From Hemoabzymes to Hemozymes: The Long but Fascinating Story of the Elaboration of New Biocatalysts for Selective Oxidation Reactions

The design of artificial hemoproteins that could lead to new biocatalysts for selective oxidation reactions constitutes a really promising challenge for a wide range of industrial applications. The main objective stands in the generation of new artificial materials that are able to work under a wide range of conditions and to use clean oxidants such as O₂ or H₂O₂, which fits the current concept of “green chemistry” in a global context of “sustainable growth”. In vivo, such reactions are performed by a wide class of heme-thiolate proteins, cytochromes P450, that catalyze the oxidation of drugs at their heme-active site, using dioxygen as oxidant, in the presence of electrons delivered from NADPH by cytochrome P450 reductase. Several strategies were used to design new artificial hemoproteins to mimic these enzymes, that associate a synthetic iron(III)-tetraarylporphyrin, to mimic the heme of P450s, to a protein that is supposed to mimic the apoprotein of P450s, and thus, that is supposed to selectively position the substrate with respect to the iron atom and to induce a selectivity in the catalyzed reaction.

A first generation of artificial hemoproteins or “Hemoabzymes”, was obtained by the non-covalent association of a synthetic Fe(III)-a₃b-tetra-o-carboxyphenylporphyrin (FeToCPP) or of a microperoxidase 8 (MP8) with monoclonal antibodies raised against these cofactors. The later MP8-antibody complexes were shown to catalyze the regio-selective nitration of phenol derivatives by H₂O₂/NO₂ and the stereo-selective oxidation of organic compounds such as sulphides by H₂O₂.

A second generation of artificial hemoproteins or “Hemozymes”, was obtained by the non-covalent association of a non-relevant protein with a tetraarylporphyrin. Several strategies were used, the most successful of which, named “host-guest” strategy involved the non-covalent incorporation of water-soluble anionic iron-porphyrins into xylanase A from Streptomyces Lividans, that was low-cost, available in large quantities, and, in addition, heat-resistant. The artificial hemoproteins obtained were found able to perform efficiently the stereoselective oxidation of organic compounds such as sulphides and alkenes by H₂O₂ and KHSO₅.

New strategies aiming at using dioxygen as an oxidant, are currently investigated.

References

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