Exploiting nature’s catalysts for non-natural transformations that are inaccessible to chemocatalysis is highly desirable but challenging. On the one hand, the widespread nicotinamide-dependent oxidoreductases have not been utilized for single-electron-transfer-induced bimolecular cross-couplings; on the other, the addition of catalytic asymmetric radical conjugate to terminal alkenes remains a challenge owing to strong racemic background reaction and unselective termination of prochiral radical species. Here we report a chemomimetic biocatalysitic approach for construction of alpha-carbonyl stereocentres via an unnatural intermolecular conjugate addition of N-(acyloxy)phthalimides-derived radicals with acceptor-substituted terminal alkenes, by combination of visible-light excitation and nicotinamide-dependent ketoreductases (KREDs). Based on protein crystal structure, we engineered KREDs via a semi-rational mutagenesis strategy to improve reaction outcomes with a small and high-quality variants library. Mechanistic investigations combining wet experiments, crystallographic studies and computational simulations demonstrate that the repurposed biocatalyst can suppress racemic background reaction and unselected side reactions, yielding enantioselectivity that is challenging to achieve by chemocatalysis.
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Data relating to the materials and methods, experimental procedures, mechanistic studies and computational calculations, HPLC spectra and NMR spectra are available in the Supplementary Information. The atomic coordinates of the optimized computational models are available in the Supplementary Data. The configurations of molecular dynamics simulations have been deposited in GitHub (https://github.com/fpikachu96/KRED-data). The atomic coordinates of apo-P2-D12, apo-K3, P2-D12-2a, K3-2a and K3-NHPI have been deposited in the Protein Data Bank (http://www.rcsb.org) under accession code 7VDO, 7VE7, 7EJJ, 7EJI and 7EJH, respectively. All other data are available from the authors upon reasonable request.
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This work was supported by the US Department of Energy (no. DE-SC0018420 to H.Z.), the National Natural Science Foundation of China (no. 2073077 to B.W.) and the National Key Research and Development Program of China (no. 2019YFA09005000 to J.Z.). NMR data were collected at the Carl R. Woese Institute for Genomic Biology Core, on a 600-MHz NMR funded by NIH grant no. S10-RR028833 (to H.Z.). We thank Codexis, Inc. for kindly sharing the amino acid sequence information of KRED-P2-D12, the staff of beamlines BL17U1 and BL19U1 of the Shanghai Synchrotron Radiation Facility and the National Center for Protein Science Shanghai for access and help with X-ray data collection.
The authors declare no competing interests.
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Huang, X., Feng, J., Cui, J. et al. Photoinduced chemomimetic biocatalysis for enantioselective intermolecular radical conjugate addition. Nat Catal 5, 586–593 (2022). https://doi.org/10.1038/s41929-022-00777-4
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