A Concise Enzyme Cascade for the Synthesis of Enantiopure Levosalbutamol

Cascade biocatalysis is attractive for the synthesis of chiral chemicals and pharmaceuticals because it streamlines traditional multi-step synthesis by eliminating intermediate workup and (de)protection steps. However, many enzyme cascades are designed for the chiral intermediates (requiring further chemical elaboration) instead of final enantiopure APIs. Here, we developed a concise enzyme cascade for the synthesis of enantiopure ( R )-levosalbutamol, a β 2 -adrenergic agonist used to treat bronchospasm. Two key enzymes, xylB and CgKR1, were subjected to structure-guided semi-rational engineering and computational design using NAC4ED and EVOLVEpro, resulting in 29- and 420-fold enhancements in activity, respectively. Mechanistic studies revealed improvements in substrate binding, active site geometry, and conformational dynamics. Implementation of an optimized two-cell one-pot process enabled the production of levosalbutamol with 98% conversion, 87% yield and >99% ee. This work demonstrates the great potential of integrating advanced enzyme engineering with cascade catalysis for the efficient synthesis of enantiopure pharmaceuticals.