Chemical Modification of Lactose. XII. Preparation of O-(2-Acetamido-2-deoxy-β-D-glucopyranosyl)-(1→6)-O-β-D-galactopyranosyl-(1→4)-D-glucopyranose (6´-N-Acetylglucosaminyllactose)

Abstract

The title trisaccharide (16) is a constituent of the higher oligosaccharides in human milk. As part of our program of synthesis of oligosaccharides in human milk, the title trisaccharide was prepared. Heating of a mixture of 1, 6-anhydro-2, 2´, 3, 3´, 4´-penta-O-benzyl-β-lactose and 2-methyl-(3, 4, 6-tri-O-acetyl-1, 2-dideoxy-α-D-glucopyrano) [2, 1-d]-2-oxazoline in nitromethane-toluene in the presence of p-toluenesulfonic acid at 95° for 1 hr with stirring afforded the protected 1, 6-anhydro-β-derivative of 16 (6). The protecting groups of 6 were removed by catalytic hydrogenation followed by deacetylation, or vice versa, to afford the 1, 6-anhydro-β-derivative of 16 (9). Compound 9 gave a crystalline peracetate (14). The 1, 6-anhydro-β-ring of 14 was cleaved by mild acetolysis to afford an anomeric mixture of the peracetate of 16, from which the α-anomer (15) was isolated as needles. Deacetylation of 15 gave the title trisaccharide as a hygroscopic amorphous powder.