Thermodynamics and Kinetic Aspects Involved in the Enzymatic Resolution of (R,S)-3-Fluoroalanine in a Coupled System of Redox Reactions Catalyzed by Dehydrogenases

• Published in: Organic process research & development 2006-05, Vol.10 (3), p.673-677
• Main Authors: Gonçalves, Luciana P. B, Antunes, O. A. C, Oestreicher, Enrique G
• Format: Article
• Language: English
• ISSN: 1083-6160; 1520-586X
• DOI: 10.1021/op060027o

Two systems of redox enzymatic reactions were tested, looking forward to the preparation of (S)-3-fluoroalanine, a potent antibiotic, by kinetic resolution of rac-3-fluoroalanine. This starting material was the main substrate for the deaminative oxidation reaction catalyzed by l-alanine dehydrogenase (l-AlaDH) in the presence of NAD+. One system was formed by coupling this reaction (main reaction) to the reduction of 3-fluoropyruvate (a cascade system) produced in the main reaction catalyzed by l-lactate dehydrogenase (l-LDH) in the presence of NADH, also formed in the main reaction. This system, that was able to achieve 92% of conversion, allows the accumulation of NH4 +, one of the secondary products of the main reaction. The other coupled redox system involved the coupling to the l-AlaDH reaction to the aminative reduction reaction of α-ketoglutarate in the presence of NADH and NH4 + (both side products of the main reaction) catalyzed by l-glutamate dehydrogenase (l-GluDH), that allows accumulation of 3-fluoropyruvate. With this system, the extent of the reaction in the coupled system was only 22%. This big difference in the efficiency of both systems was identified as being the result of a different potency of the products that accumulates in both systems, acting as inhibitors of l-AlaDH. It was demonstrated that 3-fluoropyruvate is a much stronger inhibitor of l-AlaDH than NH4 +. This fact, and not thermodynamic considerations, explains the results obtained with both systems.