Enzyme-catalysed partial deacylation of 1,6-anhydro-2,3,4-tri-O-butyryl-β-D-glucopyranose in the presence of methanol

Abstract

Lipase ex pancreas (EC 3.1.1.3), lipase ex wheat-germ (EC 3.1.1.3), and chymotrypsin (EC 3.4.4.5) are compared in their power to catalyse deacylation of 1,6-anhydro-2,3,4-tri-O-butyryl-β-D-glucopyranose. The action of the three enzymes has been found locoselective. In the use of a hydrolase the selectivity of the reaction was affected by composition of the reaction mixture. Lipase ex porcine pancreas in a solution containing 20% of methanol (v/v) catalysed deacylation preferentially from C-2, but on raising the methanol concentration to 50% (v/v) deacylation from C-4 prevailed over that from C-2. Analogously, at the lower methanol concentration deacylation effected by wheat-germ lipase occurred to a greater extent on C-2, whereas at the higher concentration on C-3. With chymotrypsin ex hog pancreas at the lower concentration of methanol the prevailing deacylation was on C-4, at the higher on C-3. Compared to a chemically catalysed hydrolysis, whether by methanolic hydrogen chloride or hydrazine hydrate, the locoselectivity of an enzyme-catalysed deacylation of 1,6-anhydro-2,3,4-tri-O-butyryl-β-D-glucopyranose is substantially higher.