Regioselective syntheses of galactosyl oligosaccharides with β-galactosidase from Bifidobacterium bifidum

Abstract

β-Galactosidase from Bifidobacterium bifidum was used to catalyze the transfer of β-D-galactopyranosyl from 4-nitrophenyl-D-galactopyranoside to a hydroxyl group of 2-acetamido-2-deoxy-galactopyranose and 3-O-methyl-D-glucopyranose in the synthesis of Gal(β 1-4)GlcNAc, Gal(β 1-6)GlcNAc and Gal(β 1-6)3-O-Me-Glc in triethyl phosphate buffered solution. When 2-acetamido-2-deoxy-galactopyranose was used as acceptor the 1-4 linked disaccharide was the major product. However, when 3-O-methyl-D-glucopyranose was used as acceptor the 1-6 linked disaccharide was exclusively produced. Even blocking of the C-6 hydroxyl group with acetyl group could not change the regioselectivity of β-galactosidase from Bifidobacterium bifidum when 3-O-methyl-D-glucopyranose was used as the acceptor. In addition, immobilized β-galactosidase (B. bifidum) on nylon powder 6 was stable and could be used repeatedly for the synthetic work.