Glycolipid Enzyme Model. XI. Search for Active Sites of Glycolipids as Hydrolase Model

Synthesized glycolipids have been reported as hydrolase models, and their active sites could be explained on the basis of 2, 3-hydroxyl groups of the sugar moiety. In this study, a glycolipid was found to exhibit acidic nature in water, reflecting the dissociation of the hydroxyl group, and the conjugated base to be concerned with the hydrolysing activity. The 2- or 3-deoxy-glycolipids then were synthesized and used in the hydrolysis of phenylalanine p-nitrophenyl ester. 3-Deoxy-glycolipid showed only a little lower hydrolysing activity than the perfect glycolipid, while 2-deoxy-glycolipid, considerably lower activity. The hydroxyl group on 2-position is thus shown to be a predominant active site, although 3-hydroxyl one also is a weaker active site. That is, the oxy anion on 2-position of a sugar moiety is esti-mated as active species that attack the carbonyl carbon of an ester nucleophilically with consequent bond cleavage.