Mechanistic Studies Of Oxidations Catalyzed By Model Systems Derived From Cytochrome P450

Cytochrome P450s are one of the most important oxidases in the living creatures. Because it is capable to catalyze a variety of oxidations, it has been extensively focused for some decades. During the recent30years, many synthetic metalloporphyrins derived from P450s have been synthesized, characterized and used to approach the behaviors of P450s and deeply understand the mechanism of it. At first, this paper reviewed the mechanistic studies and discoveries of the active intermediate of oxidations catalyzed by cytochrome P450s and its derived model systems. The research contents of this paper can be divided into two parts:(1) In chapter2of this paper, a metalloporphyrin-soluble iodosylarene system was established. By employing free radical trapping reaction of2,4,6-tri-tert-butylphenol and epoxidation reaction of c/s-stilbene as templated reactions, plus the UV-vis spectroscopy and ESI-MS analysis, we performed kinetic and mechanistic studies of this system. Kinetic data indicated that the formation of (por)Mnv=O species was the rate-determining step in the free radical trapping reation, so it was able to observe the accumulation of the metalloporphyrin-soluble iodosylarene adduct. However, the rate-determining step was changed to the oxygen atom transfer from (por)Mnv=O species to olefin in the epoxidation reaction, so it was able to observe the accumulation of (por)Mnv=O species. In addition, UV-vis spectroscopies of the reaction between metalloporphyrin and soluble iodosylarene in the absence of reductant clearly revealed the transformation from metalloporphyrin-soluble iodosylarene adduct to (por)Mnv=O species. According to the evidences of kinetic data, UV-vis spectroscopy and ESI-MS analysis, we expanded the "shunt pathway" and proved that metalloporphyrin-soluble iodosylarene adduct was the key precursor of the formation of (por)Mnv=O when iodosylbenzene derivatives were used as oxidants.(2) In chapter3of this paper, a metalloporphyrin-NaClO2system was established. By employing the hydroxylation of alkanes and epoxidation of olefins as templated reactions, plus the UV-vis spectroscopies and free radical trapping reaction studies, the metalloporphyrin-NaClO2system was compared to that of NaClO system. This paper found that high valent metal-oxo intermediate could not be formed under our experimental conditions and the mechanism of oxidations involved in metalloporphyrin-NaClO2system was very distinct when other terminal oxidants were used. In addition, this paper also found that the formation of adduct existed between the reaction of metalloporphyrin and olefin, which would lead to competition of the formation of active species. According to UV-vis spectroscopies and kinetic studies, a novel mechanism involving a metal-chlorite species as active intermediate was proposed.