Synthesis of benzyl 2-acetamido-3-O- and -6-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-2-deoxy-α-d-galactopyranoside

Glycosylation of benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-α-d-galactopyranoside with 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl bromide in dichloromethane, in the presence of silver trifluoromethanesulfonate, 2,4,6-trimethylpyridine, and molecular sieves, afforded benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-3-O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-α-d-galactopyranoside (3). Cleavage of the benzylidene group of 3 gave benzyl 2-acetamido-2-deoxy-3-O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-α-d-galactopyranoside (4), which, on deacylation, followed by peracetylation, furnished the peracetylated disaccharide derivative (7). The structures of 3, 4, and 7 were established by ¹H-n.m.r. spectroscopy. O-Deacetylation of 7 afforded the title β-(1→3)-linked disaccharide (8). Compound 3 was also deacylated and then peracetylated, to give benzyl 2-acetamido-3-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-β-d-glucopyranosyl)-4,6-O-benzylidene-2-deoxy-α-d-galactopyranoside, which was O-deacetylated to give its 4,6-O-benzylidene derivative (6). For the synthesis of the β-(1→6)-linked disaccharide, the readily accessible benzyl 2-acetamido-3-O-acetyl-2-deoxy-α-d-galactopyranoside was condensed with 2-methyl-(3,4,6-tri-O-acetyl-1,2-dideoxy-α-d-glucopyrano)-[2,1-d]-2-oxozaline, and the product was isolated as its peracetylated derivative, which, on saponification, afforded the title β-(1→6)-linked disaccharide (12). The structures of compounds 6, 8, and 12 were established by ¹³C-n.m.r. spectroscopy.