- Directed Evolution of a Cytochrome P450 Carbene Transferase for Selective Functionalization of Cyclic Compounds
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Transfers of carbene moieties to heterocycles or cyclic alkenes to obtain C(sp2)-H alkylation or cyclopropane products are valuable transformations for synthesis of pharmacophores and chemical building blocks. Through their readily tunable active-site geometries, hemoprotein "carbene transferases" could provide an alternative to traditional transition metal catalysts by enabling heterocycle functionalizations with high chemo-, regio-, and stereocontrol. However, carbene transferases accepting heterocyclic substrates are scarce; the few enzymes capable of heterocycle or cyclic internal alkene functionalization described to date are characterized by low turnovers or depend on artificially introduced, costly iridium-porphyrin cofactors. We addressed this challenge by evolving a cytochrome P450 for highly efficient carbene transfer to indoles, pyrroles, and cyclic alkenes. We first developed a spectrophotometric high-throughput screening assay based on 1-methylindole C3-alkylation that enabled rapid analysis of thousands of P450 variants and comprehensive directed evolution via random and targeted mutagenesis. This effort yielded a P450 variant with 11 amino acid substitutions and a large deletion of the non-catalytic P450 reductase domain, which chemoselectively C3-alkylates indoles with up to 470 turnovers per minute and 18000 total turnovers. We subsequently used this optimized alkylation variant for parallel evolution toward more challenging heterocycle carbene functionalizations, including C2/C3 regioselective pyrrole alkylation, enantioselective indole alkylation with ethyl 2-diazopropanoate, and cyclic internal alkene cyclopropanation. The resulting set of efficient biocatalysts showcases the tunability of hemoproteins for highly selective functionalization of cyclic targets and the power of directed evolution to enhance the scope of new-to-nature enzyme catalysts.
- Brandenberg, Oliver F.,Chen, Kai,Arnold, Frances H.
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- Myoglobin-Catalyzed C?H Functionalization of Unprotected Indoles
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Functionalized indoles are recurrent motifs in bioactive natural products and pharmaceuticals. While transition metal-catalyzed carbene transfer has provided an attractive route to afford C3-functionalized indoles, these protocols are viable only in the presence of N-protected indoles, owing to competition from the more facile N?H insertion reaction. Herein, a biocatalytic strategy for enabling the direct C?H functionalization of unprotected indoles is reported. Engineered variants of myoglobin provide efficient biocatalysts for this reaction, which has no precedents in the biological world, enabling the transformation of a broad range of indoles in the presence of ethyl α-diazoacetate to give the corresponding C3-functionalized derivatives in high conversion yields and excellent chemoselectivity. This strategy could be exploited to develop a concise chemoenzymatic route to afford the nonsteroidal anti-inflammatory drug indomethacin.
- Vargas, David A.,Tinoco, Antonio,Tyagi, Vikas,Fasan, Rudi
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- Halogenated indole-3-acetic acids as oxidatively activated prodrugs with potential for targeted cancer therapy
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Substituted indole-3-acetic acid (IAA) derivatives, plant auxins with potential for use as prodrugs in enzyme-prodrug directed cancer therapies, were oxidised with horseradish peroxidase (HRP) and toxicity against V79 Chinese hamster lung fibroblasts was determined. Rate constants for oxidation by HRP compound I were also measured. Halogenated IAAs were found to be the most cytotoxic, with typical surviving fractions of -3 after incubation for 2 h with 100 μM prodrug and HRP.
- Rossiter, Sharon,Folkes, Lisa K.,Wardman, Peter
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- Fe-catalyzed Fukuyama-type indole synthesis triggered by hydrogen atom transfer
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Fe, Co, and Mn hydride-initiated radical olefin additions have enjoyed great success in modern synthesis, yet the extension of other hydrogen radicalophiles instead of olefins remains largely elusive. Herein, we report an efficient Fe-catalyzed intramolec
- Huang, Hanmin,Yu, Min,Zhang, Tianze
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p. 10501 - 10505
(2021/08/20)
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