Reactions Of Substituted Quinones
The reactions between methyl-substituted quinones and amines were studied by Cameron et al. [55,56]. For example, o-Xyloquinone with methylamine gave 2-methyl-3,6-bismethylamino-1,4-benzoquinone (39% yield) by displacement of a methyl by an amino-group [56]. Then, Kumanotani et al. carried out the reaction of toluquinone with excess n-butylamine [57]. Thus, the results obtained from the study gave the formation of both of 3,6-bis-(n-butylamino)-toluquinone (32%) and 2,5-bis(n-butylamino)-p-benzoquinone (8%, not including methyl group) [57]. Similarly, in the present work, methyl-p-benzoquinone 2 was reacted with primary amine 5 in equimolar ratio in EtOH and water in the presence of Na2CO3 to afford 3,5-bis(NH-substituted)-2-methyl-p-benzoquinone 8 (10%) and 2,5-bis(NH-substituted)-p-benzoquinone 9 (78%, not including methyl group). Moreover, compound 9 was synthesized in our previous study [47] but from the reaction between p-benzoquinone and primary amine 5 in equimolar ratio in dichloromethane. While CH3quinone proton and carbon signals of 8 could be observed in 1H and 13C-NMR spectra at 2.07 ppm and at 10.44 ppm, respectively, in the 1H and 13C-NMR spectra of 9, the disapperance of CH3quinone signals supported to the formation of 2,5(NH-substituted)-p-benzoquinone structure 9. Moreover, mass spectra of 8 and 9 exhibited peaks at m/z [M+H]+ = 425.3 and m/z [M+H]+ = 411.3, respectively.
reactions of substituted quinones
In the literature, there are some reports on the different location of mono- or bis- (NH) groups on the methyl-1,4-quinone moiety, which including 3,5-bis(NH-substituted)-2-methyl-p-benzoquinone, 3,6-bis(NH-substituted)-2-methyl-p-benzoquinone, 2-(NH-substituted)-6-methyl-1,4-benzoquinone, 2-(NH-substituted)-5-methyl-1,4-benzoquinone derivatives [37,58-60]. In this work, 8 has 3,5-bis(NH-substituted)-2-methyl-p-benzoquinone structure.
The reaction of 4 with 11 yielded two new amino-substituted-1,4-naphthoquinones (12 and 13), including bromine and not bromine, respectively. In the 1H-NMR spectrum of 13, a singlet appeared at 5.75 ppm, which was assignable to the proton presence of 13 instead of bromine. In addition, in the FTIR spectra of these derivatives (12 and 13) the characteristic bands observed at 1673 and 1664 cm-1 were assignable to the C=O stretching vibrations, respectively.
Compound 17 was reacted with 1-dodecanethiol 18, in the presence of triethylamine, providing both of NH- and SR- substituted-1,4-naphthoquinone 19, which including crown structure. In the proton NMR spectrum of 19, CHnapht, CHarom, and CH2crown exhibited signals in a lower field than in the starting compound 17, because of the bonding S-(CH2)11-CH3 to quinoid structure, instead of bromine.
The reaction between glutathione and 2,5-diaziridinyl-1,4-benzoquinones bearing halogen substituents at C3 and C6 was examined in terms of the formation of glutathionyl-quinone conjugates and semiquinones by HPLC with UV detection, mass spectroscopy and EPR. The reactivity of the halogen atoms toward sulfur substitution is the primary reaction leading to the formation of mono- and di-glutathionyl-substituted quinones. The relative formation of these conjugates depended on the GSH/quinone molar ratios. At GSH/quinone molar ratios below unity, the products observed were the reduced form of the parent quinone, a dithioether derivative and GSSG. Disulfide formation accounted for 60-68% of total GSH consumed. EPR analysis of these reaction mixtures showed a 5-line spectrum (1:2:3:2:1 relative intensities) with 2 equivalent N (aN = 1.98 G) and assigned to the semiquinone form of dichloro- diaziridinylbenzoquinone. Semiquinone quantification by double integration of the EPR signals and interpolation with an adequate standard revealed that the amount of semiquinone formed per GSH consumed was 0.98. At GSH/quinone molar ratios above unity (4, 10 and 100 molar excess of GSH) a pattern of products emerged consisting of 3,6-diglutathionyl quinones with two, one and no aziridinyl moieties, identified by mass spectral analysis. EPR studies revealed that these compounds were minor components of a composite EPR spectrum (a 3-line signal with 1:1:1 relative intensities, 1 equivalent N (aN = 1.73 G) and 1 H (aH = 1.45 G) or a 3-line signal with 1:2:1 relative intensities and 2 equivalent H (aH = 1.4 G). These minor components were assigned to the diglutathionyl conjugates bearing one- or no aziridinyl moiety, respectively. The major component in the EPR signal showed a 3-line spectrum (1:1:1 relative intensity) with 1 equivalent N (aN = 1.7 G) and a g shift of -0.96 G. This spectrum was assigned to a triglutathionyl conjugate of a monoaziridinylbenzoquinone. This major component was also observed when GSH/quinone mixtures were incubated with the two-electron transfer flavoprotein NAD(P)H:quinone oxidoreductase. The semiquinone signals were abolished by superoxide dismutase. In the presence of catalase, the contribution of these components to the overall EPR spectrum was equal. These data are discussed in terms of the one-electron transfer steps encompassed by thiol oxidation and semiquinone formation and the two-electron transfers inherent in sulfur substitution and aziridinyl group loss.
Rhodium-catalyzed [2 + 2 + 2] cycloadditions, sulfonyl phthalide annulations and nitroalkene reactions have been employed for the synthesis of 56 quinone-based compounds. These were evaluated against Trypanosoma cruzi, the parasite that causes Chagas disease. The reactions described here are part of a program that aims to utilize modern, versatile and efficient synthetic methods for the one or two step preparation of trypanocidal compounds. We have identified 9 compounds with potent activity against the parasite; 3 of these were 30-fold more potent than benznidazole (Bz), a drug used for the treatment of Chagas disease. This article provides a comprehensive outline of reactions involving over 120 compounds aimed at the discovery of new quinone-based frameworks with activity against T. cruzi.
Development of new methodology for the synthesis of quinones and the study of rearrangement reactions of substituted quinones. Total synthesis of physiologically active quinones and in the exploitation of quinones as intermediates in the synthesis of more complex molecules of theoretical or biological significance. Synthetic routes to the diacylmethyl-substituted quinone-hydroquinone system and investigation of their spectral and chelating properties. We are also interested in the application of computers in chemistry education. Development of multimedia based materials for teaching general and organic chemistry.
In the presence of hypervalent iodine(III) reagents such as iodobenzene diacetate (IBD) or iodobenzenedi(trifluoroacetate) (IBTA), phenols undergo oxidation to either quinones[2] or iodonium ylides.[3] Phenols with an electron-withdrawing group in the para position form the latter, while most other phenols give the former (or derivativesthereof). Direct transformation of quinone products may occur through intramolecular Diels-Alder or Michael-typereactions. Bis(phenol) substrates undergo oxidative coupling under these conditions.
Iodonium ylides are relatively stable, versatile compounds that undergo substitution and cycloaddition reactions. They are represented using two resonance forms, one zwitterionic (the "betaine" form) and the other neutral (the "ylide" form).
When the phenol contains an electron-withdrawing group in the para position and at least one ortho hydrogen, stable iodoniumylides result.[6] The initial intermediates are iodonium salts, which eliminate HZ to form the ylide. Iodonium ylidesundergo cycloaddition reactions with unsaturated functional groups, and react with nucleophiles and electrophiles to givesubstitution products.
Oxidative coupling of bis(phenols) takes place in the presence of iodine(III) reagents. The mechanismof this process is analogous to the formation of para-substituted quinones via intramolecular nucleophilicattack. Mixtures of products may result from attack at inequivalent ortho or para positions.[7]
Phenolic oxidations may afford different products depending on both the reaction conditions and the structure of the substrate. 2-Substituted phenols form ortho quinones upon oxidation. These products are unstable and undergo dimerization.[5]
When external nucleophiles are added to phenolic oxidations, further reactions of the nucleophilewith the resulting quinone may occur. Intramolecular Diels-Alder reactions have been observed in this context.[8]
Reactions with electrophiles yield iodonium salts, which may be quenched in situ by nucleophilic counteranions.In the presence of non-nucleophilic counteranions, the substituted iodonium salts can be isolated.[13]
Oxidative phenol coupling has been used for the synthesis of alkaloids related to morphine. For instance, thereaction has been employed to transform reticuline derivatives into salutaridine derivatives in a single, presumablybiomimetic, step. Yields of reactions of this type tend to be low, however.[14]
However, so far there have been no systematic experimental studies of the actual change in redox potential and solubility with different functionalization. In the present study, we have experimentally determined redox potentials and aqueous solubility of 28 different benzo/hydroquinones (BQs), naphtoquinones (NQs) and anthraquinones (AQs) in acidic, neutral and alkaline solutions along with a few nitrogen based redox species. We discuss the limitations of their properties with respect to RFB performance and discuss some of the main challenges with respect to realising all-organic RFBs.
The chemical stability of redox couples in RFBs is very important, since low life-time leads to impractical systems and increased LCES. By introducing organic molecules in high concentrations in oxidative/reductive environments, the possibility of (electro)chemical side reactions increases compared to state-of-the-art inorganic RFBs. 041b061a72
