KINETIC CONTROL OF REGIOSELECTIVITY IN GLYCOSIDASE-CATALYZED DISACCHARIDE SYNTHESIS - PREPARATION OF 2-ACETAMIDO-4-O-(2-ACETAMIDO-2-DEOXY-BETA-D-GLUCOPYRANOSYL)-2-DEOXY-D-GLUCOPYRANOSE (N,N'-DIACETYLCHITOBIOSE) AND 2-ACETAMIDO-6-O-(2-ACETAMIDO-2-DEOXY-BETA-D-GLUCOPYRANOSYL)-2-DEOXY-D-GLUCOPYRANOSE

During transfer of the N-acetyl-D-glucosaminyl (2-acetamido-2-deoxy-beta-D-glucopyranosyl) residue from p-nitrophenyl N-acetyl-beta-D-glucosaminide (p-nitrophenyl N-2-acetamido-2-deoxy-beta-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