An Engineered Tryptophan Synthase Opens New Enzymatic Pathways to ß-Methyltryptophan and Derivatives.

ABSTRACT

ß-Methyltryptophans (ß-mTrp) are precursors in the biosynthesis of bioactive natural products and are used in the synthesis of peptidomimetic-based therapeutics. Currently ß-mTrp is produced by inefficient multistep synthetic methods. Here we demonstrate how an engineered variant of tryptophan synthase from Salmonella (StTrpS) can catalyse the efficient condensation of l-threonine and various indoles to generate ß-mTrp and derivatives in a single step. Although l-serine is the natural substrate for TrpS, targeted mutagenesis of the StTrpS active site provided a variant (ßL166V) that can better accommodate l-Thr as a substrate. The condensation of l-Thr and indole proceeds with retention of configuration at both α- and ß-positions to give (2S,3S)-ß-mTrp. The integration of StTrpS (ßL166V) with l-amino acid oxidase, halogenase enzymes and palladium chemocatalysts provides access to further d-configured and regioselectively halogenated or arylated ß-mTrp derivatives.