Biomimetic models of cytochbome P-450 monooxygenases: studies on cyclohexene oxygenation in metalloporphyrin-sodium borohydride-microcrystalline cellulose-oxygen systems

Abstract A new chemical model of cytochrome P-450 monooxygenases was established to investigate the mechanism of activation of molecular oxygen and subsequent oxygenation of substrate by cytochrome P-450. The system consists of metalloporphyrin (M(TPP)) and sodium borohydride (NaBH 4 ) in the presence of various types of promoters in the benzene solvent-catalyzed oxygenation of cyclohexene, resulting in five oxygenation products, viz . cyclohexene oxide, cyclohexenol, cyclohexenone, cyclohexanone and cyclohexanol. The effects of the following factors in the reaction were studied: (1) crown ethers, (2) reducing agent, (3) influence of promoters, (4) central metal ion in the Me(TPP) as a catalyst and (5) active oxygen scavengers. These results were compared with those of certain biological systems such as isolated rat hepatocytes and rat liver microsomes. Involvement of the hydroxyl radical in oxygenation in the model was suggested, whereas that of singlet oxygen was partially indicated in the biological system. From these results, the Mn(TPP)/NaBH 4 /Avicel® (microcrystalline form of cellulose)/O 2 system was found to be a good model of cytochrome P-450.