Substantially enhancing enzymatic regioselective acylation of 1-β-d-arabinofuranosylcytosine with vinyl caprylate by using a co-solvent mixture of hexane and pyridine

Abstract

Novozym 435-catalyzed regioselective acylation of 1- β - d -arabinofuranosylcytosine (ara-C) with vinyl caprylate for the preparation of its 5′- O -acyl derivative has been performed in six co-solvent mixtures and three pure polar solvents for the first time. Novozym 435 displayed low activity towards 1- β - d -arabinofuranosylcytosine in pure polar solvents, although those solvents can dissolve the nucleosides well. When a hexane–pyridine co-solvent system was adopted, both the initial rate and the substrate conversion were enhanced markedly. The most suitable co-solvent, initial water activity, reaction temperature and the molar ratio of vinyl caprylate to ara-C were hexane/pyridine (28/72, v/v), 0.03, 40 °C and 15, respectively. Under these conditions, the initial rate, the substrate conversion and the regioselectivity were as high as 99.0 mmol h −1 , 98% and >99%, respectively. The product of the Novozym 435-catalyzed reaction was characterized by 13 C NMR and confirmed to be 5′- O -octanoyl 1- β - d -arabinofuranosylcytosine.