A novel d-mandelate dehydrogenase used in three-enzyme cascade reaction for highly efficient synthesis of non-natural chiral amino acids

• A novel D-mandelate dehydrogenase was discovered from Lactobacillus brevis.
• This LbDMDH displayed the highest catalytic efficiency as compared to values reported in literatures.
• As much as 0.2 M (30.4 g L−1) of rac-mandelate could be converted at 1-L scale into chiral L-phenylglycine with 96.4% conversion, giving a space-time yield of 50.4 g L−1 d−1.
• Five chiral L-phenylglycine derivatives were also prepared employing this newly developed cascade reaction.

A novel NAD+-dependent D-mandelate dehydrogenase was identified from Lactobacillus brevis (LbDMDH). After purified to homogeneity, the optimum pH and temperature for oxidation of D-mandelate were pH 10.0 and 40 °C, and the Km and kcat were 1.1 mM and 355 s−1 respectively. Employing the LbDMDH together with a mandelate racemase from Pseudomonas putida and a leucine dehydrogenase (EsLeuDH) from Exiguobacterium sibiricum, we established a three-step one-pot domino reaction system for preparing chiral L-phenylglycine from racemic mandelic acid with internal cofactor recycling. Under the optimum conditions, 30.4 g rac-mandelic acid (0.2 M) at 1 L scale had been converted into chiral L-phenylglycine, with 96.4% conversion, 86.5% isolation yield, >99% eep and 50.4 g L−1 d−1 space-time yield.

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