Facile in vitro biocatalytic production of diverse tryptamines

: Tryptamines are a medicinally important class of small molecules that serve as precursors to more complex, clinically used indole alkaloid natural products. Typically, tryptamine analogues are prepared from indoles through multistep synthetic routes. In the natural world, the desirable tryptamine synthon is produced in a single step by l-tryptophan decarboxylases (TDCs). However, no TDCs are known to combine high activity and substrate promiscuity, which might enable a practical biocatalytic route to tryptamine analogues. We have now identified the TDC from Ruminococcus gnavus as the first highly active and promiscuous member of this enzyme family. RgnTDC performs up to 96 000 turnovers and readily accommodates tryptophan analogues with substituents at the 4, 5, 6, and 7 positions, as well as alternative heterocycles, thus enabling the facile biocatalytic synthesis of >20 tryptamine analogues. We demonstrate the utility of this enzyme in a two-step biocatalytic sequence with an engineered tryptophan synthase to afford an efficient, cost-effective route to tryptamines from commercially available indole starting materials.