Dioxygen transfer from 4a-hydroperoxyflavin anion. 2. Oxygen transfer to the 10 position of 9-hydroxyphenanthrene anions and to 3,5-di-tert-butylcatechol anion

Muto, Shigeaki; Bruice, Thomas C.

doi:10.1021/ja00533a028

Cited by 17 publications

(5 citation statements)

References 10 publications

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“…The UV−vis spectrum of the solution changes and a new intense band arises at 676 nm. This absorption has been assigned to the flavonoxy radical − formed in a single electron transfer from the flavonolate anion to dioxygen with the concomitant formation of superoxide anion . The presence of the flavonoxy radical could also be confirmed by EPR spectroscopy.…”

Section: Resultsmentioning

confidence: 99%

Kinetics and Mechanism of the Oxygenation of Potassium Flavonolate. Evidence for an Electron Transfer Mechanism

2000

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The oxygenation of the potassium salt of flavonol (flaH) in absolute DMF leads to potassium O-benzoylsalicylate and carbon monoxide in 95% yield at 40 degrees C. Kinetic measurements resulted in the rate law -d[flaK]/dt = k(2)[flaK][O(2)]. The rate constant, activation enthalpy, and entropy at 313.16 K are as follows: k(2)/M(-)(1) s(-1) = (3.28 +/- 0.10) x 10(-1), DeltaH()/kJ mol(-1) = 29 +/- 2, DeltaS/J mol(-1) K(-1) = -161 +/- 6. The reaction fits a Hammett linear free energy relationship for 4'-substituted flavonols, and electron-releasing groups make the oxygenation reaction faster. The anodic oxidation wave potentials E(a) of the 4'-substituted flavonolates correlate well with reaction rates. At more negative E(a) values faster reaction rates were observed. EPR spectrum of the reaction mixture (g = 2.0038, dH = 1.8 G, a(H) = 0.9 G) showed the presence of flavonoxyl radical as a result of a SET from the flavonolate to dioxygen.

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Section: Resultsmentioning

confidence: 99%

Kinetics and Mechanism of the Oxygenation of Potassium Flavonolate. Evidence for an Electron Transfer Mechanism

2000

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“…Other mechanisms like the involvement of a flavin 4,4aepoxide (Visser, 1983) or an unknown mechanism similar to the reaction between the flavin 4a-peroxide anion and a phenolate anion (Bruice, 1984b;Kemal & Bruice, 1979;Muto & Bruice, 1980, 1982 seem less likely. The flavin 4,4a-epoxide does not fit in the active site as well as the flavin 4aperoxide does, and the positioning of the reacting oxygen with respect to the substrate becomes less optimal.…”

Section: Discussionmentioning

confidence: 99%

“…The nature of this intermediate has been subject of considerable debate (Entsch et al, 1976a;Visser, 1983;Wessiak et al, 1984a,b;Bruice, 1984b;Anderson et al, 1987), but no conclusive evidence of its structure has been presented yet. Since flavin 4a-hydroperoxide is shown to be able to transfer oxygen to a variety of compounds and the flavin 4a-peroxide anion transfers dioxygen to a phenolate anion (Bruice, 1984b; Kemal & Bruice, 1979;Muto & Bruice, 1980, 1982, we assume in this study the flavin 4a-hydroperoxide to be the hydroxylating agent. The strongly absorbing intermediate might then represent a later occurring intermediate like the biradical proposed by Anderson et al (1987).…”

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confidence: 99%

Analysis of the active site of the flavoprotein p-hydroxybenzoate hydroxylase and some ideas with respect to its reaction mechanism

Schreuder¹,

Hól²,

Drenth³

1990

Biochemistry

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The flavoprotein p-hydroxybenzoate hydroxylase has been studied extensively by biochemical techniques by others and in our laboratory by X-ray crystallography. As a result of the latter investigations, well-refined crystal structures are known of the enzyme complexed (i) with its substrate p-hydroxybenzoate and (ii) with its reaction product 3,4-dihydroxybenzoate and (iii) the enzyme with reduced FAD. Knowledge of these structures and the availability of the three-dimensional structure of a model compound for the reactive flavin 4a-hydroperoxide intermediate has allowed a detailed analysis of the reaction with oxygen. In the model of this reaction intermediate, fitted to the active site of p-hydroxybenzoate hydroxylase, all possible positions of the distal oxygen were surveyed by rotating this oxygen about the single bond between the C4a and the proximal oxygen. It was found that the distal oxygen is free to sweep an arc of about 180 degrees in the active site. The flavin 4a-peroxide anion, which is formed after reaction of molecular oxygen with reduced FAD, might accept a proton from an active-site water molecule or from the hydroxyl group of the substrate. The position of the oxygen to be transferred with respect to the substrate appears to be almost ideal for nucleophilic attack of the substrate onto this oxygen. The oxygen is situated above the 3-position of the substrate where the substitution takes place, at an angle of about 60 degrees with the aromatic plane, allowing strong interactions with the pi electrons of the substrate. Polarization of the peroxide oxygen-oxygen bond by the enzyme may enhance the reactivity of flavin 4a-peroxide.

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“…The sodium salt of 3,5-di- tert -butylsemiquinone (Na + DBSQ - ) was prepared via the literature procedure by reacting 1 equiv of Na amalgam with 3,5-di- tert -butylbenzoquinone. Its UV-visible absorbance in t -BuOH is at 728 nm (580 ± 20 M -1 cm -1 , measured under N 2 ), literature 730 nm (680 M -1 cm -1 , no error bar was reported). An Na 2 S 2 O 3 aqueous solution (0.05 M) was prepared from Na 2 S 2 O 3 ·5H 2 O (Fisher Chemicals, certified ACS grade), and a pellet of KOH (Fisher Chemicals, certified ACS grade) was added for stabilization.…”

Section: Methodsmentioning

confidence: 96%

Autoxidation-Product-Initiated Dioxygenases: Vanadium-Based, Record Catalytic Lifetime Catechol Dioxygenase Catalysis

2005

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In recent work, it was shown that V-containing polyoxometalates such as (n-Bu4N)7SiW9V3O40 or (n-Bu4N)9P2W15V3O62, as well as eight other V-containing precatalysts tested, evolve to a high activity, long catalytic lifetime (> or = 30,000-100,000 total turnovers) 3,5-di-tert-butylcatechol dioxygenase, in which Pierpont's complex [VO(DBSQ)(DTBC)]2 (where DBSQ is 3,5-di-tert-butylsemiquinone and DTBC is the 3,5-di-tert-butylcatecholate dianion) was identified as a common catalyst or catalyst resting state (Yin, C.-X.; Finke, R. G. Vanadium-Based, Extended Catalytic Lifetime Catechol Dioxygenases: Evidence For a Common Catalyst. J. Am. Chem. Soc. 2005, 127 (25), 9003-9013). Herein, those findings are followed up by studies aimed at answering the following questions about this record catalytic lifetime 3,5-di-tert-butylcatechol dioxygenase catalyst: (i) What is the key to how V leaches from, for example, seemingly robust V-containing polyoxometalate precatalysts? (ii) What is the key to the sigmoidal, apparently autocatalytic kinetics observed? (iii) What can be learned about the underlying reactions that form [VO(DBSQ)(DTBC)]2? (iv) Finally, do the answers to (i-iii) lead to any broader insights or concepts? Key findings from the present work include the fact that the reaction involves a novel, autoxidation-product-induced dioxygenase, that is, one in which the undesired autoxidation of the 3,5-di-tert-butylcatechol substrate to the corresponding benzoquinone and H2O2 turns on the desired dioxygenase catalysis via a V-leaching process which eventually yields Pierpont's complex, [VO(DBSQ)(DTBC)]2. Plausible reactions en route to [VO(DBSQ)(DTBC)]2 consistent with the kinetic data, the role of H2O2, and the relevant literature are provided. The results provide a prototype example of the little observed but likely more general concept of an autoxidation-product-initiated reaction. The results also provide considerable simplification of, and insight into, the previously disparate literature of V-based 3,5-di-tert-butylcatechol dioxygenase catalysis.

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Dioxygen transfer from 4a-hydroperoxyflavin anion. 2. Oxygen transfer to the 10 position of 9-hydroxyphenanthrene anions and to 3,5-di-tert-butylcatechol anion

Cited by 17 publications

References 10 publications

Kinetics and Mechanism of the Oxygenation of Potassium Flavonolate. Evidence for an Electron Transfer Mechanism

Kinetics and Mechanism of the Oxygenation of Potassium Flavonolate. Evidence for an Electron Transfer Mechanism

Analysis of the active site of the flavoprotein p-hydroxybenzoate hydroxylase and some ideas with respect to its reaction mechanism

Autoxidation-Product-Initiated Dioxygenases: Vanadium-Based, Record Catalytic Lifetime Catechol Dioxygenase Catalysis

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