichloroacetimidate with tert-butyldiphenylsilyl 2-azido-4,6-O-benzylidene-2-deoxy-β-d-galactopyranoside, tert-butyldiphenylsilyl 2-azido-3-O-benzoyl-2-deoxy-β-d-galactopyranoside, and tert-butyldiphenylsilyl O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-(1→4)-O-(3,6-di-O-acetyl-2-deoxy- 2-phthalimido-β-d-glucopyranosyl)-(1→3)-2-azido-2-deoxy-β-d-galactopyranoside, respectively. These oligosaccharides were converted into their trichloroacetimidates, which were coupled with 3,2′-di-O-benzoyl ceramide. Deprotection of the coupling products gave the title compounds 1, 2, and 3.