Abstract
The oxidation of certain 2-alkyl-3-hydroxynaphtho-1,4-quinones, pyrimidines and nucleosides by hydrogen peroxide, catalysed by 5,10,15,20-tetrakis(pentafluorophenyl)porphine iron(ni) chloride is investigated. This catalyst is particularly efficient in the oxidation of the hydroxynaphthoquinones; a proposed epoxide product which was not isolated reacts further to give low yields of a dehydro dimer and an oxoindane carboxylate, which are fully characterised. The mechanisms of formation of these secondary products from the primary epoxide product are discussed. Oxidation of certain pyrimidines and nucleosides using the same catalyst-oxidant combination proceeds in low yield to give unisolatable products, or none at all. Thus, the catalyst-oxidant system is suitable in certain cases as a biomimetic method for the preparation of larger amounts of material to complement in vivo studies of drug metabolism. Kinetic analysis by the initial rates method of the oxidation of hydroxynaphthoquinones using this system is consistent with rapid reaction of the organic substrate with an oxoperferryl intermediate formed in the first and rate-limiting step. In the absence of organic substrate, hydrogen peroxide oxidises the catalyst to a oxoferryl species, probably via the oxoperferryl species. This oxoferryl compound is itself bleached by hydrogen peroxide, probably via oxidation of the porphyrin ring.