Kinetic control of regioselectivity in glycosidase-catalysed disaccharide synthesis: preparation of 2-acetamido-4-O-(2-acetamido-2-deoxy-β-<scp>D</scp>-glucopyranosyl)-2-deoxy-<scp>D</scp>-glucopyranose (N,n′-diacetylchitobiose) and 2-acetamido-6-O-(2-acetamido-2-deoxy-β-<scp>D</scp>-glucopyranosyl)-2-deoxy-<scp>D</scp>-glucopyranose

Abstract

During transfer of the N-acetyl-β-D-glucosaminyl (2-acetamido-2-deoxy-β-D-glucopyranosyl) residue from p-nitrophenyl N-acetyl-β-D-glucosaminide (p-nitrophenyl N-2-deoxy-β-D-glucopyranoside) on to N-acetyl-D-glucosamine (2-acetamido-2-deoxy-D-glucopyranose) catalysed by the N-acetylhexosaminidase from Aspergillus oryzae, the major isomer formed was found to depend on the time course of the reaction, 1 → 4 transfer predominating while the p-nitrophenyl glycoside was available as donor, but 1 → 6 transfer when the initially-formed 1 → 4 product took over as donor, results that could be interpreted in terms of a constant regioselectivity modulated by selective hydrolysis of the products.