Enzymatic synthesis of cephalothin from 7-aminocephalosporanic acid (7-ACA) and amide derivatives of 2-thienylacetic acid (2-TA) using penicillin G acylase (pen G acylase) was studied. Two amide derivatives of 2-TA namely 2-thienylacetamide (2-TAA) and 2-thienylacetohydroxamic acid (2-TAH) were used in this study. The main reason for choosing amide but not the methyl ester derivative of 2-TA for the enzymatic synthesis was to increase their. solubilities in water. The solubility of 2-TA methyl ester (2-TAM), 2-TAA, and 2-TAH in aqueous solution is 8 +/-0.05 mM, 87 +/- 0.75 mM and 120 +/- 1.65 mM, respectively. Enzymatic conversion of 2-TAH to cephalothin yielded side products bur they were nor found in the conversion of 2-TAA to cephalothin. The side products were derived from reactions between hydroxyamine and 7-ACA. The effects of pH, temperature, initial substrate concentrations and reaction time on the conversion of 2-TAA and 7-ACA to cephalothin were examined. The optimum reaction condition was determined at pH 0.5 and 10 similar to 15 degrees C The best conversion yield of 72% was obtained when the initial concentration of 2-TAA and 7-ACA was at 0.4 M and 0.1 M, respectively. Furthermore. a one-step method was developed to purify cephalothin from the enzymatic reaction mixture with the: purity of 91% and the recovery yield of 96%. (C) 2000 Elsevier Science Inc. All rights reserved.