Alternative Synthesis of Cefamandole with Biocatalytic Acylation Catalyzed by Immobilized Cephalosporin-Acid Synthetase

Abstract

The processes of the biocatalytic acylation of 1-methyl-5-mercapto-1,2,3,4-tetrazolil-7-amino-cephalosporanic acid (7-TMCA) and 7-aminocephalosporanic acid (7-ACA) by methyl ester of mandelic acid (MEMA) were optimized with an immobilized cephalosporin-acid synthetase as the biocatalyst. Under optimized conditions in water-organic medium containing 43% (vol/vol) of ethylene glycol at 30°С with a spontaneous pH gradient in the range of 8.0–6.0, the following yields of biocatalytic transformations were reached: (80.8 ± 1.9)% for 7‑TMCA acylation (at a concentration of 100–120 mМ) resulted in cefamandole (CFM) production, and (88.6 ± 2.0)% for 7-ACA acylation of (at concentration of 140–170 mМ) resulted in a semiproduct of CFM (S-p CFM) formation. In the second process, the concentration of the target β-lactam product in the final reaction mixture is one and a half times higher than that with the first one. In light of the undoubted environmental benefits of the chemical transformation of S-p CFM to CFM over the process of the chemical production of 7-TMCA from 7-ACA, we conclude that the second pathway of combined chemical and biocatalytic CFM synthesis is preferable.

Enzymatic synthesis of cefazolin using immobilized recombinant cephalosporin-acid synthetase as the biocatalyst

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.

[Recombinant cephalosporin-acid synthesase: optimisation of expression in E.coli cells, immobilisation and application for biocatalytic cefazolin synthesis]

Cephalosporin acid synthetase (CASA) is responsible for specific to synthesis of cephalosporin-acids, its expression in Escherichia coli cells is accompanied by accumulation of unprocessed insoluble precursor. In order to optimize conditions of recombinant CASA production we have studied the effects of several parameters of strain cultivation, including growth media composition, temperature, and inoculation dose. Also plasmids for production of CASA variants with the signal sequence of Erwinia carotovora L-asparaginase (ansCASA) and "leaderless" CASA were created in search of more efficient expression constructs. Removal of the N-terminal secretion signal sequence reduced the production of functionally active CASA more than 10-fold and inhibited strain growth. Insertion of the L-asparaginase signal sequence increased the specific enzyme activity in the resultant recombinant strain. The ansCASA producing strain was used to develop the method of immobilization of the recombinant enzyme on an epoxy-activated macroporous acrylic support. The resultant biocatalyst performed effective synthesis of cefazolin from 3-[(5-methyl-1,3,4-thiadiazol-2-il)-thiomethyl]-7- aminocephalosporanic acid (MMTD-7-ACA) and methyl ester of 1(H)-tetrazolilacetic acid (МETzAA), under mild conditions a transformation level of MMTD-7-ACA to cefazolin of 95% is reached.