Electroenzymatic synthesis of (S)-styrene oxide employing zinc oxide/carbon black composite electrode

(S)-styrene oxide, a useful chiral intermediate, has been synthesized using an electroenzymatic method with direct electrochemical FADH₂ regeneration. Low electroenzymatic efficiency arising from the fast FADH₂ reoxidation could be overcome by employing a zinc oxide/carbon black composite electrode. The attractive interaction between zinc oxide and styrene monooxygenase kept the local enzyme concentration high near the electrode surface, thereby increasing the accessibility of FADH₂ from the electrode surface to the enzyme. By adjusting the reaction conditions such as oxygen solubility, a high electroenzymatic efficiency of 65% was obtained. As a result, the reaction rate was increased while the amount of the side-products from the cofactor reoxidation process was decreased. The metal oxide/carbon black composite electrode can be efficiently used for electroenzymatic syntheses using diffusible-flavin dependent monooxygenases.