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Published November 2, 2023 | in press
Journal Article Open

Biocatalytic, stereoconvergent alkylation of (Z/E)-trisubstituted silyl enol ethers

Abstract

The selective conversion of mixtures of Z/E alkenes into chiral products is a synthetic challenge. Biocatalytic strategies can transform isomeric alkenes into stereopure compounds, but enzymes typically convert only one alkene isomer, limiting the overall yield. Additional strategies have been used to interconvert alkene isomers, often at the cost of increasing energy consumption and chemical waste. Here we present engineered haemoproteins derived from a bacterial cytochrome P450 that efficiently catalyse α-carbonyl alkylation of isomeric silyl enol ethers, producing stereopure products. Through screening and directed evolution, we generated P450_(BM3) variant P411-SCA-5188, which catalyses stereoconvergent carbene transfer in Escherichia coli with high efficiency and stereoselectivity to various Z/E mixtures of silyl enol ethers. In contrast to established stereospecific transformations that leave one isomer unreacted, P411-SCA-5188 converts both isomers to a stereopure product. This biocatalytic approach simplifies the synthesis of chiral α-branched ketones by eliminating the need for stoichiometric chiral auxiliaries, strongly basic alkali-metal enolates and harsh conditions, delivering products with high efficiency and excellent chemo- and stereoselectivities.

Copyright and License

© The Author(s), under exclusive licence to Springer Nature Limited 2023.

Acknowledgement

Support by the National Science Foundation Division of Molecular and Cellular Biosciences (MCB-2016137 to F.H.A.) is gratefully acknowledged. R.M. acknowledges support from the Swiss National Science Foundation (SNSF) Early Mobility Postdoctoral Fellowship (P2ELP2_195118). D.J.W. acknowledges support from the National Science Foundation Graduate Research Fellowship (DGE-1745301). K.M.S. acknowledges support from NIH Ruth L. Kirschstein National Research Service Award (1F32GM145123-01A1). Support by the National Science Foundation Division of Chemistry (CHE-2153972 to K.N.H.) and the Alexander von Humboldt Foundation (Feodor Lynen Fellowship, T.R.) is gratefully acknowledged. We thank S. C. Virgil for the maintenance of the Caltech Center for Catalysis and Chemical Synthesis (3CS). We thank M. Shahgoli for mass spectrometry assistance. We thank D. VanderVelde for the maintenance of the Caltech NMR facility. We also thank S. Brinkmann-Chen for the helpful discussions and comments on the manuscript. Calculations were performed on the Hoffman2 cluster at the University of California, Los Angeles.

Contributions

R.M. conceptualized and designed the overall project under the guidance of F.H.A. R.M. and D.J.W. conducted the initial screening of haem proteins. D.M.T. performed the directed evolution experiments, with support from S.J.W. R.M. and D.J.W. investigated the substrate scope and reaction mechanism. K.M.S. purified and obtained both (Z)-1a and (E)-1a. T.R. carried out the computational studies with K.N.H. providing guidance. R.M. and F.H.A. wrote the manuscript with input from all authors.

Data Availability

The original materials and data that support the findings of this study are available within the paper and its Supplementary Information.

Conflict of Interest

The authors declare no competing interests.

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Additional details

Created:
November 9, 2023
Modified:
January 9, 2024