Abstract
Amine dehydrogenase (AmDH) possesses tremendous potential for the synthesis of chiral amines because AmDH catalyzes the asymmetric reductive amination of ketone with high enatioselectivity. Although a reductive application of AmDH is favored in practice, the oxidative route is interesting as well for the preparation of chiral amines. Here, the kinetic resolution of racemic amines using AmDH was first extensively studied, and the AmDH reaction was combined with an NADH oxidase (Nox) to regenerate NAD+ and to drive the reaction forward. When the kinetic resolution was carried out with 10 mM rac-2-aminoheptane and 5 mM rac-α-methylbenzylamine (α-MBA) using purified enzymes, the enantiomeric excess (ee) values were less than 26% due to the product inhibition of AmDH by ketone and the inhibition of Nox by the substrate amine. The use of a whole-cell biocatalyst co-expressing AmDH and Nox apparently reduces the substrate and product inhibition, and/or it increases the stability of the enzymes. Fifty millimoles (50 mM) rac-2-aminoheptane and 20 mM rac-α-MBA were successfully resolved into the (S)-form with >99% ee using whole cells. The present study demonstrates the potential of a whole-cell biocatalyst co-expressing AmDH and Nox for the kinetic resolution of racemic amines.
Highlights
Considerable efforts have been made to economically obtain enantiomerically pure intermediates for drugs and agrochemicals
We describe the production of (S)-amines through the oxidative deamination of racemic amines by amine dehydrogenase (AmDH) with help of an NADH oxidase (Nox) (Figure 1)
The plasmid was introduced into E. coli (BL21) cells and the transformants were grown at 37 ◦ C in 1 L LB-containing kanamycin
Summary
Considerable efforts have been made to economically obtain enantiomerically pure intermediates for drugs and agrochemicals. The chiral amines are of great interest to the pharmaceutical and fine-chemical industries, since enantiopure amines are important building blocks for pharmaceutical manufacturing [1]. Given the significance of chiral amines, their efficient synthesis in enantiopure form has become an attractive challenge to organic chemists and biologists in recent years [2,3,4]. Many biocatalytic methods for the production of chiral amines have been developed using biocatalysts, such as lipase [5], amine oxidase [6], imine reductase [7], transaminase [8], ammonia lyases [9], Pictet-Spenglerase [10], barberine bridge enzyme [11], engineered. Each enzyme has its own advantages and disadvantages for the synthesis of chiral amines ([13] and references therein for more details).
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