Metalloporphyrins cofactor

The observation that iron porphyrins can catalyze, under mild conditions, epoxidations of alkenes when iodosylbenzene is used as the oxidant has been followed up by a number of studies on metallopor-phyrins as models for cytochrome P-4S0 enzymes. Cytochrome P-4S0 enzymes catalyze epoxidation of alkenes by molecular oxygen in the presence of a hydrogen donor, NAOPH cofactor. This has led to the study of a number of systems based on a metalloporphyrin/02/reducing agent, to bring about epoxidation of alkenes. 

Their properties can be further improved based on the coordination chemistry strategy for supramolecular systems (31, 38, 39, 46, 56, 116, 191, 262-265). For example, one can exploit the electron donor-acceptor and/or ET properties of the ancillary complexes or make use of them as cofactors, creating new pathways for the oxidation of organic substrate (183, 266, 267). In particular, transition metal complexes connected to the periphery of we.so-pyridylporphyrins (268, 269) can modify the stereochemical environment or even modulate the electronic characteristics of the metalloporphyrin center. This aspect was explored in the case of the Mn(4-TRPyP) and Mn(3-TRPyP) systems, because of their contrasting stereochemistry (Fig. 27). 

The studies on these Hangman porphyrins and other macrocyclic Hangman platforms [205] clearly demonstrate that exceptional catalysis may be achieved when redox and PT properties of a cofactor are controlled independently. A key requirement is that the PT distance is kept short, which may be accomplished by orthogonalizing ET and PT coordinates. The benefits of incorporating PT functionality into redox catalysis can only be realized when a suitable geometry is established. Moreover, the Hangman platforms show that a multifunctional activity of a single metalloporphyrin-based scaffold is achieved by the addition of proton control to a redox platform. This observation is evocative of natural heme-de-pendent proteins that employ a conserved protoporphyrin IX cofactor to affect a myriad of chemical reactivities. 

Antibodies that bind to metallopoiphyrins provide an ideal cofactor in oxidation reactions, similar to cytochrome P-450 catalyzed oxidations. The metalloporphyrins provides the chemical activation site where the antibody exerts its selectivity (25), This antibody-mediated metalloporphyrin chemistry adds another dimension to the use of antibody catalysts in organic syntheses. Research on these systems has demonstrated that antibody technology represents a powerful and versatile tool for creating tailored biocatalysts. Research and development in this area should continue to generate efficient and robust catalysts with high specificity particularly for organic syntheses. 

---