Enzymatic Asymmetric Synthesis of Enantiomerically Pure Aliphatic, Aromatic and Arylaliphatic Amines with (R)-Selective Amine Transaminases

Seven (R)-selective amine transaminases (R-ATAs) recently discovered by an in silico-based approach in sequence databases were produced recombinantly in Escherichia coli and subjected to partial purification by ammonium sulfate precipitation. A range of additives and various buffers were investigated to identify best conditions to ensure good storage stability and stable activity during biocatalysis. All enzymes show pH optima between pH 7.5-9. These R-ATAs were then applied in the asymmetric synthesis of twelve aliphatic, aromatic and arylaliphatic (R)-amines starting from the corresponding prochiral ketones using a lactate dehydrogenase/glucose dehydrogenase system to shift the equilibrium. For all ketones, at least one enzyme was found that allows complete conversion to the corresponding chiral amine having excellent optical purities > 99% ee. Variations in substrate profiles are also discussed based on the phylogenetic relationships between the seven R-ATAs. Thus, we have identified a versatile toolbox of (R)-amine transaminases showing remarkable properties for application in biocatalysis.