Biomimetic Oxidation Catalysis by Iron(III) Deuterophorphyrin Carrying a Deca-L-Alanine Peptide Chain

The deuterohemin complex carrying a deca-L-alanine peptide residue covalently linked to one of the propionic acid side chain of the porphyrin has been synthesized and its catalytic behaviour in biomimetic oxidations has been investigated by kinetic measurements. In the catalytic oxidation of a series of para-substituted thioanisoles by hydrogen peroxide a correlation has been found between the reaction rates and the Hammettσp parameter suggesting that a direct oxygen transfer from an iron-oxo species to the substrate sulfur atom takes place. This trend is similar to that found for chloroperoxidase whereas for normal peroxidases the rate of oxidation of the same substrates correlates with Hammett σ+ values. The catalytic oxidation of L- and D-tyrosine by hydrogen peroxide exhibit substrate saturation kinetics mimicking the enzymic reactions catalyzed by peroxidases. The reaction shows stereoselective effects, the oxidation of D-tyrosine being favoured with respect to that of the L isomer.