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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, thereby 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 hemoproteins derived from a bacterial cytochrome P450 that efficiently catalyze α-carbonyl alkylation of isomeric silyl enol ethers, producing stereopure products. Through screening and directed evolution, we generated P450BM3 variant P411-SCA-5188, which catalyzes 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. 

In nature and synthetic chemistry, stereoselective [2+1] cyclopropanation is the most prevalent strategy for the synthesis of chiral cyclopropanes, a class of key pharmacophores in pharmaceuticals and bioactive natural products. One of the most extensively studied reactions in the organic chemist’s arsenal, stereoselective [2+1] cyclopropanation, largely relies on the use of stereodefined olefins, which can require elaborate laboratory synthesis or tedious separation to ensure high stereoselectivity. Here we report engineered hemoproteins derived from a bacterial cytochrome P450 that catalyze the synthesis of chiral 1,2,3-polysubstituted cyclopropanes, regardless of the stereopurity of the olefin substrates used. Cytochrome P450BM3 variant P411-INC-5185 exclusively converts (Z)-enol acetates to enantio- and diastereoenriched cyclopropanes and in the model reaction delivers a leftover (E)-enol acetate with 98% stereopurity, using whole Escherichia coli cells. P411-INC-5185 was further engineered with a single mutation to enable the biotransformation of (E)-enol acetates to α-branched ketones with high levels of enantioselectivity while simultaneously catalyzing the cyclopropanation of (Z)-enol acetates with excellent activities and selectivities. We conducted docking studies and molecular dynamics simulations to understand how active-site residues distinguish between the substrate isomers and enable the enzyme to perform these distinct transformations with such high selectivities. Computational studies suggest the observed enantio- and diastereoselectivities are achieved through a stepwise pathway. These biotransformations streamline the synthesis of chiral 1,2,3-polysubstituted cyclopropanes from readily available mixtures of (Z/E)-olefins, adding a new dimension to classical cyclopropanation methods.