- In Vitro Reconstitution Reveals a Central Role for the N-Oxygenase PvfB in (Dihydro)pyrazine-N-oxide and Valdiazen Biosynthesis
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The Pseudomonas virulence factor (pvf) operon is essential for the biosynthesis of two very different natural product scaffolds: the (dihydro)pyrazine-N-oxides and the diazeniumdiolate, valdiazen. PvfB is a member of the non-heme diiron N-oxygenase enzyme family that commonly convert anilines to their nitroaromatic counterparts. In contrast, we show that PvfB catalyzes N-oxygenation of the α-amine of valine, first to the hydroxylamine and then the nitroso, while linked to the carrier protein of PvfC. PvfB modification of PvfC-tethered valine was observed directly by protein NMR spectroscopy, establishing the intermediacy of the hydroxylamine. This work reveals a central role for PvfB in the biosynthesis of (dihydro)pyrazine-N-oxides and valdiazen.
- Li, Bo,Morgan, Gina L.
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supporting information
p. 21387 - 21391
(2020/09/21)
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- Nb2O5 supported on mixed oxides catalyzed oxidative and photochemical conversion of anilines to azoxybenzenes
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The synthesis of novel supported niobium oxide catalysts and their application for aniline conversion to azoxybenzenes is described. The catalysts were successfully prepared by thermal decomposition of layered double hydroxides (LDHs), containing M2+ (M = Mg2+ and/or Zn2+) and Al3+ as layer cations, followed by niobium oxide incorporation employing the wetness impregnation method. These catalysts were fully characterized by both experimental techniques and theoretical calculations, and then successfully applied to the selective conversion of anilines into azoxybenzene derivatives, with up to 98% conversion and 92% isolated yield in the presence of violet light. Control experiments and DFT calculations revealed that the catalyst has a dual role in this transformation, acting both as a Lewis acid in the oxidative step and as a photocatalyst in the dimerization of the nitrosobenzene intermediate.
- De Carvalho, Gustavo Senra Gon?alves,Chagas, Luciano Honorato,Fonseca, Carla Grijó,De Castro, Pedro P?ssa,Sant'Ana, Ant?nio Carlos,Leit?o, Alexandre Amaral,Amarante, Giovanni Wilson
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supporting information
p. 5863 - 5871
(2019/04/17)
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- Ultrasound-accelerated selective oxidation of primary aromatic amines to azoxy derivatives with trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane catalyzed by Preyssler acid-mediated nano-TiO2
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Preyssler-type heteropolyacid supported on TiO2 nanoparticles has been explored as an efficient catalyst in selective oxidation of primary aromatic amines to azoxy derivatives using trans-3,5-dihydroperoxy-3,5-dimethyl- 1,2-dioxolane as oxidant. The reactions proceeded smoothly under mild and green ultrasound-accelerated conditions to afford the products in high yields. The catalyst recovered from the reaction mixture exhibits long-term stability with no significant drop in its catalytic activity. Graphical abstract: [Figure not available: see fulltext.].
- Azarifar, Davood,Khatami, Seyed-Mola,Najminejad, Zohreh
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p. 587 - 592
(2014/04/03)
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- Synthesis of E-1-(alkoxy-NNO-azoxy)-2-arylethenes by the reaction of bis(alkoxy-NNO-azoxy)methanes with benzyl halides under conditions of phase-transfer catalysis
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Reaction of bis(methoxy- and ethoxy-NNO-azoxy)methane with benzyl halides and alkali under the conditions of a phase-transfer catalysis furnishes in one stage E-1-(alkoxy-NNO-azoxy)-2-arylethene in 21-55% yields. The intermediate products, 1,1-bis(alkoxy-NNO-azoxy)-2-arylethanes under the action of alkali eliminate one of the two alkoxy-NNO-azoxy groups with the formation of a double bond. The optimum solvent is DMSO, and as benzyl halides, benzyl chlorides. In the case of 4-bromobenzyl bromide a formation was found of a side bisbenzylation product, 1,3-bis(4-bromophenyl)-2,2-bis(methoxy-NNO-azoxy)propane.
- Zyuzin
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p. 678 - 685
(2013/07/19)
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- Reduction of nitroarenes to azoxybenzenes by potassium borohydride in water
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The synthesis of the azoxybenzenes by the reduction of nitroarenes with reducing agent potassium borohydride in water was reported for the first time. PEG-400 was used as a phase transfer catalyst and could effectively catalyze the reduction. The electronic effects of substituent groups play an important role in determining the reduction efficiencies. Electron-withdrawing substituents promote the formation of the azoxybenzene products, while electron-releasing groups retard the reductions to various degrees depending on the extent of their electron-donating ability.
- Liu, Yufang,Liu, Bo,Guo, Ailing,Dong, Zhenming,Jin, Shuo,Lu, Yun
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experimental part
p. 3563 - 3568
(2011/06/26)
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- An easy access to aromatic azo compounds under ultrasound/microwave irradiation
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Chemoselective reduction of nitroarenes to azo and azoxy compounds was easily achieved using zinc powder and ammonium chloride in DMF or DMF-water (95:5) under high intensity ultrasound (US) or microwave (MW) irradiation, separately or combined. When carried out under conventional heating the reaction required much higher temperatures and gave lower yields. The addition of a small amount of water caused a dramatic increase in the reactivity, permitting the reduction of hindered nitroarenes at the expense of selectivity. A novel reactor for combined US/MW irradiation was employed which demonstrated additional beneficial effects. Georg Thieme Verlag Stuttgart.
- Cravotto, Giancarlo,Boffa, Luisa,Bia, Marco,Bonrath, Werner,Curini, Massimo,Heropoulos, Georgios A.
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p. 2605 - 2608
(2008/09/16)
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- Selective reduction of aromatic nitro compounds to azoxy compounds with zinc/aluminium chloride reagent
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Aromatic azoxy compounds have been prepared in good yields by the selective reduction of aromatic nitro compounds with Zn/AlCl3 reagent.
- Dutta, Dilip Kumar
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p. 672 - 673
(2007/10/03)
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- Synthesis, Spectral Studies and C-S Bond Fission of Some Alkyl- Diacetates
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Some methyl and ethyl diacetates have been synthesized and their structures were identified. A correlation was found between δ-values of benzylidene protons and ?-Hammett values. The internal chemical shift of the methylene proton was found to be structural and applied field dependent. The carbon-sulfur bond fission by the action of sodium hydroxide solution in 50 percent aqueous-dioxane medium, in addition to the alkaline ester hydrolysis was studied. 2- or 4-Nitro compounds gave dicarboxyazoxybenzenes. This led to the suggestion that the reaction might proceed through two intermediates namely diacetic acid and nitrosobenzoic acid. However, the C-S bond fission of other compounds gave aldehydes, supporting that, no α-proton abstraction took place for these compounds.
- Gohar, G. A.
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- Nitrobenzyl (α-amino)phosphonates. Part 2[1]. Cleavage of 4-nitrobenzyl(α-amino)phosphonic acids in aqueous sodium hydroxide solution
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4-Nitrobenzyl(α-amino)phosphonic acids treated with an excess of aqueous sodium hydroxide undergo a C-P bond cleavage and subsequent transformation into a mixture of azoxybenzene and azobenzene derivatives. The observed cleavage is an example of the intramolecular redox reaction. The phosphonate moiety is oxidized to phosphate, and the remaining part of the molecule is reduced to azoxybenzene derivative 2. After acidification of the reaction mixture two main products were isolated; 4,4′-diformylazoxybenzene (3) and 4-formyl-4′-hydroxyazobenzene (4). The product 4 was probably formed as a result of the Wallach type rearrangement of 3.
- Boduszek, Bogdan,Halama, Agnieszka
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p. 239 - 250
(2007/10/03)
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- Oxidation of Primary Aromatic Amines, Catalyzed by Tungsten Compounds
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Treatment of o-nitroanilines and o-aminobenzoic acids with 30 percent hydrogen peroxide in the presence of Na2WO4 and H3PO4 results in selective formation of corresponding nitroso derivatives.In other cases, the products are azoxy compounds.Oxidation of anilines containing alkyl or alkoxy groups in the ortho and para positions with hydrogen peroxide in the presence of Na2WO4 and tetrabutylammonium bromide quantitatively yields corresponding nitrosobenzenes.The H2O2-Na2WO4-H3PO4 system in the presence of tetrabutylammonium bromide is proposed for preparation of nitroso derivatives from anilines containing electron-acceptor meta and para substituents.
- Mel'nikov, E. B.,Suboch, G. A.,Belyaev, E. Yu.
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p. 1640 - 1642
(2007/10/03)
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- Catalytic selective oxidation of amines with hydroperoxides over molecular sieves: Investigations into the reaction of alkylamines, arylamines, allylamines and benzylamines with H2O2 and TBHP over TS-1 and CrS-2 as the new catalyst
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The liquid phase oxidation of various substituted amines with dil H2O2 and tert-butyl hydroxyperoxide (TBHP) has been investigated over titanium and chromium silicates respectively. While TS-1/H2O2 combination exhibits a remarkable activity and selectivity in the oxidation of arylamines to produce the symmetrical azoxybenzenes, CrS-2 catalyzes the selective oxidation of various substituted amines to the corresponding nitro compounds by oxidation with 70% TBHP. The nature of the reactive intermediates during the oxidation of anilines to nitrobenzenes has been established using cyclic voltammetry experiments. Further, amines possessing α C-H bonds are selectively oxidized to either oximes or the carbonyl compounds on reaction with H2O2 catalyzed by TS-1.
- Suresh,Joseph,Jayachandran,Pol,Vinod,Sudalai,Sonawane,Ravindranathan
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p. 11305 - 11318
(2007/10/02)
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- Mechanism of the Reaction of Sodium Hydroxide and Nitrobenzylsulphones
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Aqueous sodium hydroxide reacts with sulphonyl>acetic acid (1) to give 4,4'-diformylazoxybenzene and 4,4'-dicarboxyazoxybenzene as the main products, while in 50percent water-dioxane medium the products are 4,4'-dihydroxymethylazoxybenzene, 4,4'-dicarboxyazoxybenzene besides 4-carboxy, 4'-hydroxymethylazoxybenzene and its isomer. 4-Nitrosobenzaldehyde is an intermediate in this reaction which via a Cannizzaro reaction gives the reaction products.Other 2-, 3- and 4-nitrobenzyl sulphones are studied.
- Riad, Y.,Asaad, A. Naguib,Nahas, Hind Moustafa El,Madkour, A. Emad El Din
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p. 157 - 172
(2007/10/03)
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- Peroxomonophosphoric Acid Oxidation. V. A Kinetic and Mechanistic Study of Oxidation of Aminobenzoic Acids in Acid Medium. Double Bell Shaped pH Rate Profile
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Anthranilic acid and p-aminobenzoic acid were oxidized with peroxomonophosphoric acid in aqueous acid medium to the corresponding azoxy derivatives.Suitable rate laws for the double bell shaped pH rate profile were derived and rationalized on the basis of protonation of the amino group and ionization of the carboxyl group.The mechanism of oxidation involves the nucleophilic attack of nitrogen on the electrophilic peroxo oxygen.The reactivity of the different peroxomonophosphoric acid species has been estimated.
- Panigrahi, Ganesh Prasad,Panda, Abhina Kumar
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p. 1554 - 1558
(2007/10/02)
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- Wittig Reactions of Cyanohydrines and Redox Reaction of 4-Nitromandelonitrile
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Substituted mandelonitriles 5 (R1 = H, OCH3, NO2) react in the presence of sodium tert-butoxide as a base like the corresponding aldehydes with substituted benzylidenetriphenylphosphoranes via the Wittig reaction to yield 4,4'-disubstituted stilbenes 8, for which the (E)/(Z) stereoisomer ratios are given.Our results refer to a reaction with a preceding cyanohydrine-aldehyde equilibrium. 4-Nitromandelonitrile (5a) forms in a basic methanolic solution via a redox reaction a mixture of dimethyl 4,4'-azoxybenzenedicarboxylate (11) and methyl 4-nitrobenzoate (12).
- Kossmehl, Gerhard,Nuck, Rolf
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p. 2914 - 2920
(2007/10/02)
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