Photosensitized NAD(P)H regeneration systems; application in the reduction of butan-2-one, pyruvic, and acetoacetic acids and in the reductive amination of pyruvic and oxoglutaric acid to amino acid

Abstract

The photosensitized formation of NAD(P)H by enzyme-catalysed processes has been accomplished. With Ru(bpy)²⁺ ₃ as sensitizer, methyl viologen, MV²⁺ as primary electron acceptor, and (NH₄)₃EDTA or 2-mercaptoethanol, NADPH is formed in the presence of ferredoxin NADP⁺-reductase as enzyme catalyst. Zinc(II) meso-tetramethylpyridiniumporphyrin, ZnTMPyP⁴⁺ is used as sensitizer for the photoinduced production of NADH using the same components and lipoamide dehydrogenase as enzyme catalyst. The photoinduced NAD(P)H regeneration systems have been coupled to secondary enzyme-catalysed processes such as the reduction of butan-2-one to butan-2-ol, pyruvic acid to lactic acid, acetoacetic acid to β-hydroxybutyric acid, as well as to the reductive amination of pyruvic acid to alanine and of α-oxoglutaric acid to glutamic acid. The products exhibit high optical purity and the enzymes and the coenzymes show high turnover numbers and stability.