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Engineered nonheme iron enzymes perform enantioselective radical azidation on aryl N -fluoroamide substrates. 

Mononuclear non-heme iron enzymes are a large class of enzymes catalyzing a wide-range of reactions. In this work, we report that a non-heme iron enzyme in Methyloversatilis thermotolerans , OvoA Mtht, has two different activities, as a thiol oxygenase and a sulfoxide synthase. When cysteine is presented as the only substrate, OvoA Mtht is a thiol oxygenase. In the presence of both histidine and cysteine as substrates, OvoA Mtht catalyzes the oxidative coupling between histidine and cysteine (a sulfoxide synthase). Additionally, we demonstrate that both substrates and the active site iron's secondary coordination shell residues exert exquisite control over the dual activities of OvoA Mtht (sulfoxide synthase vs. thiol oxygenase activities). OvoA Mtht is an excellent system for future detailed mechanistic investigation on how metal ligands and secondary coordination shell residues fine-tune the iron-center electronic properties to achieve different reactivities. 

Mononuclear nonheme iron(II) and 2‐oxoglutarate (Fe/2OG)‐dependent oxygenases and halogenases are known to catalyze a diverse set of oxidative reactions, including hydroxylation, halogenation, epoxidation, and desaturation in primary metabolism and natural product maturation. However, their use in abiotic transformations has mainly been limited to C−H oxidation. Herein, we show that various enzymes of this family, when reconstituted with Fe(II) or Fe(III), can catalyze Mukaiyama hydration—a redox neutral transformation. Distinct from the native reactions of the Fe/2OG enzymes, wherein oxygen atom transfer (OAT) catalyzed by an iron‐oxo species is involved, this nonnative transformation proceeds through a hydrogen atom transfer (HAT) pathway in a 2OG‐independent manner. Additionally, in contrast to conventional inorganic catalysts, wherein a dinuclear iron species is responsible for HAT, the Fe/2OG enzymes exploit a mononuclear iron center to support this reaction. Collectively, our work demonstrates that Fe/2OG enzymes have utility in catalysis beyond the current scope of catalytic oxidation.

 

Mononuclear nonheme iron(II) and 2‐oxoglutarate (Fe/2OG)‐dependent oxygenases and halogenases are known to catalyze a diverse set of oxidative reactions, including hydroxylation, halogenation, epoxidation, and desaturation in primary metabolism and natural product maturation. However, their use in abiotic transformations has mainly been limited to C−H oxidation. Herein, we show that various enzymes of this family, when reconstituted with Fe(II) or Fe(III), can catalyze Mukaiyama hydration—a redox neutral transformation. Distinct from the native reactions of the Fe/2OG enzymes, wherein oxygen atom transfer (OAT) catalyzed by an iron‐oxo species is involved, this nonnative transformation proceeds through a hydrogen atom transfer (HAT) pathway in a 2OG‐independent manner. Additionally, in contrast to conventional inorganic catalysts, wherein a dinuclear iron species is responsible for HAT, the Fe/2OG enzymes exploit a mononuclear iron center to support this reaction. Collectively, our work demonstrates that Fe/2OG enzymes have utility in catalysis beyond the current scope of catalytic oxidation.

 

Ergothioneine (ESH) and ovothiol A (OSHA) are two natural thiol‐histidine derivatives. ESH has been implicated as a longevity vitamin and OSHA inhibits the proliferation of hepatocarcinoma. The key biosynthetic step of ESH and OSHA in the aerobic pathways is the O₂‐dependent C−S bond formation catalyzed by non‐heme iron enzymes (e.g., OvoA in ovothiol biosynthesis), but due to the lack of identification of key reactive intermediate the mechanism of this novel reaction is unresolved. In this study, we report the identification and characterization of a kinetically competentS=1 iron(IV) intermediate supported by a four‐histidine ligand environment (three from the protein residues and one from the substrate) in enabling C−S bond formation in OvoA fromMethyloversatilis thermotoleran, which represents the first experimentally observed intermediate spin iron(IV) species in non‐heme iron enzymes. Results reported in this study thus set the stage to further dissect the mechanism of enzymatic oxidative C−S bond formation in the OSHA biosynthesis pathway. They also afford new opportunities to study the structure‐function relationship of high‐valent iron intermediates supported by a histidine rich ligand environment.

 

Ergothioneine (ESH) and ovothiol A (OSHA) are two natural thiol‐histidine derivatives. ESH has been implicated as a longevity vitamin and OSHA inhibits the proliferation of hepatocarcinoma. The key biosynthetic step of ESH and OSHA in the aerobic pathways is the O₂‐dependent C−S bond formation catalyzed by non‐heme iron enzymes (e.g., OvoA in ovothiol biosynthesis), but due to the lack of identification of key reactive intermediate the mechanism of this novel reaction is unresolved. In this study, we report the identification and characterization of a kinetically competentS=1 iron(IV) intermediate supported by a four‐histidine ligand environment (three from the protein residues and one from the substrate) in enabling C−S bond formation in OvoA fromMethyloversatilis thermotoleran, which represents the first experimentally observed intermediate spin iron(IV) species in non‐heme iron enzymes. Results reported in this study thus set the stage to further dissect the mechanism of enzymatic oxidative C−S bond formation in the OSHA biosynthesis pathway. They also afford new opportunities to study the structure‐function relationship of high‐valent iron intermediates supported by a histidine rich ligand environment.