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Jacques Vervoort - One of the best experts on this subject based on the ideXlab platform.
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Regioselectivity of cytochrome p 450 catalyzed hydroxylation of fluorobenzenes predicted by calculated frontier orbital substrate characteristics
Biochemistry, 1993Co-Authors: Ivonne M.c.m. Rietjens, Ans E.m.f. Soffers, Cees Veeger, Jacques VervoortAbstract:In the present study, a hypothesis is presented for the prediction of the Regioselectivity of cytochrome P-450 catalyzed hydroxylation of fluorobenzenes. The Regioselectivity of the in vivo hydroxylation of fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,2,3-trifluorobenzene, and 1,2,4-trifluorobenzene could be predicted within 6% accuracy on the basis of the substrate's frontier orbital characteristics for electrophilic attack. The in vivo Regioselectivity of the hydroxylation of fluorobenzene was not significantly influenced by changes in the cytochrome P-450 enzyme pattern. This implies that the Regioselectivity is not predominantly determined by the juxtaposition of the relatively small substrates in the active sites of the cytochrome P-450s catalyzing the reaction
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Regioselectivity of cytochrome p 450 catalyzed hydroxylation of fluorobenzenes predicted by calculated frontier orbital substrate characteristics
Biochemistry, 1993Co-Authors: Ivonne M.c.m. Rietjens, Ans E.m.f. Soffers, Cees Veeger, Jacques VervoortAbstract:In the present study, a hypothesis is presented for the prediction of the Regioselectivity of cytochrome P-450 catalyzed hydroxylation of fluorobenzenes. The Regioselectivity of the in vivo hydroxylation of fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,2,3-triluorobenzene, and 1,2,4-triflurobenzene could be predicted within 6% accuracy on the basis of the substrate's frontier orbital characteristics for electrophilic attack. The in vivo Regioselectivity of the hydroxylation of fluorobenzene was not significantly influenced by changes in the cytochrome P-450 enzyme pattern. This implies that the Regioselectivity is not predominantly determined by the juxtaposition of the relatively small substrates in the active sites of the cytochrome P-450s catalyzing the reaction. Additional in vitro experiments using 1,2-difluorobenzene as the model substrate demonstrated that minor factors influencing the Regioselectivity and possibly responsible for the 6% deviation from the calculated values in in vivo experiments might be (i) the influence of biotransformation routes occurring in vivo but not of importance in in vitro microsomal incubations and (ii) a small variation due to influences of the contribution of various cytochrome P-450 enzymes. On the basis of the results obtained, it is concluded that the aromatic hydroxylation of fluorobenzenes proceeds through an initial electrophilic attack of (FeO)3+ on the aromatic substrate, and not through initial electron abstraction followed by attack of the (FeO)2+ species on the substrate radical cation. The fact that the Regioselectivity observed could be predicted and/or explained by the site of initial (FeO)3+ attack also argues against epoxides as important intermediates in the formation of phenol metabolites from fluorobenzenes.
Ivonne M.c.m. Rietjens - One of the best experts on this subject based on the ideXlab platform.
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Regioselectivity of phase ii metabolism of luteolin and quercetin by udp glucuronosyl transferases
Chemical Research in Toxicology, 2002Co-Authors: Marelle G Oersma, H Van Der Woude, J J P Ogaards, Sjef Oere, Jacques Vervoo, Nicole H P Cnubbe, M L P S Van Iersel, P J Van Bladere, Ivonne M.c.m. RietjensAbstract:The Regioselectivity of phase II conjugation of flavonoids is expected to be of importance for their biological activity. In the present study, the Regioselectivity of phase II biotransformation of the model flavonoids luteolin and quercetin by UDP-glucuronosyltransferases was investigated. Identification of the metabolites formed in microsomal incubations with luteolin or quercetin was done using HPLC, LC-MS, and 1H NMR. The results obtained demonstrate the major sites for glucuronidation to be the 7-, 3-, 3‘-, or 4‘-hydroxyl moiety. Using these unequivocal identifications, the Regioselectivity of the glucuronidation of luteolin and quercetin by microsomal samples from different origin, i.e., rat and human intestine and liver, as well as by various individual human UDP-glucuronosyltransferase isoenzymes was characterized. The results obtained reveal that Regioselectivity is dependent on the model flavonoid of interest, glucuronidation of luteolin and quercetin not following the same pattern, depending on...
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Regioselectivity of cytochrome p 450 catalyzed hydroxylation of fluorobenzenes predicted by calculated frontier orbital substrate characteristics
Biochemistry, 1993Co-Authors: Ivonne M.c.m. Rietjens, Ans E.m.f. Soffers, Cees Veeger, Jacques VervoortAbstract:In the present study, a hypothesis is presented for the prediction of the Regioselectivity of cytochrome P-450 catalyzed hydroxylation of fluorobenzenes. The Regioselectivity of the in vivo hydroxylation of fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,2,3-trifluorobenzene, and 1,2,4-trifluorobenzene could be predicted within 6% accuracy on the basis of the substrate's frontier orbital characteristics for electrophilic attack. The in vivo Regioselectivity of the hydroxylation of fluorobenzene was not significantly influenced by changes in the cytochrome P-450 enzyme pattern. This implies that the Regioselectivity is not predominantly determined by the juxtaposition of the relatively small substrates in the active sites of the cytochrome P-450s catalyzing the reaction
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Regioselectivity of cytochrome p 450 catalyzed hydroxylation of fluorobenzenes predicted by calculated frontier orbital substrate characteristics
Biochemistry, 1993Co-Authors: Ivonne M.c.m. Rietjens, Ans E.m.f. Soffers, Cees Veeger, Jacques VervoortAbstract:In the present study, a hypothesis is presented for the prediction of the Regioselectivity of cytochrome P-450 catalyzed hydroxylation of fluorobenzenes. The Regioselectivity of the in vivo hydroxylation of fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,2,3-triluorobenzene, and 1,2,4-triflurobenzene could be predicted within 6% accuracy on the basis of the substrate's frontier orbital characteristics for electrophilic attack. The in vivo Regioselectivity of the hydroxylation of fluorobenzene was not significantly influenced by changes in the cytochrome P-450 enzyme pattern. This implies that the Regioselectivity is not predominantly determined by the juxtaposition of the relatively small substrates in the active sites of the cytochrome P-450s catalyzing the reaction. Additional in vitro experiments using 1,2-difluorobenzene as the model substrate demonstrated that minor factors influencing the Regioselectivity and possibly responsible for the 6% deviation from the calculated values in in vivo experiments might be (i) the influence of biotransformation routes occurring in vivo but not of importance in in vitro microsomal incubations and (ii) a small variation due to influences of the contribution of various cytochrome P-450 enzymes. On the basis of the results obtained, it is concluded that the aromatic hydroxylation of fluorobenzenes proceeds through an initial electrophilic attack of (FeO)3+ on the aromatic substrate, and not through initial electron abstraction followed by attack of the (FeO)2+ species on the substrate radical cation. The fact that the Regioselectivity observed could be predicted and/or explained by the site of initial (FeO)3+ attack also argues against epoxides as important intermediates in the formation of phenol metabolites from fluorobenzenes.
Jonathan M Withey - One of the best experts on this subject based on the ideXlab platform.
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strategies for the construction of morphinan alkaloid ab rings regioselective friedel crafts type cyclisations of γ aryl β benzoylamido acids with asymmetrically substituted γ aryl rings
Tetrahedron-asymmetry, 2016Co-Authors: Stephen G Davies, Euan C Goddard, Paul M Roberts, Angela J Russell, Andrew D Smith, James E Thomson, Jonathan M WitheyAbstract:Abstract The Regioselectivity of the Friedel-Crafts-type cyclisation of a range of γ-aryl-β-benzoylamido acids, bearing oxy substituents at the C(3)- and C(4)-positions of the γ-aryl ring, has been investigated. In all of the cases examined (with 3,4-dimethoxy, 3,4-methylenedioxy and 3-hydroxy-4-methoxy substituents) the Lewis acid promoted cyclisation proceeds with exclusive Regioselectivity for attack at the C(6)-position rather than at the C(2)-position, and furnishes the corresponding N - and O -protected 3-amino-6,7-dihydroxy-1-tetralone derivatives. This inherent Regioselectivity can be overturned by the regioselective introduction of chlorine as a blocking group for the C(6)-position; subsequent Lewis acid promoted cyclisation then proceeds with exclusive Regioselectivity for attack at the C(2)-position to deliver the corresponding N - and O -protected 3-amino-5-chloro-7,8-dihydroxy-1-tetralone derivative. These complementary cyclisation protocols represent useful methods for the preparation of these benzo-fused carbocyclic ring systems, which are the functionalised AB-rings of a range of morphinan alkaloids.
Jochanan Blum - One of the best experts on this subject based on the ideXlab platform.
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regioselective hydroaminomethylation of vinylarenes by a sol gel immobilized rhodium catalyst
Journal of Organic Chemistry, 2014Co-Authors: Zackaria Nairoukh, Jochanan BlumAbstract:In the course of our studies toward the development of new heterogeneous conditions for better controlling Regioselectivity in organic reactions, we investigated the application of sol-gel immobilized organometallic catalyst for regioselective hydroaminomethylation of vinylarenes with aniline or nitroarene derivatives in an aqueous microemulsion. By immobilization of 6 mol % [Rh(cod)Cl]2 within a hydrophobic silica sol-gel matrix we were able to perform efficient hydroaminomethylation under mild conditions and isolate 2-arylpropylamines with high Regioselectivity. The Regioselectivity of the reaction was found to be mainly dependent on the hydrophobicity of the catalyst support. It is also significantly affected by the electronic nature of the substrates, by the reaction temperature, and by syngas pressure. The heterogenized catalyst can be reused for several times.
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Regioselective Hydroaminomethylation of Vinylarenes by a Sol–Gel Immobilized Rhodium Catalyst
2014Co-Authors: Zackaria Nairoukh, Jochanan BlumAbstract:In the course of our studies toward the development of new heterogeneous conditions for better controlling Regioselectivity in organic reactions, we investigated the application of sol–gel immobilized organometallic catalyst for regioselective hydroaminomethylation of vinylarenes with aniline or nitroarene derivatives in an aqueous microemulsion. By immobilization of 6 mol % [Rh(cod)Cl]2 within a hydrophobic silica sol–gel matrix we were able to perform efficient hydroaminomethylation under mild conditions and isolate 2-arylpropylamines with high Regioselectivity. The Regioselectivity of the reaction was found to be mainly dependent on the hydrophobicity of the catalyst support. It is also significantly affected by the electronic nature of the substrates, by the reaction temperature, and by syngas pressure. The heterogenized catalyst can be reused for several times
Stephen G Davies - One of the best experts on this subject based on the ideXlab platform.
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strategies for the construction of morphinan alkaloid ab rings regioselective friedel crafts type cyclisations of γ aryl β benzoylamido acids with asymmetrically substituted γ aryl rings
Tetrahedron-asymmetry, 2016Co-Authors: Stephen G Davies, Euan C Goddard, Paul M Roberts, Angela J Russell, Andrew D Smith, James E Thomson, Jonathan M WitheyAbstract:Abstract The Regioselectivity of the Friedel-Crafts-type cyclisation of a range of γ-aryl-β-benzoylamido acids, bearing oxy substituents at the C(3)- and C(4)-positions of the γ-aryl ring, has been investigated. In all of the cases examined (with 3,4-dimethoxy, 3,4-methylenedioxy and 3-hydroxy-4-methoxy substituents) the Lewis acid promoted cyclisation proceeds with exclusive Regioselectivity for attack at the C(6)-position rather than at the C(2)-position, and furnishes the corresponding N - and O -protected 3-amino-6,7-dihydroxy-1-tetralone derivatives. This inherent Regioselectivity can be overturned by the regioselective introduction of chlorine as a blocking group for the C(6)-position; subsequent Lewis acid promoted cyclisation then proceeds with exclusive Regioselectivity for attack at the C(2)-position to deliver the corresponding N - and O -protected 3-amino-5-chloro-7,8-dihydroxy-1-tetralone derivative. These complementary cyclisation protocols represent useful methods for the preparation of these benzo-fused carbocyclic ring systems, which are the functionalised AB-rings of a range of morphinan alkaloids.
