Asymmetric Epoxidation and Sulfoxidation Catalyzed by a New Styrene Monooxygenase from Bradyrhizobium

Asymmetric epoxidation catalyzed with styrene monooxygenase (SMO) is a powerful enzymatic process producing enantiopure styrene epoxide derivatives. To establish a more diversified reservoir of SMOs, a new SMO from Bradyrhizobium sp. ORS 375, named Br SMO, was mined from the database and characterized. Br SMO was constituted of an epoxygenase component of 415 amino acid residues and an NADH-dependent flavin reductase component of 175 residues. Br SMO catalyzed the epoxidation of styrene and 7 more styrene derivatives, yielding the corresponding ( S )-epoxides with excellent enantiomeric excesses (95– > 99% ee), with the highest activity achieved for styrene. Br SMO also catalyzed the asymmetric sulfoxidation of 7 sulfides, producing the corresponding ( R )-sulfoxides (20–90% ee) with good yields.