Natural prostaglandins (PG) F-2 alpha and E-1 as well as (+)-cloprostenol were regioselectively Il-acylated using Novozym(R) 435 as a catalyst and vinyl acetate as an acyl donor. Unlike the above compounds the 15-OH group of PGE(2) was also acylated with a significant velocity under the same conditions. The enantiospecificity of the lipase-catalysed 11-acetylation of cloprostenol was established by separate treatment of (+)- and (-)-cloprostenols. (C) 1999 Elsevier Science Ltd. All rights reserved.