SYNTHESIS OF ARYL 3-O-BETA-CELLOBIOSYL-BETA-D-GLUCOPYRANOSIDES FOR REACTIVITY STUDIES OF 1,3-1,4-BETA-GLUCANASES

A series of substituted aryl beta-glycosides derived from 3-O-beta-cel lobiosyl-D-glucopyranose with different phenol-leaving group abilities as measured by the pK(a) of the free phenol group upon enzymatic hydr olysis has been synthesised. Aryl beta-glycosides with a pK(a) of the free phenol leaving group > 5 were prepared by phase-transfer glycosid ation of the per-O-acetylated alpha-glycosyl bromide with the correspo nding phenol, whereas the 2,4-dinitrophenyl beta-glycoside was obtaine d by condensation of 1-fluoro-2,4-dinitrobenzene with the partially ac etylated trisaccharide followed by acid de-O-acetylation. The aryl bet a-glycosides have been used for reactivity studies of the wild-type Ba cillus licheniformis 1,3-1,4-beta-D-glucan 4-glucanohydrolase. The Ham mett plot log k(cat) versus pK(a) is biphasic with an upward curvature at low pK(a) values suggesting a change in transition-state structure depending on the aglycon. (C) 1998 Elsevier Science Ltd. All rights r eserved.