One-Pot Biocatalytic Synthesis of Substituted d-Tryptophans from Indoles Enabled by an Engineered Aminotransferase

d-Tryptophan and its derivatives are important precursors of a wide range of indole-containing pharmaceuticals and natural products. Here, we developed a one-pot biocatalytic process enabling the synthesis of d-tryptophans from indoles in good yields and high enantiomeric excess (91% to >99%). Our method couples the synthesis of l-tryptophans catalyzed by Salmonella enterica tryptophan synthase with a stereoinversion cascade mediated by Proteus myxofaciens l-amino acid deaminase and an aminotransferase variant that we engineered to display native-like activity toward d-tryptophan. Our process is applicable to preparative-scale synthesis of a broad range of d-tryptophan derivatives containing electron-donating or -withdrawing substituents at all benzene-ring positions on the indole group.