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Enzyme-controlled stereoselective radical cyclization to arenes enabled by metalloredox biocatalysis

Nature Catalysis volume 6, pages 628–636 (2023)Cite this article

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Abstract

The effective induction of high levels of stereocontrol for free-radical-mediated transformations represents a notorious challenge in asymmetric catalysis. Herein, we describe a metalloredox biocatalysis strategy to repurpose natural cytochromes P450 to catalyse asymmetric radical cyclization to arenes through an unnatural electron transfer mechanism. Directed evolution afforded a series of engineered P450 aromatic radical cyclases with complementary selectivities: P450arc1 and P450arc2 facilitated enantioconvergent transformations of racemic substrates, giving rise to either enantiomer of the product with excellent total turnover numbers (up to 12,000). In addition to these enantioconvergent variants, another engineered radical cyclase, P450arc3, permitted efficient kinetic resolution of racemic chloride substrates (S factor = 18). Furthermore, computational studies revealed a proton-coupled electron transfer mechanism for the radical–polar crossover step, suggesting the potential role of the haem carboxylate as a base catalyst. Collectively, the excellent tunability of this metalloenzyme family provides an exciting platform for harnessing free radical intermediates for asymmetric catalysis.

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Fig. 1: A metalloenzyme platform for stereoselective radical cyclization.
Fig. 2: Discovery and engineering of enantioconvergent P450 radical cyclases.
Fig. 3: Substrate scope of P450arc-catalysed enantioconvergent radical cyclization.
Fig. 4: P450arc-catalysed stereoselective transformations of α-chloro substrate 3a.
Fig. 5: Time course of P450arc-catalysed enantioconvergent radical cyclization processes.
Fig. 6: Reaction energy profile of biocatalytic radical cyclization to arenes using a model system for serine-ligated P450arc.

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Data availability

All data are available in the main text and the Supplementary Information or available from the authors upon reasonable request. X-ray crystal structures of 2i and (R)-3a are available free of charge from the Cambridge Crystallographic Data Centre under reference numbers CCDC 2184585 and 2184586. Plasmids encoding P450arcs reported in this study are available for research purposes from Y.Y. under a material transfer agreement with the University of California Santa Barbara.

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Acknowledgements

This research is supported by the NIH (R35GM147387 to Y.Y. and R35GM128779 to P.L.) and the University of California Santa Barbara (Y.Y.). We acknowledge the BioPACIFIC MIP (NSF Materials Innovation Platform, DMR-1933487) and the NSF MRSEC Program (DMR-1720256) for access to instrumentation. DFT calculations were performed at the Center for Research Computing of the University of Pittsburgh and the Extreme Science and Engineering Discovery Environment supported by the National Science Foundation grant number ACI-1548562. Y.F. is an Andrew W. Mellon Predoctoral Fellow. We thank L. Zhang (University of California Santa Barbara) and Y. Wang (University of Pittsburgh) for critical reading of this manuscript.

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Authors and Affiliations

  1. Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA, USA

    Wenzhen Fu, Natalia M. Neris, Yunlong Zhao, Benjamin Krohn-Hansen & Yang Yang

  2. Department of Chemistry, University of Pittsburgh, Pittsburgh, PA, USA

    Yue Fu & Peng Liu

  3. Biomolecular Science and Engineering Program, University of California Santa Barbara, Santa Barbara, CA, USA

    Yang Yang

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  1. Wenzhen Fu
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Contributions

Y.Y. conceived and directed the project. W.F., N.M.N., Y.Z. and B.K.-H. designed and performed the experiments. Y.F. carried out the computational studies with P.L. providing guidance. Y.Y., Y.F. and P.L. wrote the manuscript with the input of all other authors.

Corresponding authors

Correspondence to Peng Liu or Yang Yang.

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Competing interests

Y.Y., W.F., N.M.N. and Y.Z. are inventors on a patent application (US provisional patent no. 63/477,081) submitted by the University of California Santa Barbara that covers stereoselective biocatalytic radical addition to arenes. The remaining authors declare no competing interests.

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Nature Catalysis thanks Gonzalo Jiménez-Osé and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Methods, Tables 1–15, Figs. 1–26, Notes 1–12, Discussion and References.

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Supplementary Data 1

Crystallographic data for compound 2i.

Supplementary Data 2

Crystallographic data for compound 3a.

Supplementary Data 3

Atomic coordinates of the optimized computational models from molecular dynamics simulations.

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Fu, W., Neris, N.M., Fu, Y. et al. Enzyme-controlled stereoselective radical cyclization to arenes enabled by metalloredox biocatalysis. Nat Catal 6, 628–636 (2023). https://doi.org/10.1038/s41929-023-00986-5

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