CAL-B-catalyzed synthesis of different 5'-O-monoester derivatives of 6-azauridine via a one-step highly regioselective enzymatic acylation route was successfully performed for the first time. The effects of some crucial factors on the enzymatic undec-10-enoylation of 6-azauridine were examined. The optimal reaction medium, molar ratio of 6-azauridine to vinyl undec-10-enoate and reaction temperature were found to be anhydrous acetone, 1:3 and 50 degrees C, under which the reaction I-ate, the substrate conversion and the regioselectivity were 22.3 mM/h, 99.0% and 99.0%, respectively. In addition, the enzyme recognition of acyl donors was investigated. The results showed that the enzyme activity varied widely with different acyl donors owing to the specific structure of the lipase active site and the acyl donors. 5'-O-Monoesters of 6-azauridine were achieved exclusively with all the acyl donors tested. (C) 2009 American Institute of Chemical Engineers Biotechnol. Prog., 25: 784-791, 2009