Upgraded Bioelectrocatalytic N₂ Fixation: From N₂ to Chiral Amine Intermediates

Abstract

Enantiomerically pure chiral amines are of increasing value in the preparation of bioactive compounds, pharmaceuticals, and agrochemicals. ω-Transaminase (ω-TA) is an ideal catalyst for asymmetric amination because of its excellent enantioselectivity and wide substrate scope. To shift the equilibrium of reactions catalyzed by ω-TA to the side of the amine product, an upgraded N2 fixation system based on bioelectrocatalysis was developed to realize the conversion from N2 to chiral amine intermediates. The produced NH3 was in situ reacted with l-alanine dehydrogenase to generate alanine with NADH as a coenzyme. ω-TA transferred the amino group from alanine to ketone substrates and finally produced the desired chiral amine intermediates. The cathode of the upgraded N2 fixation system supplied enough reducing power to synchronously realize the regeneration of reduced methyl viologen (MV•+) and NADH for the nitrogenase and l-alanine dehydrogenase. The coproduct, pyruvate, was consumed by l-alanine dehydrogenase to regenerate alanine and push the equilibrium to the side of amine. After 10 h of reaction, the concentration of 1-methyl-3-phenylpropylamine achieved 0.54 mM with the 27.6% highest faradaic efficiency and >99% enantiomeric excess (eep). Because of the wide substrate scope and excellent enantioselectivity of ω-TA, the upgraded N2 fixation system has great potential to produce a variety of chiral amine intermediates for pharmaceuticals and other applications.

Natural and Engineered Electron Transfer of Nitrogenase

“…To this end, the Minteer group has extended the use of reduced MV in bioelectrosynthetic cells to reduce NADH. In this way, the NH 3 formed by nitrogenase can be upgraded to further products of interest, such as chiral amines and chiral amino acids [155,156].…”

Recent Enzymatic Electrochemistry for Reductive Reactions

“…Recent research has also capitalized on electrocatalytic N 2 fixation with the Fe and MoFe proteins, although the produced NH 3 is further upgraded in a cascade that employs a total of five enzymes: Fe protein, MoFe protein, diaphorase, L‐alanine dehydrogenase and ω‐transaminase (Figure ). In this way, the Minteer group demonstrated that chiral amines (such as (R)‐1‐methyl‐3‐phenylpropylamine) could be produced where reduced MV was used to fix N 2 with nitrogenase as well as to produce reduced nicotinamide adenine dinucleotide (NADH), required for L‐alanine dehydrogenase . This concept was recently upgraded further to a system in which a H 2 ase‐based H 2 ‐oxidizing anode was coupled to a nitrogenase‐based cathode for N 2 reduction to NH 3 (dependent on ATP hydrolysis); the produced NH 3 was subsequently coupled with diaphorase and leucine dehydrogenase to perform asymmetric α‐keto acid aminations forming chiral amino acids with high FEs and enantiomeric excess .…”

Recent Progress in Applications of Enzymatic Bioelectrocatalysis

“…There are mainly two types of bioelectrosynthetic systems: a fuel-cell-type [142,[144][145][146][147][148][149] and an electrolysis-type [28,53,141,143,[150][151][152][153][154]. The former realizes a spontaneous production of compounds without any external power supplies, whereas the latter proceeds relatively rapid reactions due to an optimally controlled electrode potential to realize diffusion-controlled conditions.…”

“…On the other hand, reductive production of chiral compounds is useful in many cases. Minteer's group reported various NAD + -dependent multienzymatic cascade reactions for generating chiral compounds, as shown in Figure 5 [149,152,153].…”