Bioinspired oxidation of oximes to nitric oxide with dioxygen by a nonheme iron(II) complex

Bhattacharya, S.; Lakshman, Triloke Ranjan; Sutradhar, Subhankar; Tiwari, Chandan Kumar; Paine, Tapan Kanti

doi:10.1007/s00775-019-01726-6

Cited by 4 publications

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“…In order to rigorously evaluate the mechanism of oxime oxidation by heme peroxo intermediates, we carried out the detailed characterization of (1) both organic and inorganic reaction products of bulk/large‐scale reactions; (2) the expected nitroxyl NO − reaction product using triphenylphosphine (PPh 3 ) as a sacrificial substrate; [50b] and (3) products of oxime oxidation where the reactants were isotopically labeled (i.e., either by 18 O or 15 N). In that, we purified and characterized the expected ketone products, 2 a – g (Scheme 3), resulting from scaled‐up reactions between [(TPP)Fe III (O 2 2− )] − and substrates, 1 a – g , via NMR ( 1 H and 13 C), FT‐IR, ESI‐MS, and LC–MS methodologies (Figures S10–S23).…”

Section: Resultsmentioning

confidence: 99%

“…To achieve this goal, the oxidation of substrate 1 e was carried out by [(TPP)Fe III (O 2 2− )] − in the presence of excess PPh 3 . When the final reaction mixture was analyzed by 31 P NMR (Figure S24), PPh 3 ( δ =−5.49 ppm) was observed to convert to both its oxide, O=PPh 3 ( δ =29.8 ppm), and the aza‐ylide, HN=PPh 3 ( δ =21.1 ppm), clearly implicating NO − as one of the products of oxime oxidation [50b, 62] . In further support, when 15 N‐labeled 1 e oxime substrate was used, the label was translocated into the aza‐ylide with high fidelity, shifting its mass from 278.10 to 279.10 m/z (Figure S25).…”

Section: Resultsmentioning

confidence: 99%

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The Role of Heme Peroxo Oxidants in the Rational Mechanistic Modeling of Nitric Oxide Synthase: Characterization of Key Intermediates and Elucidation of the Mechanism

et al. 2022

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Mammalian nitric oxide synthase (NOS) mediates the two‐step O2‐dependent oxidative degradation of arginine, and has been linked to a medley of disease situations in humans. Nonetheless, its exact mechanism of action still remains unclear. This work presents the first NOS model system where biologically proposed heme superoxo and peroxo intermediates are assessed as active oxidants against oxime substrates. Markedly, heme peroxo intermediates engaged in a bioinspired oxime oxidation reaction pathway, converting oximes to ketones and nitroxyl anions (NO−). Detailed thermodynamic, kinetic, and mechanistic interrogations all evince a rate‐limiting step primarily driven by the nucleophilicity of the heme peroxo moiety. Coherent with other findings, 18O and 15N isotope substitution experiments herein suffice compelling evidence toward a detailed mechanism, which draw close parallels to one of the enzymatic proposals. Intriguingly, recent enzymatic studies also lend credence to these findings, and several relevant reaction intermediates have been observed during NOS turnover.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

The Role of Heme Peroxo Oxidants in the Rational Mechanistic Modeling of Nitric Oxide Synthase: Characterization of Key Intermediates and Elucidation of the Mechanism

et al. 2022

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“…35 Furthermore, complex 2 oxidizes oximes to the corresponding ketones with the formation of HNO; the ketone product derives the oxygen atom (Scheme 6). 38…”

Section: Oxidation Of Substrates By O 2 -Derived Oxidantsmentioning

confidence: 99%

“…The 6-coordinate iron(II)−α-hydroxy acid complexes undergo four-electron oxidation to the corresponding iron(II)–carboxylate complexes. Following this work, the reactivity of O 2 -derived oxidants from different iron(II)−α-hydroxy acid complexes on polydentate ligand frameworks was explored in our group. − ,− Similar to the cofactors and substrates in enzymes, iron-coordinated α-hydroxy acids act as the bioinspired two-electron sacrificial reductant for the generation of reactive iron–oxygen oxidants. In exploring the dioxygen reduction by iron(II)−α-hydroxy acid complexes, a new mode of O 2 activation has been highlighted.…”

Section: Introductionmentioning

confidence: 99%

Dioxygen Reduction and Bioinspired Oxidations by Non-heme Iron(II)−α-Hydroxy Acid Complexes

Chatterjee,

Paine

2023

Acc. Chem. Res.

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Metrics & More Article Recommendations CONSPECTUS: Aerobic organisms involve dioxygen-activating iron enzymes to perform various metabolically relevant chemical transformations. Among these enzymes, mononuclear non-heme iron enzymes reductively activate dioxygen to catalyze diverse biological oxidations, including oxygenation of C−H and C�C bonds and C−C bond cleavage with amazing selectivity. Several non-heme enzymes utilize organic cofactors as electron sources for dioxygen reduction, leading to the generation of iron−oxygen intermediates that act as active oxidants in the catalytic cycle. These unique enzymatic reactions influence the design of small molecule synthetic compounds to emulate enzyme functions and to develop bioinspired catalysts for performing selective oxidation of organic substrates with dioxygen. Selective electron transfer during dioxygen reduction on iron centers of synthetic models by a sacrificial reductant requires appropriate design strategies. Taking lessons from the role of enzyme− cofactor complexes in the selective electron transfer process, our group utilized ternary iron(II)−α-hydroxy acid complexes supported by polydentate ligands for dioxygen reduction and bioinspired oxidations. This Account focuses on the role of coordinated sacrificial reductants in the selective electron transfer for dioxygen reduction by iron complexes and highlights the versatility of iron(II)−α-hydroxy acid complexes in affecting dioxygen-dependent oxidation/oxygenation reactions. The iron(II)coordinated α-hydroxy acid anions undergo two-electron oxidative decarboxylation concomitant with the generation of reactive iron−oxygen oxidants. A nucleophilic iron(II)−hydroperoxo species was intercepted in the decarboxylation pathway. In the presence of a Lewis acid, the O−O bond of the nucleophilic oxidant is heterolytically cleaved to generate an electrophilic iron(IV)− oxo-hydroxo oxidant. Most importantly, the oxidants generated with or without Lewis acid can carry out cis-dihydroxylation of alkenes. Furthermore, the electrophilic iron−oxygen oxidant selectively hydroxylates strong C−H bonds. Another electrophilic iron(IV)−oxo oxidant, generated from the iron(II)−α-hydroxy acid complexes in the presence of a protic acid, carries out C−H bond halogenation by using a halide anion. Thus, different metal−oxygen intermediates could be generated from dioxygen using a single reductant, and the reactivity of the ternary complexes can be tuned using external additives (Lewis/protic acid). The catalytic potential of the iron(II)−α-hydroxy complexes in performing O 2 -dependent oxygenations has been demonstrated. Different factors that govern the reactivity of iron−oxygen oxidants from ternary iron(II) complexes are presented. The versatile reactivity of the oxidants provides useful insights into developing catalytic methods for the selective incorporation of oxidized functionalities under environmentally benign conditions using aerial oxygen as the terminal oxidant.

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The Role of Heme Peroxo Oxidants in the Rational Mechanistic Modeling of Nitric Oxide Synthase: Characterization of Key Intermediates and Elucidation of the Mechanism

et al. 2022

View full text Add to dashboard Cite

Mammalian nitric oxide synthase (NOS) mediates the two-step O 2 -dependent oxidative degradation of arginine, and has been linked to a medley of disease situations in humans. Nonetheless, its exact mechanism of action still remains unclear. This work presents the first NOS model system where biologically proposed heme superoxo and peroxo intermediates are assessed as active oxidants against oxime substrates. Markedly, heme peroxo intermediates engaged in a bioinspired oxime oxidation reaction pathway, converting oximes to ketones and nitroxyl anions (NO À ). Detailed thermodynamic, kinetic, and mechanistic interrogations all evince a rate-limiting step primarily driven by the nucleophilicity of the heme peroxo moiety. Coherent with other findings, 18 O and 15 N isotope substitution experiments herein suffice compelling evidence toward a detailed mechanism, which draw close parallels to one of the enzymatic proposals. Intriguingly, recent enzymatic studies also lend credence to these findings, and several relevant reaction intermediates have been observed during NOS turnover.

show abstract

Bioinspired oxidation of oximes to nitric oxide with dioxygen by a nonheme iron(II) complex

Cited by 4 publications

References 43 publications

The Role of Heme Peroxo Oxidants in the Rational Mechanistic Modeling of Nitric Oxide Synthase: Characterization of Key Intermediates and Elucidation of the Mechanism

The Role of Heme Peroxo Oxidants in the Rational Mechanistic Modeling of Nitric Oxide Synthase: Characterization of Key Intermediates and Elucidation of the Mechanism

Dioxygen Reduction and Bioinspired Oxidations by Non-heme Iron(II)−α-Hydroxy Acid Complexes

The Role of Heme Peroxo Oxidants in the Rational Mechanistic Modeling of Nitric Oxide Synthase: Characterization of Key Intermediates and Elucidation of the Mechanism

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