Coupled Immobilized Amine Dehydrogenase and Glucose Dehydrogenase for Asymmetric Synthesis of Amines by Reductive Amination with Cofactor Recycling

The amine dehydrogenase (AmDH) engineered from the phenylalanine dehydrogenase of Rhodococcus sp. M4 was directly immobilized on magnetic nanoparticles (MNP) from the cell-free extract containing his-tagged AmDH through affinity attachment to give AmDH-MNPs with high yield, enzyme loading efficiency, and specific enzyme loading. AmDH-MNPs showed higher activity and productivity than the free enzyme for the asymmetric reductive amination of 4-phenyl-2-butanone 1a and phenylacetone 1b, producing the corresponding amines (R)-2a,b in 99% ee and 99% yield, and with recycling of NADH for up to 3956times. AmDH-MNPs were easily recycled, retaining 91% of the original productivity in the third cycle of the reductive amination of 1a. Coupling of immobilized AmDH and immobilized glucose dehydrogenase (GDH) for the asymmetric reductive amination of 1a gave (R)-2a in 99% ee and 74% yield, with a total turnover number (TTN) of 2940 for NADH recycling. Both immobilized enzymes showed good recyclability, retaining 81% productivity in the third reaction cycle. The developed method with coupled immobilized AmDH and immobilized GDH for the asymmetric reductive amination of ketones is useful for the synthesis of enantiopure amines, superior to the use of coupled isolated enzymes with enhanced catalytic performance and reduced enzyme cost through catalyst recycling.