A new thioether-ligated iron porphyrin as a model of a protonated form of P450 active site

Thioether-ligated iron porphyrin (complex 1) was synthesized as a model of the protonated form of P450 to explore the possible involvement of the protonated form in the catalytic cycle, and ether-ligated iron porphyrin (complex 2) was also synthesized for comparison. The thioether and ether ligands enhanced heterolytic O-O bond cleavage of peroxy acid-iron porphyrin complex even in highly hydrophobic media without the assistance of acid or base, using mCPPAA as an oxidant. Competitive oxidation of cyclooctane/cyclooctene catalyzed by iron porphyrins showed that complexes 1 and 2 are less effective than heme thiolate (P450 and a synthetic heme thiolate (SR complex)) in oxidizing alkane. The possibility that thiol-ligated heme, which is a protonated form of heme thiolate, is not involved in the active intermediate structure of P450 is indicated by this result. This is the first report concerning the oxidizing ability of a thioether-ligated iron porphyrin.