Reaction Of Quinones Research Articles

Directable regiochemistry in naphthazarins via the use of masked derivatives

The carboethoxynaphthol 3d was converted via salcomine oxidation to the masked carboethoxynaphthazarin 4b which could undergo nucleophilic addition or, if unmasked, transfer quinone reactivity to the alternative ring in form 5. The latter should undergo regiospecific Diels-Alder reactions.

Reactions of quinones and quinoid molecules with the Cp*Ru+ fragment. Electron redistribution and transposition reactions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTReactions of quinones and quinoid molecules with the Cp*Ru+ fragment. Electron redistribution and transposition reactionsYong Sheng Huang, Sylviane Sabo-Etienne, Xiao Dong He, Bruno Chaudret, Kamal Boubekeur, and Patrick BatailCite this: Organometallics 1992, 11, 9, 3031–3035Publication Date (Print):September 1, 1992Publication History Published online1 May 2002Published inissue 1 September 1992https://doi.org/10.1021/om00045a016RIGHTS & PERMISSIONSArticle Views160Altmetric-Citations22LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (631 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Determination of the position of the Qi− quinone binding from the protein surface of the cytochrome bc1 complex in Rhodobacter capsulates chromatophores

The technique of distance measurement utilizing spin relaxation enhancement by an external probe has been extended to the study of intrinsic semiquinone radicals through the use of holmium-EDTA complexes and continuous wave electron paramagnetic resonance spectroscopy. This technique has been used to determine the distance of the semiquinone anion. Q 1 (also designate as Q n − or Q c − ), from the surface of the ubiquinone cytochrome c oxidoreductase, consisting of only three subunits, in membrane particles from Rhodobacter capsulates . The location of the semiquinone anion is 6–10Åfrom the N side protein, establishing that there are two separate quinone reaction sites, i.e., ‘Q 1 ’ and ‘Q 0 ’, within this complex on opposite sides of the membrane. The results are discussed in relation to reported ENDOR, EPR, and optical studies of the mitochondrial counterpart.

Determination of the position of the Q i− quinone binding from the protein surface of the cytochrome bc1 complex in Rhodobacter capsulates chromatophores

The technique of distance measurement utilizing spin relaxation enhancement by an external probe has been extended to the study of intrinsic semiquinone radicals through the use of holmium-EDTA complexes and continuous wave electron paramagnetic resonance spectroscopy. This technique has been used to determine the distance of the semiquinone anion. Q 1 (also designate as Q n − or Q c −), from the surface of the ubiquinone cytochrome c oxidoreductase, consisting of only three subunits, in membrane particles from Rhodobacter capsulates. The location of the semiquinone anion is 6–10Åfrom the N side protein, establishing that there are two separate quinone reaction sites, i.e., ‘Q 1’ and ‘Q 0’, within this complex on opposite sides of the membrane. The results are discussed in relation to reported ENDOR, EPR, and optical studies of the mitochondrial counterpart.

Reactions of glutathione and glutathione radicals with benzoquinones

The reactions of glutathione (RSH) and glutathione radicals with a series of methyl-substituted 1,4-benzoquinones and 1,4-benzoquinone have been studied. It was found that by mixing excess benzoquinone with glutathione at pH above 6.5, the products formed were complex and unstable. All of the other experiments were carried out at pH 6.0, where the main product was stable for several hours. Stopped-flow analysis allowed the measurement of the rates of the rapid reactions between GSH and the quinones, and the products were monitored by High Performance Liquid Chromatography (HPLC). The rates of the reactions vary by five orders of magnitude and must be influenced by steric factors as well as changes in the redox states. It was observed that simple hydroquinones were not formed when the different benzoquinones were mixed with excess GSH and suggests that the initial reaction is addition/reduction rather than electron transfer. In the presence of excess quinone, the hydroquinone of the glutathione conjugate is oxidized back to its quinone. The rates of the reaction were measured. By using the technique of pulse radiolysis, it was possible to measure the reduction of the quinones by GSSG ⋅− and the oxidation of hydroquinones by GS ⋅. It is proposed that the appearance of GSSG in reactions of quinones with glutathione could be due to oxidation of the hydroquinone by oxygen and the subsequent superoxide or H 2O 2 promoting the oxidation of GSH to GSSG.

Zur Synthese und Struktur derp-Indazolchinone und ihrer Methylierungsprodukte Untersuchungen �ber Chinone, 8. Mitt.

Thep-benzoquinones5e-j react with diazomethane (after dehydrogenation) to 6-anilino-2e, dimethylamino-2h, phenylthio-2i, and methylthioindazolquinone2j. Methylation with dimethylsulfate of these as well as of the already known indazolquinones 6-toluidino-2f, 6-methylanilino-2g, 5-tert.butyl-2m, 5,6-methyl- (isomer mixture)2l,n, and benz-indazolquinone2o yield the 1-and 2-N-methyl derivatives3 and4. The structure of the 2-methyl derivatives is established by reaction of the corresponding benzoquinones with 3-methylsydnon in the case of4e,4g. UV/VIS-, IR- and1H-NMR-spectroscopy (in CDCl3 andDMSO) were used for structure determination. Comparison of the UV/VIS-spectra of2–4 shows that the indazolquinones are existing as 2 H-4,7-diones. For the structure elucidation of the 1- rs. 2-methylderivatives (whichh can be attributed to the methylation products) NMR-spectroscopy is well suited even without knowing the second isomer (solvent-effect). The course of the reaction of quinones with diazomethane and of the methylation reactions of the indazolquinones is discussed.

Molecular mechanisms for mammalian melanogenesis: Comparison with insect cuticular sclerotization

Melanogenesis is an important biochemical process for the production of skin pigments which protect many animals from the damage of solar radiation. The abnormalities in melanogenesis are associated with albinism, vitiligo, as well as malignant melanoma in humans. In the lower forms of animals viz., insects, the exoskeleton is hardened to protect their soft bodies by a process called sclerotization, which is often accompanied by melanization. Recent advances in the biochemistry of sclerotization and melanization reveal remarkable similarity between these two processes. The seven stages of sclerotization are: (a) enzymatic oxidation of N-acyldopamine, (b) Michael-1,4-addition reactions of N-acyldopamine quinone, (c) tautomerization of quinone to quinone methide, (d) Michael-1,6-addition of quinone methides, (e) tautomerization of N-acyldopamine quinone methide to 1,2-dehydro- N-acyldopamine, (f) enzymatic oxidation of 1,2-dehydro- N-acyldopamine, and (g) the reactions of resultant quinonoid compounds. Amazingly, striking similarities in the reaction sequences are found in the melanization process starting from dopa. These comparisons predict a central role for quinone methides as reactive intermediates during melanization. Accordingly, recent studies provide increasing evidence in favor of this proposition.

Nucleophilic reactions of quinones

Nucleophilic reactions of quinones

REACTION OF PHOSPHONIUM YLIDES WITH 3,5-DI-TERT-BUTYL-1,2-BENZOQUINONE

Abstract The reactions of quinone 1 with several Wittig reagents have been studied. When 1 was added to excess of 2, the corresponding 1,1,2,2-tetrabromocyclobutene derivative 4 was obtained. Reaction of 1 with moderate-stabilized ylides 5a,b at room temperature afforded the monosubstituted α,β-unsaturated esters 6, while carrying out the reaction in boiling benzene led to the formation of coumarin-derivatives 8. On the contrary, the reaction of 1 with resonance-stabilized ylides 5c,d takes place, only at higher temperature to give disubstituted α,β-unsaturated ketones 9.

NAD(P)H-NAD(P)+ Models. 73. Structure-Stereochemistry Relationship in the Reaction of NAD Analog

Abstract Four different NAD(P)H analogs have been oxidized by various substituted and unsubstituted 1,4-benzoquinones in the presence or absence of magnesium ion. The stereospecificity of the reaction depends not only on the reactivity of quinone but also on that of the analogs as well as on the presence or absence of magnesium ion. The results are discussed from the viewpoint of reaction mechanism for the transfer of a (net) hydride ion.

Convenient synthesis of quinol esters by indium-mediated Reformatsky reaction of quinones

Indium-mediated Reformatsky reaction of para-quinones gives good yields of para-quinols under mild conditions. Naturally occurring quinol esters such as jacaranone are conveniently prepared in a onepot synthesis.

ChemInform Abstract: Reaction of Benzoquinones with Cyclic Amines. 1H and 13C NMR Spectra of Amine Adducts.

AbstractThe 1,4‐benzoquinones (I) and (V) react with the cyclic amines (II) to form mixtures of the amino adducts (III) and (IV) or (VI) and (VII).

Bioreductive Activation of Quinones: Redox Properties and Thiol Reactivity

Redox properties and thiol reactivity are central to the therapeutic and toxicological properties of quinones. The use of other physicochemical parameters to establish predictive relationships for redox properties of quinones is discussed, and attention drawn to situations where such relationships may be unreliable. The rates of reaction of semiquinone radicals with oxygen, including those of chemotherapeutic agents such as mitomycin and the anthracyclines, can be predicted with reasonable confidence from the redox properties. The reactions of quinones with thiols such as glutathione produces reduced quinones and radicals, but the reactions are complex and all the features are not well understood.

Factors relevant in the reaction of pyroloquinoline quinone with amino acids

In order to reveal the stability of pyrroloquinoline quinone (PQQ) in complex samples, its reaction on incubation with amino acids was followed spectrophotometrically by monitoring oxygen consumption, and with a biological assay. For several alpha-amino acids, the formation of a yellow coloured compound (lambda max = 420 nm) was accompanied by oxygen uptake and disappearance of biological activity from the reaction mixture. The yellow product appeared to be an oxazole of PQQ, the exact structure depending on the amino acid used. Oxazole formation also occurred under anaerobic conditions with concomitant formation of PQQH2, suggesting that PQQ is able to oxidize the presumed oxazoline to the oxazole. Besides the condensation reaction, there is also a catalytic cycle in which an aldimine adduct of PQQ and the amino acid is converted into the aminophenol form of the cofactor and an aldehyde resulting from oxidative decarboxylation of the amino acid. Addition of NH4+ salts, as well as that of certain divalent cations, greatly stimulated both the cyclic and the linear reaction. With basic amino acids, oxazole formation scarcely occurred. However, as oxygen consumption was observed (provided that certain divalent cations were present), conversion of these compounds took place. A reaction scheme is proposed accounting for the products formed and the effects observed. Since NH4+ ions activate several quinoproteins (PQQ-containing enzymes) and divalent cations (Ca2+, Fe2+, and Cu2+) are additional (co)factors in certain metallo quinoproteins, the effects of metal ions observed here could be related to the mechanistic features of these enzymes. Although all oxazoles were converted to PQQ by acid hydrolysis, PQQ was not detected when hydrolysis was carried out in the presence of tryptophan, a compound which appeared to have a deleterious effect on the cofactor under this condition. The results here described explain why analysis methods for free PQQ in complex samples fail in certain cases, or are not quantitative.

O-Quinone/quinone methide isomerase: A novel enzyme preventing the destruction of self-matter by phenoloxidase-generated quinones during immune response in insects

Melanization and encapsulation of invading foreign organisms observed during the immune response in insects is known to be due to the action of activated phenoloxidase. Phenoloxidase-generated quinones are deposited either directly or after self-polymerization on foreign objects accounting for the observed reactions. Since the reactions of quinones are nonenzymatic, they do not discriminate self from nonself and hence will also destroy self-matter. In this report we present evidence for the presence of a novel quinone/quinone methide isomerase in the hemolymph of Sarcophaga bullata which destroys long-lived quinones and hence acts to protect the self-matter. Quinone methides, formed by the action of this enzyme on physiologically important quinones, being unstable undergo rapid hydration to form nontoxic metabolites.

Chemical Modifications of Biopolymers by Quinones and Quinone Methides

AbstractMany quinones and their precursors, which are transformed oxidatively into quinones and/or quinone methides, are important natural products. As secondary metabolites, they frequently possess antibiotic and cytotoxic activities, in addition to acting sometimes as pathogens. Several plants and animals, especially insects, use quinonoid substances for defense, often with spectacular results. On the macromolecular level, quinone methides have a key role in the plant kingdom in lignin biosynthesis; the biosynthesis of melanoproteins exemplifies the reactions of o‐quinones in the animal kingdom. In insects, cross‐linking of structural proteins through quinones and quinone methides results in the construction of the sclerotized exoskeleton. For mankind, the reactivity of quinones in biological systems has far‐reaching consequences of pharmaceutical, toxicological, and technical relevance. The examples in this review show that a common principle underlies these reactions, namely, the chemical modification of biopolymers. As demonstrated particularly well in a more detailed discussion of the chemical principles of insect cuticle sclerotization, several major and important new results have emerged from the development and applications of modern methods of sample separation and from solid‐state NMR spectroscopy.

Allylation of Quinones via Photoinduced Electron-Transfer Reactions from Allylstannanes

Abstract Photochemical reactions of quinones with allylstannanes provided four types of products: adducts of allyl group to the carbonyl oxygens of quinones, adducts of allyl group to the olefinic carbons, adducts of allyl group to the carbonyl carbons, and hydroquinones. An electron-transfer mechanism was confirmed by 1H-CIDNP (Chemically Induced Dynamic Nuclear Polarization) method. This study suggests that a) photoinduced electron transfer from allylstannanes to quinones produces the corresponding quinone anion radicals and tin cation radicals, b) the tin cation radicals cleave to give allyl radicals as well as tin cation, and c) the allyl radicals attack the quinone anion radicals resulting in the formation of final products, allylated quinones.

Reaction of Benzoquinones with Cyclic Amines; 1H- and 13C-Nmr Spectra of Amine-adducts

Reaction of unsymmetrical 1,4-benzoquinone with cyclic amines afforded a mixture of amine-adducts. Using dibromoquinone as the substrate, monoamine adduct was obtained regioselectively. Regiochemistry was determined by 1 H- and 13 C-nmr spectroscopic analyses

Use of Catalytic Metal‐Polyethylene Imine Complexes and Recovered Polymeric Sorbents for the Chemisorptive Removal of Polyphenols and Phenols

AbstractInvestigations of the chemisorptive properties of polyethylene imine with respect to phenol compounds have been carried out. It has been established that in the reaction of polyethylene imine with phenol compounds a three‐dimensional polymer is formed by cross‐linking and precipitates. The use of transition metal‐polyethylene imine complexes accelerates the oxidation of intermediates of the quinoid type. Results have been obtained in studying the spectral characteristics of the products of the reaction of phenols and quinones with polyethylene imine and catalytic metal‐(II)‐polyethylene imine complexes. The kinetic study of this process has shown the reaction to obey a first‐order equation.The use of a recovered sorbent, the cystein‐pretreated anion‐exchanger AB‐17‐8, for the sorption and further oxidation of phenols and quinones by the substitution of a cystein anion containing an SH‐group for an ion‐exchange polymer anion has been studied. It is suggested to employ sodium sulfite instead of cystein in order to reduce the cost of treatment and analysis of waste waters with high phenol and quinone contents.

Stereoselective 3 + 2 and stereospecific 2 + 2 cycloaddition reactions of alkenes and quinones

mM NaCl and 25 mM tris-acetate at pH 7.0.14 After 0.5 h incubation at 24 OC, 4 mM dithiothreitol was added to initiate strand cleavage. The reaction was allowed to continue for 6 h (24 C). The double strand cleavage products were separated on a 0.4% vertical agarose gel which resolves DNA segments up to 25 kbp in size (Figure 3). Therefore, DNA uniquely labeled at the R and