Regioselective acylation of polyhydroxylated natural compounds catalyzed by Candida antarctica lipase B (Novozym 435) in organic solvents

A systematic investigation on the transesterification activity and regioselectivity of the immobilized lipase B from Candida antarctica (Novozym 435) has been performed. This enzyme has been found to be quite active in such solvents as THF, acetone, dioxane, and in mixtures of these solvents with pyridine. Several glycopyranosides have been acetylated, showing that the regioselectivity displayed by Novozym 435 towards sugar secondary OH's is deeply influenced by the nature of the aglycone and by the stereochemistry of the glycosidic bond. This information on the regioselectivity of the lipase has been exploited for the preparation of acetyl derivatives of flavonoid glycosides.