Oxidation of thiophenol and nitroalkanes by an electron deficient isoalloxazine

Yokoe, Ichiro; Bruice, T. C.

doi:10.1021/ja00835a054

Cited by 77 publications

(37 citation statements)

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“…Values of the activation parameters indicate that the oxidation of Cu II (NP) 2 (tmeda) is a bimolecular reaction involving the associative transition state of Cu II (NP) 2 (tmeda) and molecular oxygen; k cat is substantially smaller than k s since in the former the preequilibrium constants K 1 and K 2 are also involved, and K 1 and K 2 are small. The equilibria according to Equations (15) and (16) are shifted to the left side. A comparison of the activation enthalpies and entropies of the catalytic and stoichiometric reactions clearly shows that the stoichiometric reaction is enthalpy-driven while in the case of the catalytic reaction the positive ∆S ‡ and the larger ∆H ‡ values show a different situation.…”

Section: Kinetic Measurementsmentioning

confidence: 99%

“…According to that, the first step is the formation of the complex Cu II (tmeda)(NP) 2 (2) from copper powder, 2-nitropropane, tmeda, and dioxygen [Equation (14)] or from Cu II (tmeda)(NO 2 ) 2 through substitution of NO 2 Ϫ by NP Ϫ in a pre-equilibrium in the catalytic cycle [Equation (15)]. This is then followed by an intramolecular electron transfer [Equation (16)] from the ligand 2-nitropropanate to the copper(II) ion resulting in a (2-nitropropyl radical)copper(I) complex Cu I (tmeda)(NP)(NP · ) (3). This equilibrium is largely shifted to the left (K 2 is rather small).…”

Section: Kinetic Measurementsmentioning

confidence: 99%

“…[14,15] Electron-deficient flavins also oxidise nitroalkane anions in model reactions. [16,17] Extracts of Neurospora crassa and pea seedlings oxidatively metabolise nitroethane and nitropropane, [18] and those from the hyphae of a nitrifying strain of Aspergillus flavus produce nitrite and nitrate from 2-nitropropane. [19] 2-Nitropropane and some other nitroalkanes are oxidatively denitrified by an intracellular enzyme of Hansenula mraki.…”

Section: Introductionmentioning

confidence: 99%

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Kinetics and Mechanism of the Copper-Catalysed Oxygenation of 2-Nitropropane

Balogh-Hergovich

Gréczi

Kaizer

et al. 2002

Eur. J. Inorg. Chem.

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Primary and secondary nitro compounds react with dioxygen in the presence of copper metal and N ligands such as N,N,NЈ,NЈ-tetramethylethylenediamine (tmeda), 2,2Ј-bipyridine (bpy), and 1,10-phenantroline (phen) in various solvents to form aldehydes or ketones. More coordinating solvents as well as donor N ligands accelerate the reaction remarkably. The oxygenolysis of 2-nitropropane (NPH) in the presence of copper and tmeda in DMF results in acetone and acetone oxime. The amount of tmeda influences the chemoselectivity, higher tmeda concentrations preferentially lead to the formation of the oxime. The kinetics of the reaction, measured at 90°C, resulted in a rate equation of first-order dependence on copper and dioxygen and second-order dependence on 2-nitropropane. The rate constant, activation

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Section: Kinetic Measurementsmentioning

confidence: 99%

Section: Kinetic Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Kinetics and Mechanism of the Copper-Catalysed Oxygenation of 2-Nitropropane

Balogh-Hergovich

Gréczi

Kaizer

et al. 2002

Eur. J. Inorg. Chem.

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“…This oxidation can also be performed with oxygen and light, resulting in a lower yield presumably due to secondary reactions of hyperoxide placed to the left in the case of Fl,,, independent of pH. This assumption is corroborated by the fact that enhancement of the electron deficiency inherent in Fl,, by, for example, a cyano group in position 8, leads to facile carbanion addition, as shown for nitromethane by Bruice et al [31,32].…”

Section: Results and Discussion 'Dark Reduction' Products Of 5-deazajmentioning

confidence: 77%

“…Since there is no good argument for a kinetic inhibition of carbanion addition, at least at position 4a of the normal flavin, we explain the lack of reaction between flavin and acetone by the equilibrium ( 3 ) being dis- This assumption is corroborated by the fact that enhancement of the electron deficiency inherent in Fl,, by, for example, a cyano group in position 8, leads to facile carbanion addition, as shown for nitromethane by Bruice et al [31,32].…”

Section: Modes Offlavin and Deazaflavin Reduction With Various Redumentioning

confidence: 62%

(Photo)chemistry of 5‐Deazaflavin

Duchstein

Fenner

Hemmerich

et al. 1979

European Journal of Biochemistry

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The catalytic action of 5-deazaflavin in the photochemical reduction of flavin and iron proteins [Massey, V. and Hemmerich, P. (1978) Biochemistry, 17, 9-17] is shown to be due to the highly reactive 5-deazaflavosemiquinone. This radical is generated in a complex sequence of reactions, which involves (a) covalent photoaddition of the substrate residue to the deazaflavin, (b) fast secondary photoreaction of this adduct with starting deazaflavin to yield a covalent radical dimer, accompanied by the liberation of the oxidized substrate, and (c) deazaflavin-sensitized cleavage of the radical dimer to the monomers. The structure and properties of this radical (redimerisation or dismutation) and the precursor intermediates as well as the mechanism of the photoreaction are described. Deazaflavins and their natural parent compounds are compared with respect to their different redox behavior and radical stability. The syntheses of 5-deuterated deazaflavins are described and their redox reactions are compared with those of normal deazaflavins.Among the three principal types of flavoprotein activities, i.e. (de)hydrogenation, 0 2 activation and e-transfer, only the first is retained in deazaflavoproteins, and even this to rather limited extent in most cases [l -71. The initial overestimation of deazaflavins as flavin analogs must be ascribed to the lack of chemical knowledge about this heterocyclic system. For example, Briistlein and Bruice [8] were among the first to carry out chemical studies and they concluded, from the retention of H label in the course of reduction, that deazaflavin was transferring hydride and that, by analogy, flavin was a hydride-transferring entity also. Edmondson et al. [2] have been studying the system more extensively, but they have been deceived by the fact that there is a physical analogy between the oxidized species Fl,, and dF1, which, however, does not extend to the radical HdFl nor to the fully reduced state HZdFl,,d. These authors, however, were the first to state the lack of radical stability in deazaflavoproteins as compared to natural flavoproteins. This was corroborated by the inactivity of modified D-amino acid oxidase radical produced photochemically, as reported by Jorns and Hersh [6]. Based upon theoretical studies, Sun and Song [9] claimed that 'the reactivity of position 5 is approximately independent of the identity of atom (N or C)'.On the contrary, we want to show that the analogy between flavin and deazaflavin is rather limited, deazaflavin being a 'flavin-shaped nicotinamide model ' [ 11. Spencer et al. [lo] were the first to see 'carbanion adducts' and 'two-electron disproportionation', a phenomenon which should rather be termed 'interdeazaflavin hydride transfer'. This study does not yield much information on the half-reduced deazaflavin. Radicals do not occur as essential intermediates in deazaflavin-linked oxidoreduction, unless enforced le--transfer methods are applied, as we will show below.Based on our new and simple synthesis of the deazaflavin skeleton [ll], ...

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Mechanism of Action of Glutathione‐Dependent Enzymes

Douglas

1987

Advances in Enzymology - And Related Areas of Molecular Biology

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Oxidation of thiophenol and nitroalkanes by an electron deficient isoalloxazine

Cited by 77 publications

References 1 publication

Kinetics and Mechanism of the Copper-Catalysed Oxygenation of 2-Nitropropane

Kinetics and Mechanism of the Copper-Catalysed Oxygenation of 2-Nitropropane

(Photo)chemistry of 5‐Deazaflavin

Mechanism of Action of Glutathione‐Dependent Enzymes

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