Invited Talk 21st International Conference on Biological Inorganic Chemistry 2025

Reconstituted Hemoprotein as an Artificial Metalloenzyme Catalyzing Olefin Cyclopropanation (122117)

Koji Oohora 1
  1. The University of Osaka, Suita, OSAKA, Japan

Hemoprotein containing heme, an iron porphyrin, as a cofactor is a promising scaffold toward artificial metalloenzymes due to the unique characteristics derived from the synergetic combination of the metal cofactor and protein matrix. In this context, our group has demonstrated artificial metalloenzymes constructed by insertion of an artificial metal cofactor into the heme-binding site of a simple hemoprotein [1].

These engineered proteins show catalytic activities including C–H bond hydroxylation, C–H bond amination, and olefin cyclopropanation. In the case of olefin cyclopropanation, redox potential of metal center is critical for both of formation and activation of the active species. A porphycene iron complex as a cofactor largely accelerates the formation of the metal carbenoid species in a protein matrix and shows 26-fold times higher turnover frequency for styrene substrate [2]. Recently, we found that an iron complex of electron deficient porphyrin in a protein matrix demonstrates catalytic cyclopropanation of octene as a more inert alkane [3]. In this work, we hypothesized that investigation using myoglobins reconstituted with synthetic cofactors possessing various redox potentials reveals the correlation of redox potential and cyclopropanation reactivity. We employed iron porphyrin with two and one trifluoromethyl groups at peripheral sites (FePor(CF3)2 and FePorCF3, respectively), native heme and iron porphycene (FePc) as cofactors. The range of Fe(II)/Fe(III) redox potentials of the four myoglobins exceeds 340 mV. It was found that myoglobin with more positive redox potential shows higher reactivity toward inert alkenes. In particular, myoglobin reconstituted with FePor(CF3)2(rMb(FePor(CF3)2)) exhibits a 165-fold higher turnover number for 1-octene cyclopropanation compared to native myoglobin. Mechanistic studies indicate that rMb(FePor(CF3)2) generates an active species with a radical character. In contrast, myoglobin reconstituted with FePc provides a detectable iron–carbene species [2] with an electrophilic character. This work highlights the significance of redox-focused design of the iron porphyrinoid cofactor in hemoproteins to enhance cyclopropanation reactivity.

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  1. [1] K. Oohora K., T. Hayashi, Dalton Trans., 2021, 50, 1940-1949.
  2. [2] K. Oohora, H. Meichin, L. Zhao, M. W. Wolf, A. Nakayama, J. Hasegawa, N. Lehnert, T. Hayashi, J. Am. Chem. Soc., 2017, 139, 17265-17268.
  3. [3] Y. Kagawa, K. Oohora, T. Himiyama, A. Suzuki, T. Hayashi, Angew. Chem. Int. Ed., 2024, 63, e202403485.