Biocatalytic synthesis of β-hydroxy tryptophan regioisomers

We report a biocatalytic strategy to access novel β-hydroxy L-tryptophan regioisomers using an L-threonine transaldolase. We show that classical threonine aldolases cannot perform this transformation, highlighting the unique reactivity of transaldolases. By coupling turnover to byproduct removal, high isolated yields of up to 90% were achieved. This reaction enables a multi-enzyme cascade to synthesize diverse non-canonical analogs of L-tryptophan.