Biosynthesis of Diverse Ephedra-Type Alkaloids via a Newly Identified Enzymatic Cascade

Ephedra-type alkaloids represent a large class of natural and synthetic phenylpropanolamine molecules with great pharmaceutical values. However, the existing methods typically rely on chemical approaches to diversify the N-group modification of Ephedra-type alkaloids. Herein, we report a 2-step enzymatic assembly line for creating structurally diverse Ephedra-type alkaloids to replace the conventional chemical modification steps. We first identified a new carboligase from Bacillus subtilis (BsAlsS, acetolactate synthase) as a robust catalyst to yield different phenylacetylcarbinol (PAC) analogs from diverse aromatic aldehydes with near 100% conversions. Subsequently, we screened imine reductases (IREDs) for the reductive amination of PAC analogs. It was found that IRG02 from Streptomyces albidoflavus had good activities with conversions ranging from 37% to 84% for the reductive alkylamination with diverse amine partners such as allylamine, propargylamine, and cyclopropylamine. Overall, 3 new bio-modifications at the N-group of Ephedra-type alkaloids were established. Taken together, our work lays a foundation for the future implementation of biocatalysis for synthesizing structurally diverse Ephedra-type alkaloids with potential new pharmaceutical applications.