Regioselective galloylation of methyl β-d-glucopyranoside by a lipase

Chromogenic substrate 4-nitrophenyl gallate was prepared in four steps and used for selection of hydrolases specific to gallic ester hydrolysis from among 22 commercial lipases, proteases, and crude glycanase cocktails. Enzymes displaying galloyl esterase activity were tested in regioselective galloylation of methyl beta-d-glucopyranoside with vinyl gallate. Lipozyme TL IM in acetonitrile was found to afford the highest conversion (37 %). The reaction proceeded with strict regioselectivity toward the primary hydroxyl of the glucopyranoside ring, giving in preparative scale 27 % of purified methyl 6-O-galloyl-beta-d-glucopyranoside as a sole product.