Reprogramming the Catalytic Pocket of Baeyer–Villiger Monooxygenase for Environmentally Compatible Synthesis of a Chiral Sulfoxide Pharmaceutical

Proton pump inhibitors such as ( R )-lansoprazole are essential for gastric disease treatment, yet conventional syntheses rely on environmentally hazardous transition metal catalysts. Here, we reprogrammed a Baeyer–Villiger monooxygenase from Cupriavidus basilensis ( Cb BVMO) to enable environmentally compatible synthesis of ( R )-lansoprazole from lansoprazole sulfide. By a four-amino-acid scanning strategy, a total of four variants from three residue sites exhibiting a >3-fold increase in specific activity were identified. Among them, a single mutant L315Y achieved a 15-fold increase in the specific activity. Computational studies revealed that L315Y stabilizes the catalytic transition state via π–π interactions with R312, resulting in the reduction of activation energy. Subsequent combinatorial mutagenesis yielded optimized variant Cb BVMO V3 with an over 30-fold increase in activity, reaching 11.6 U/mg. Following process optimization, this variant exhibited strong catalytic performance in a 4 L-scale biotransformation, achieving 97% conversion of lansoprazole sulfide (50 g/L) within 8 h. This biocatalytic route reduces the environmental factor from 62.6 to 4.75 kg waste /kg product and lowers the production cost by 80% compared to the chemical method. By eliminating toxic metal catalysts and minimizing waste generation, our work adds further evidence that engineered BVMOs are environmentally benign alternatives for synthesizing chiral sulfoxide pharmaceuticals.