Biocatalytic cascade conversion of racemic amines into optically pure ones using enantiocomplementary ω-transaminases (ω-TAs) has been developed by thermodynamic and kinetic control of reaction pathways where 12 competing reactions occur with pyruvate and isopropylamine used as cosubstrates. Thermodynamic control was achieved under reduced pressure for selective removal of a coproduct (i.e., acetone), leading to elimination of six undesirable reactions. Engineered orthogonality in substrate specificities of ω-TAs was exploited for kinetic control, enabling suppression of four additional reactions. Taken together, the net reaction pathway could be directed to two desired reactions (i.e., oxidative deamination of R-amine and reductive amination of the resulting ketone into antipode S-amine). This strategy afforded one-pot deracemization of various chiral amines with >99% eeS and 85-99% reaction yields of the resulting S-amine products. The in vitro cascade reaction could be successfully implemented in a live microbe using glucose or l-threonine as a cheap amino acceptor precursor, demonstrating a synthetic metabolic pathway enabling deracemization of chiral amines which has never been observed in living organisms.
Bibliographical noteFunding Information:
This work was funded by the National Research Foundation of Korea under the Basic Science Research Program (2016R1A2B4008470). S.-W.H. was financially supported by Initiative for Biological Function & Systems under the BK21 PLUS program of Korean Ministry of Education. We are grateful to the technical work of Saerom Park and Joonhyun Song.
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