To PLP or Not to PLP: Stereodivergent Transaminase-Catalyzed Reactions Directed by Kinetic and Thermodynamic Control

Selective catalysis is a key objective in organic synthesis, and reactions with differing kinetic and thermodynamic products present the opportunity for divergent reaction outcomes with a single catalyst. We report a biocatalytic method in which a single transaminase can form either <i>cis</i> or <i>trans</i> cyclohexylamines in high diastereoselectivity. With the model substrate 4-methylcyclohexanone, <i>E. coli</i> cells expressing WT-<i>Vf</i>-ATA form either diastereomer of the amine product in >10:1 dr and >70% conversion, depending on reaction conditions, stereodivergence that also extends to a range of substrates. In the case of α(2)-substituted ketones, a concurrent dynamic kinetic resolution enables conversion of racemic ketones into <i>cis</i> or <i>trans</i> amines that are enantiomerically and diastereomerically enriched. Supplementation (or not) of the PLP cofactor in the reaction was found to be key in directing the stereochemical outcome and informed the development of a modified preparation of cells expressing the transaminases that included a metabolic precursor to the PLP cofactor, resulting in cells with more holo ATA catalyst and higher catalytic activity. This research demonstrates a rare, but operationally simple, example of highly stereodivergent reactions effected by a single catalyst and sheds new light on the PLP cofactor as a handle to optimize biocatalysis by transaminases.