A USEFUL AND VERSATILE PROCEDURE FOR THE ACYLATION OF NUCLEOSIDES THROUGH AN ENZYMATIC-REACTION

Lipase-mediated acylation of nucleosides with oxime esters in organic solvents has been achieved. Candida antarctica lipases (SP435 and SP435A) showed high regioselectivity toward the primary hydroxyl group of both deoxy- and ribonucleosides, whereas other lipases exhibited poor results for this goal. 2'-Deoxynucleosides, such as thymidine and 2'-deoxyadenosine, were acylated with oxime esters carrying saturated, unsaturated, aromatic, and functionalized chains, giving 5'-O-acylated compounds together with small quantities of the 3'-O-acylated regioisomer. Uridine, adenosine, and inosine, as representative ribonucleosides, were acylated exclusively at the 5'-OH by using the same methodology. Nucleosides bearing a cytosine ring were found to be unreactive with oxime esters under the same conditions. 2'-Deoxycytidine was acylated with acid anhydrides and C. antarctica lipase to give N,5'-O-diacylated compounds, whereas cytidine gave mixtures, reason for which it had to be previously chemically N-acylated and then subjected to the oxime esters and lipase, giving the same results as ribonucleosides.