Transient formation of N-alkylhemins during hemin-catalyzed epoxidation of norbornene. Evidence concerning the mechanism of epoxidation

Traylor, Teddy G.; Nakano, Taku; Miksztal, Andrew R.; Dunlap, Beth E.

doi:10.1021/ja00246a019

Cited by 63 publications

(15 citation statements)

References 3 publications

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“…In parallel with this gain of activity, the prosthetic group modification is lost, and the heme reverts to heme b. Spontaneous dealkylation of model N-alkylhemins related to Structure 2 has been also reported (44)(45)(46), though no mechanism has been proposed. In each case, the reaction amounts to an N-dealkylation of the modified heme.…”

Section: Scheme Imentioning

confidence: 99%

Mössbauer and electron paramagnetic resonance studies of chloroperoxidase following mechanism-based inactivation with allylbenzene

Debrunner

Dexter

Schulz

et al. 1996

Proc. Natl. Acad. Sci. U.S.A.

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We have used Mössbauer and electron paramagnetic resonance (EPR) spectroscopy to study a heme-Nalkylated derivative of chloroperoxidase (CPO) prepared by mechanism-based inactivation with allylbenzene and hydrogen peroxide. The freshly prepared inactivated enzyme (''green CPO'') displayed a nearly pure low-spin ferric EPR signal with g ‫؍‬ 1.94, 2.15, 2.31. The Mössbauer spectrum of the same species recorded at 4.2 K showed magnetic hyperfine splittings, which could be simulated in terms of a spin Hamiltonian with a complete set of hyperfine parameters in the slow spin fluctuation limit. The EPR spectrum of green CPO was simulated using a three-term crystal field model including g-strain. The best-fit parameters implied a very strong octahedral field in which the three 2 T 2 levels of the (3d) 5 configuration in green CPO were lowest in energy, followed by a quartet. In native CPO, the 6 A 1 states follow the 2 T 2 ground state doublet. The alkene-mediated inactivation of CPO is spontaneously reversible. Warming of a sample of green CPO to 22؇C for increasing times before freezing revealed slow conversion of the novel EPR species to two further spin S ‫؍‬ 1 ⁄2 ferric species. One of these species displayed g ‫؍‬ 1.82, 2.25, 2.60 indistinguishable from native CPO. By subtracting spectral components due to native and green CPO, a third species with g ‫؍‬ 1.86, 2.24, 2.50 could be generated. The EPR spectrum of this ''quasi-native CPO,'' which appears at intermediate times during the reactivation, was simulated using best-fit parameters similar to those used for native CPO.

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Section: Scheme Imentioning

confidence: 99%

Mössbauer and electron paramagnetic resonance studies of chloroperoxidase following mechanism-based inactivation with allylbenzene

Debrunner

Dexter

Schulz

et al. 1996

Proc. Natl. Acad. Sci. U.S.A.

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“…As addressed, the active heme site of P450 is coordinated by cysteine, which is quite unusual for a hemoprotein. However, many model compounds employed in experiments55, 56 use nonphysiological ligands, such as Cl − and CH 3 COO − instead of model cysteine ligands, such as SH or SCH 3 , because the synthesized model compound of the P450 active site is so unstable that after a few catalytic cycles, the original axial ligand is easily replaced by other molecules due to reactions with the solvent, substrate, or an oxidant 57. An exception may be the experiments reported by Nagano and coworkers, who have been successful in synthesizing model P450 compounds with axial ligands that closely mimic the cysteine ligand 58, 59.…”

Section: Introductionmentioning

confidence: 99%

Effect of the axial cysteine ligand on the electronic structure and reactivity of high‐valent iron(IV) oxo‐porphyrins (Compound I): A theoretical study

Choe

Nagase

2005

J Comput Chem

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The effect of axial ligands on the reactivity of high-valent iron(IV) oxo-porphyrins (Compound I) was investigated using the B3LYP hybrid density functional method. We studied alkane hydroxylation using four models: Compound I with thiolate, imidazole, phenolate, and chloride anions as axial ligands. The first three ligands were employed as models for cysteinate, histidine, and tyrosinate, respectively. Our calculations show that anionic ligands and neutral ligands favor different electronic states for stationary points in the reaction coordinate, and the calculated energy barrier and energy of several reaction intermediates show similar values. A remarkable effect of axial ligands was found in the final product release step. Our calculations show that the thiolate ligand weakens a bond between heme and an alcohol. In contrast, the imidazole ligand significantly increases the interaction between heme and an alcohol, which causes the catalytic cycle to be less efficient.

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“…9,33,34 In the reaction of 1a with PhIO catalysed by metalloporphyrin (7c), the formation of epoxide 3a may be explained by the formation of high valent-oxo-iron(IV) radical cation (13) from PhIO or H 2 O 2 as monooxygen donors (Scheme 2). 35 The intermediate 13, abstracts an electron to 1a to generate the olefin cation radical (15), the recombination of 14a with 15 forms the intermediate 16, which leads to 3a (Scheme 2). This was supported by the presence of a low intensity ESR signal at g = 3.85 characteristic of 13 which disappeared in the presence of 1a (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…8S(b) ESIw). 35,36 The high yields of 3a with catalysts bearing electron-withdrawing groups (7c) could be attributed to the generation of the more electrophilic and reactive intermediate (13) in the reaction, which showed greater selectivity towards electron rich olefin in 1a.…”

Section: Resultsmentioning

confidence: 99%

Chemoselective epoxidation of electron rich and electron deficient olefins catalyzed by meso-tetraarylporphyrin iron(iii) chlorides in imidazolium ionic liquids

2012

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The oxygenation of substrates containing both electron rich and electron deficient olefins (1a-b) catalyzed by 5,10,15,20-tetraarylporphyrinatoiron(III) chlorides [TAPFe(III)Cl] with H 2 O 2 gave epoxides at both electron rich and deficient olefin (2a-b, 3a-b), while with iodosyl benzene (PhIO) gave the epoxides only at electron rich olefin (3a-b) in imidazolium ionic liquids (ILs). Further reaction of 2a-b with sodium hydroxide in methanol gave 4a-b by base catalysed rearrangement of enedione epoxides. Similar reaction of 4a-b with H 2 O 2 or PhIO gave the major epoxides of electron deficient olefins and electron rich olefins. The ferric peroxy anions (TAP-Fe III -OO À ) are effective intermediates in the epoxidation of electron deficient olefins, whereas the high valent oxoferrylporphyrin p-cation radicals (TAP-Fe IV QO + ) are involved in the epoxidation of electron rich olefins. The ILs provide the special microenvironments by the interactions of cations and anions, in which the generation of the active intermediates from TAPFe(III)Cl/[Bmim] [PF 6 ] and monooxygen donors could be accelerated significantly.

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Transient formation of N-alkylhemins during hemin-catalyzed epoxidation of norbornene. Evidence concerning the mechanism of epoxidation

Cited by 63 publications

References 3 publications

Mössbauer and electron paramagnetic resonance studies of chloroperoxidase following mechanism-based inactivation with allylbenzene

Mössbauer and electron paramagnetic resonance studies of chloroperoxidase following mechanism-based inactivation with allylbenzene

Effect of the axial cysteine ligand on the electronic structure and reactivity of high‐valent iron(IV) oxo‐porphyrins (Compound I): A theoretical study

Chemoselective epoxidation of electron rich and electron deficient olefins catalyzed by meso-tetraarylporphyrin iron(iii) chlorides in imidazolium ionic liquids

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