Metabolic studies with model cytochrome p-450 systems

Chloroquine-iron(III) tetra-arylporphyrin interactions and their effect on chloroquine oxidations catalyzed by iron(III) tetra-arylporphyrins

This paper reports a UV-Vis spectroscopic study on the interactions of chloroquine with anionic, cationic and neutral tetra-arylporphyrins and their iron(III) complexes in aqueous buffer and in methanolic solution. This study reveals that in water at pH 6.4 cooperative ion-pair and π-π interactions lead to complex formation between the anionic porphyrin species and chloroquine. In methanolic solution no π-π complexation is observed. The neutral and cationic porphyrins and metalloporphyrins do not form complexes with chloroquine. On the basis of these results, the iron(III) porphyrins have been used as catalysts for the oxidation of chloroquine by iodosylbenzene. The main oxidation product in all systems is monodesethylchloroquine. The anionic iron(III) porphyrins are the most active catalysts; in aqueous solution they are selective for oxidative deethylation whereas in methanol they also give five other oxidation products. The cationic and neutral iron(III) porphyrins are poor or inactive catalysts for chloroquine oxidation by iodosylbenzene. The effect of iron(III) porphyrin/chloroquine interactions on the yields and selectivity of the oxidation is discussed.