Fig. 1

Modular cascade biocatalysis for synthesis of (R/S)-HMTBA from l-Met. a The modular and combinatorial synthesis of (R/S)-HMTBA by the proposed modular cascade biocatalysis platform. Three general basic enzyme modules: Basic Module: l-amino acid deaminase (l-AAD) or l-amino acid oxidase (l-AAO) for deamination of l-Met to KMTB; Extender Module 1: R-specific dehydrogenase and formate dehydrogenase (FDH) for asymmetric reduction of KMTB to (R)-HMTBA; Extender Module 2: S-specific dehydrogenase and formate dehydrogenase (FDH) for asymmetric reduction of KMTB to (S)-HMTBA. b The artificially designed cascade biocatalysis protocol. Cascade 1: modular assembly for (R)-HMTBA synthesis via cascade BM with EM1. Cascade 2: modular assembly for (S)-HMTBA synthesis via cascade BM with EM2