Chemical Modification of Lactose. IX. Synthesis of O-β-D-Galactopyranosyl-(1→6)-O-β-D-galactopyranosyl-(1→4)-D-glucopyranose (6'-Galactosyllactose)

Abstract

The title trisaccharide was synthesized from 1, 6-anhydro-β-lactose. Condensation of 2, 2', 3, 3'-tetra-O-acetyl-1, 6-anhydro-β-lactose and 2, 3, 4, 6-tetra-O-acetyl-α-D-galactopyranosyl bromide by a modified Koenigs-Knorr reaction followed by acetylation gave acetylated 1, 6-anhydro-β-trisaccharide (3) in 62% yield. The β-configuration for the new galactosidic linkage was obtained from the value of the molecular rotation of 3. Deacetylation of 3 afforded 1, 6-anhydro-β-trisaccharide (4). The structure was determined by a gas chromatographic (GC) analysis and a gas chromatography-mass spectrometry of acid hydrolysate of permethylated 4. Acetolysis of 3 under mild condition proceeded cleavage of the 1, 6-anhydro-β-ring and afforded acetylated trisaccharide contaminated with acetylated galactose and lactose. From the acetolysis mixture, the title trisaccharide was isolated via acetylated β-trisaccharide followed by deacetylation. The structure was determined by GC analysis of the partial methylated alditol acetates obtained from the hydrolysate of permethylated, borohydride reduced trisaccharide.