A method for the synthesis of β-lactam antibiotic cefazolin (CEZ) by enzymatic acylation of 7-amino-3-(5-methyl-l,3,4-thiadiazol-2-yl)thiomethyl-3-cephem-4-carboxylic acid (TDA) using immobilized cephalosporin-acid synthetase (IECASA) from recombinant E. coli strain VKPM B-12316 has been developed. A stepwise pH gradient designed on the basis of investigations on the solubility of components was applied for synthesis. This helped in avoiding the precipitation of TDA in the reaction when its initial concentration was high (150-200 mM). Thus, under optimal conditions a high yield of CEZ (relative to TDA) of 92-95% was obtained. Where the final reaction mixture contained 65-85 mg/mL of CEZ, 4-5 mg/mL of unreacted TDA, and 40-60 mg/mL of the by-product, 1(H)-tetrazolylacetic acid (TzAA). Testing of optimized CEZ synthesis using IECASA in a batch reactor has proved sufficiently high operational stability of the biocatalyst, with its residual activity after the 25th cycle accounting for about 83 ± 2% of its starting value. The half-inactivation period of IECASA was estimated as 85 cycles of CEZ synthesis.
Keywords: Cefazolin; Cephalosporin acid synthetase; Enzymatic synthesis; Immobilized enzyme; Solubility.