Dehydrogenase-Catalyzed Oxidation of Furanics: Exploitation of Hemoglobin Catalytic Promiscuity.

The catalytic promiscuity of hemoglobin (Hb) was explored for regenerating oxidized nicotinamide cofactors [NAD(P) ]. With H O as oxidant, Hb efficiently oxidized NAD(P)H into NAD(P) within 30 min. The new NAD(P) regeneration system was coupled with horse liver alcohol dehydrogenase (HLADH) for the oxidation of bio-based furanics such as furfural and 5-hydroxymethylfurfural (HMF). The target acids (e.g., 2,5-furandicarboxylic acid, FDCA) were prepared with moderate-to-good yields. The enzymatic regeneration method was applied in l-glutamic dehydrogenase (DH)-mediated oxidative deamination of lglutamate and for l-lactic-DH-mediated oxidation of l-lactate, which furnished α-ketoglutarate and pyruvate in yields of 97 % and 81 %, respectively. A total turnover number (TTON) of up to approximately 5000 for cofactor and an E factor of less than 110 were obtained in the bi-enzymatic cascade synthesis of α-ketoglutarate. Overall, a proof-of-concept based on catalytic promiscuity of Hb was provided for in situ regeneration of NAD(P) in DH-catalyzed oxidation reactions.