Chloroperoxidase-catalyzed epoxidation of styrene in aqueous and nonaqueous media

To overcome poor product yields and stability in aqueous solution, we have examined the chloroperoxidase (CPO from Caldariomyces fumago) catalyzed oxidation of styrene in organic media using tert-butyl hydroperoxide as external oxidant. CPO's intrinsic catalytic activity in tert-butanol, as reflected in its k_cat value, was ca. one-fourth of that in aqueous buffer, indicating that the enzyme remains highly active in the organic solvent. Styrene epoxidation reactions were modeled in both aqueous and nonaqueous media to provide global kinetic information, which dominates non-initial rate conditions and is heavily influenced by continuous deactivation of the CPO. Deactivation studies revealed that the enzyme is deactivated quickly by the combination of the tert-butyl hydroperoxide and styrene, possibly due to the styrenic free radicals generated during the enzymatic reaction. These results may enable catalyst-engineering strategies to be initiated to improve the prospects of using CPO in nonaqueous media for large-scale epoxidation reactions.