ESR Spectrum of a Perpendicular Benzyl Radical

Schreiner, Kurt; Berndt, A.

doi:10.1002/anie.197401441

Cited by 27 publications

(17 citation statements)

References 12 publications

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“…For example, the benzyl radical preferentially adopts a conformation in which the 2p z orbitals of all seven carbon atoms combine to form molecular orbitals that allow maximum delocalization of the unpaired electron spin. However, in the 1,1-di-tert-butylbenzyl radical, steric interactions between the bulky tert-butyl groups and the ortho aromatic hydrogens lead to a conformation in which the 2p z orbital of the benzylic carbon atom is orthogonal to the phenyl ring π-system, localizing unpaired electron spin on the benzylic carbon atom ( Figure 10A) (39). The 1,1-di-tert-butyl-2-methylallyl radical exhibits a similar conformational preference, resulting in a localized carbon-centered radical instead of a delocalized allyl radical ( Figure 10B) (40).…”

Section: Discussionmentioning

confidence: 99%

“…The major and minor bound conformers of AA-13yl in the COX-2 monomer B simulation are shown with carbons in cyan, hydrogens in gray, and oxygens in red, with the pentadienyl radical carbons (C11-C15) of the major conformer highlighted in green, and the minor in orange. Structures of benzyl and allyl radicals wherein the unpaired electron spin is either delocalized over multiple carbon atoms or localized to a single carbon atom (39,40).…”

Section: Supplementary Materialsmentioning

confidence: 99%

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Molecular Dynamics Simulations of Arachidonic Acid-Derived Pentadienyl Radical Intermediate Complexes with COX-1 and COX-2: Insights into Oxygenation Regio- and Stereoselectivity

et al. 2006

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The two cyclooxygenase enzymes, COX-1 and COX-2, are responsible for the committed step in prostaglandin biosynthesis and are the targets of the nonsteroidal antiinflammatory drugs aspirin and ibuprofen and the COX-2 selective inhibitors, Celebrex, Vioxx, and Bextra. The enzymes are remarkable in that they catalyze two dioxygenations and two cyclizations of the native substrate, arachidonic acid, with near absolute regio- and stereoselectivity. Several theories have been advanced to explain the nature of enzymatic control over this series of reactions, including suggestions of steric shielding and oxygen channeling. As proposed here, selective radical trapping and spin localization in the substrate-derived pentadienyl radical intermediate can also be envisioned. Herein we describe the results of explicit, 10 ns molecular dynamics simulations of both COX-1 and COX-2 with the substrate-derived pentadienyl radical intermediate bound in the active site. The enzymes' influence on the conformation of the pentadienyl radical was investigated, along with the accessible space above and below the radical plane and the width of several channels to the active site that could function as access routes for molecular oxygen. Additional simulations demonstrated the extent of molecular oxygen mobility within the active site. The results suggest that spin localization is unlikely to play a role in enzymatic control of this reaction. Instead, a combination of oxygen channeling, steric shielding, and selective radical trapping appears to be responsible. This work adds a dynamic perspective to the strong foundation of static structural data available for these enzymes.

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Section: Discussionmentioning

confidence: 99%

Section: Supplementary Materialsmentioning

confidence: 99%

Molecular Dynamics Simulations of Arachidonic Acid-Derived Pentadienyl Radical Intermediate Complexes with COX-1 and COX-2: Insights into Oxygenation Regio- and Stereoselectivity

et al. 2006

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“…Because the coupling constants of 8-protons in Me substituents usually have similar absolute values as those of CI -protons in these positions, the striking differences in the hyperfine data for 4a and 6 are diagnostic of the pertinent ring in 4a being twisted out of planarity with the remaining n-system (see, e.g. [7]).…”

Section: ' )mentioning

confidence: 99%

Preparation and ESR‐Spectroscopical Investigation of Remarkably Persistent Oxoisobenzofuranyl Radicals

Kruppa

Hug

Liégard

et al. 1993

Helvetica Chimica Acta

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The synthesis of the diastereoisomeric l,l'-diaryl-l,l'-bi(isobenzofuran)-3,3'( IH,l'H)-diones 3a-d starting from the readily available 2-aroylbenzoic acids l a 4 is described (Scheme I ) . Of the colourless dimers 3 a 4 , only the sterically congested 3a and 3b dissociate at ambient temperature in solution to the deep red free 3-oxoisobenzofuran-1-yl radicals 4a and 4b, respectively. The radicals 4a, b are extremely persistent in the absence of 0,. The structures of these radicals are confirmed and the coupling constants assigned by ESR and ENDOR spectroscopy and computer simulation of their ESR spectra. The dissociation equilibrium constant at 20" in toluene for 3a is determined to be 1.18' M. By studying the steady-state radical concentration as a function of temperature, the enthalpy and entropy changes for the homolytic dissociation of 3a are determined.

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“…A n~ber of persistent allyl radicals with bulky substituents have been examined by ESR [57,58]. The 1,1-di-t-butyl-2-methylallyl radical adopts the localised 'perpendicular' structure 26 which has undergone a 90 ° rotation about ~~ the CI-c 2 bond in order to minimise repulsion between the substituents on C 1 and C 2.…”

Section: Spectroscopic Detection and Spin Trappingmentioning

confidence: 99%

“…Many heavily substituted allyl radicals with slow combination rates and relatively long lifetimes are known [57,58]; the l,l,3-tri-t-butylprop~yl radical is also persistent [59].…”

mentioning

confidence: 99%

ESR studies of acyclic delocalised radicals

Walton

1984

Res Chem Intermed

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ESR Spectrum of a Perpendicular Benzyl Radical

Cited by 27 publications

References 12 publications

Molecular Dynamics Simulations of Arachidonic Acid-Derived Pentadienyl Radical Intermediate Complexes with COX-1 and COX-2: Insights into Oxygenation Regio- and Stereoselectivity

Molecular Dynamics Simulations of Arachidonic Acid-Derived Pentadienyl Radical Intermediate Complexes with COX-1 and COX-2: Insights into Oxygenation Regio- and Stereoselectivity

Preparation and ESR‐Spectroscopical Investigation of Remarkably Persistent Oxoisobenzofuranyl Radicals

ESR studies of acyclic delocalised radicals

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