- The Trapping of the OH Radical by Coenzyme Q. A Theoretical and Experimental Study
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Several pathways for the attack of the hydroxyl radical on coenzyme Q, as a prototypical chemical reaction involved in biological antioxidant actions, were theoretically analyzed by hybrid density functional theory computations, at the BHandHLYP/6-31G level. We found that the most favorable pathways are the hydrogen abstraction reaction from the phenolic hydrogen on the reduced form (ubiquinol), and the electrophilic OH addition on the oxidized form (ubiquinone). The reaction paths for the two mechanisms were traced independently. Following the direct dynamics method, the respective thermal rate constants were calculated using variational transition-state theory with multidimensional small-curvature tunneling. The experimental rate constants for the reaction of ubiquinol and ubiquinone with hydroxyl radicals produced via the Fenton's reaction in phosphate-buffered water solution at pH 7 were also measured. We found, first, that the reactivity in gas-phase (theoretical approach) is dominated by the OH addition mechanism on ubiquinone, and second, that a good agreement exists between the ratio of the rate constants determined from theoretical and experimental approaches for the reaction of oxidized and reduced forms of coenzyme Q with hydroxyl radicals. It is a very fast reaction, practically diffusion-controlled, with an inverse dependence of the thermal rate constants on temperature and therefore, a negative activation energy, both theoretically and experimentally. The influence of the tunneling factor was negligible. The analysis of the enthalpy and entropy contributions to the Gibbs free energy profile allowed us to understand the negative value of the activation energy.
- Espinosa-Garcia,Gutierrez-Merino
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Read Online
- Catalytic formation of hydrogen peroxide from coenzyme NADH and dioxygen with a water-soluble iridium complex and a ubiquinone coenzyme analogue
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A ubiquinone coenzyme analogue (Q0: 2,3-dimethoxy-5-methyl-1,4-benzoquinone) was reduced by coenzyme NADH to yield the corresponding reduced form of Q0 (Q0H2) in the presence of a catalytic amount of a [C,N] cyclometalated organoiridium complex (1: [IrIII(Cp?)(4-(1H-pyrazol-1-yl-κN2)benzoic acid-κC3)(H2O)]2SO4) in water at ambient temperature as observed in the respiratory chain complex I (Complex I). In the catalytic cycle, the reduction of 1 by NADH produces the corresponding iridium hydride complex that in turn reduces Q0 to produce Q0H2. Q0H2 reduced dioxygen to yield hydrogen peroxide (H2O2) under slightly basic conditions. Catalytic generation of H2O2 was made possible in the reaction of O2 with NADH as the functional expression of NADH oxidase in white blood cells utilizing the redox cycle of Q0 as well as 1 for the first time in a nonenzymatic homogeneous reaction system.
- Suenobu, Tomoyoshi,Shibata, Satoshi,Fukuzumi, Shunichi
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- A ubiquinol-based charge-transfer complex obtained from a solvent-free approach
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Quinones (=cyclohexa-2,5-diene-1,4-diones) and hydroquinones (=benzene-1,4-diols) belong to species that are balanced between their redox character and their ability to build supramolecular complexes. Considering the ubiquinol 2,3-dimethoxy-5-methyl-1,4-dihydroquinone (=2,3-dimethoxy-5- methylbenzene-1,4-diol; 1), the tendency to undergo an oxidation side reaction was overcome by combining this electron-donating species 1 with a nonreactive partner, benzene-1,2,4,5-tetracarbonitrile (TCNB; 3), to yield a 2 : 1 charge-transfer (CT) complex 4. This work illustrates how very convenient the solvent-free techniques are to access intermolecular species. X-Ray diffraction studies revealed that pure ubiquinol 1 (structure included) crystallizes in two enantiomeric conformations, while the triads 4 formed with TCNB (3) exist as meso forms assembled via H-bonds in zigzag-chains patterns.
- Bouvet, Marcel,Malezieux, Bernard,Herson, Patrick,Villain, Francoise
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- Superoxide Dismutase Inhibition of Oxidation of Ubiquinol and Concomitant Formation of Hydrogen Peroxide
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We measured ubiquinone (CoQ0) and hydrogen peroxide (H2O2) formed in the process of oxidation of ubiquinol (CoQ0H2). We found that copper-zinc superoxide dismutase and manganese superoxide dismutase inhibited both the CoQ0 formation and the H2O2 formation only in the presence of chelators such as DTPA (diethylenetriaminepentaacetic acid). The amount of H2O2 was almost equal to that of CoQ0, indicating that the H2O2 formation was coupled with the CoQ0 formation. The lack of inhibitory effects of the corresponding heat-inactivated superoxide dismutase (SOD) confirmed that the inhibition by the original SOD was due to its enzymatic activity. We propose that CoQ0H2 oxidation occurs as a chain reaction with superoxide as the chain carrier and that SOD inhibits this reaction by lowering the superoxide concentration.
- Nakayama, Tsutomu,Hashimoto, Miku,Hashimoto, Kei
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Read Online
- SPERMINE PRO-DRUGS
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Disclosed herein are novel spermine prodrugs and methods of use for treating subjects exhibiting symptoms of a low spermine disorder. Also disclosed are methods of synthesizing spermine prodrugs. Compositions containing spermine prodrugs are also disclosed.
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Paragraph 0011
(2021/01/26)
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- Development of a Redox-Sensitive Spermine Prodrug for the Potential Treatment of Snyder Robinson Syndrome
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Snyder Robinson Syndrome (SRS) is a rare disease associated with a defective spermine synthase gene and low intracellular spermine levels. In this study, a spermine replacement therapy was developed using a spermine prodrug that enters cells via the polyamine transport system. The prodrug was comprised of three components: a redox-sensitive quinone "trigger", a "trimethyl lock (TML)"aryl "release mechanism", and spermine. The presence of spermine in the design facilitated uptake by the polyamine transport system. The quinone-TML motifs provided a redox-sensitive agent, which upon intracellular reduction generated a hydroquinone, which underwent intramolecular cyclization to release free spermine and a lactone byproduct. Rewardingly, most SRS fibroblasts treated with the prodrug revealed a significant increase in intracellular spermine. Administering the spermine prodrug through feeding in a Drosophila model of SRS showed significant beneficial effects. In summary, a spermine prodrug is developed and provides a lead compound for future spermine replacement therapy experiments.
- Phanstiel, Otto,Sekhar, Vandana,Tantak, Mukund P.,Tao, Xianzun,Zhai, R. Grace
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p. 15593 - 15607
(2021/11/16)
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- Metal-free reduction of unsaturated carbonyls, quinones, and pyridinium salts with tetrahydroxydiboron/water
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A series of unsaturated carbonyls, quinones, and pyridinium salts have been effectively reduced to the corresponding saturated carbonyls, dihydroxybenzenes, and hydropyridines in moderate to high yields with tetrahydroxydiboron/water as a mild, convenient, and metal-free reduction system. Deuterium-labeling experiments have revealed this protocol to be an exclusive transfer hydrogenation process from water. This journal is
- Li, Tiejun,Peng, Henian,Tang, Wenjun,Tian, Duanshuai,Xu, Guangqing,Yang, He
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p. 4327 - 4337
(2021/05/31)
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- 1-Methyl-1,4-cyclohexadiene as a Traceless Reducing Agent for the Synthesis of Catechols and Hydroquinones
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Pro-aromatic and volatile 1-methyl-1,4-cyclohexadiene (MeCHD) was used for the first time as a valid H-atom source in an innovative method to reduce ortho or para quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields. Notably, the excess of MeCHD and the toluene formed as the oxidation product can be easily removed by evaporation. In some cases, trifluoroacetic acid as a catalyst was added to obtain the desired products. The reaction proceeds in air and under mild conditions, without metal catalysts and sulfur derivatives, resulting in an excellent and competitive method to reduce quinones. The mechanism is attributed to a radical reaction triggered by a hydrogen atom transfer from MeCHD to quinones, or, in the presence of trifluoroacetic acid, to a hydride transfer process.
- Baschieri, Andrea,Amorati, Riccardo,Valgimigli, Luca,Sambri, Letizia
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p. 13655 - 13664
(2019/10/28)
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- Catalytic Electrophilic Alkylation of p-Quinones through a Redox Chain Reaction
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Allylation and benzylation of p-quinones was achieved through an unusual redox chain reaction. Mechanistic studies suggest that the existence of trace hydroquinone initiates a redox chain reaction that consists of a Lewis acid catalyzed Friedel–Crafts alkylation and a subsequent redox equilibrium that regenerates hydroquinone. The electrophiles could be various allylic and benzylic esters. The addition of Hantzsch ester as an initiator improves the efficiency of the reaction.
- Xu, Xiao-Long,Li, Zhi
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supporting information
p. 8196 - 8200
(2017/06/30)
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- QUINONE BASED NITRIC OXIDE DONATING COMPOUNDS
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The present invention relates to nitric oxide donor compounds having a quinone based structure, to processes for their preparation and to their use in the treatment and/or prophylaxis of glaucoma and ocular hypertension.
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Page/Page column 39; 40
(2015/11/18)
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- RESORUFIN DERIVATIVES FOR TREATMENT OF OXIDATIVE STRESS DISORDERS
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Disclosed herein are resorufin derivative compounds and methods of using such compounds for treating or suppressing oxidative stress disorders, including mitochondrial disorders, impaired energy processing disorders, neurodegenerative diseases and diseases of aging.
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Paragraph 0132
(2014/09/29)
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- QUINONE BASED NITRIC OXIDE DONATING COMPOUNDS FOR OPHTHALMIC USE
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The present invention relates to nitric oxide donor compounds having a quinone based structure of formula (I), wherein R1 to R6, n, m and p are as defined in claim 1, compositions thereof and said compounds for use in the treatment and/or prophylaxis of glaucoma and ocular hypertension.
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Page/Page column 60
(2014/11/11)
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- QUINONE BASED NITRIC OXIDE DONATING COMPOUNDS
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The present invention relates to nitric oxide donor compounds having a quinone based structure of formula (I), wherein R1 to R6, m, n and p are as defined in claim 1, to processes for their preparation and to their use in the treatment of pathological conditions where a deficit of NO plays an important role in their pathogenesis, such as pulmonary arterial hypertension, Sickle cell disease, systemic sclerosis and scleroderma, muscular dystrophies, Duchenne's muscular dystrophy and Becker's muscular dystrophy, vascular dysfunctions.
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Page/Page column 63
(2014/11/11)
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- In situ spectroeletrochemistry and cytotoxic activities of natural ubiquinone analogues
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Quinones are a group of potent antineoplastic agents. Here we described effective and facile routes to synthesize a series of ubiquinone analogues (UQAs). These unique compounds have been investigated by electrochemistry and in situ UV-vis spectroelectrochemistry to explore their electron-transfer processes and radical properties in aprotic media. The structure-activities relationships of inhibiting cancer cell proliferation of UQAs were examined in murine melanoma B16F10 cells using a 72 h continuous exposure MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. Our results revealed that UQAs had improved antiproliferative activity and displayed better inhibitory effects than natural ubiquinone 10. The cytotoxic activities of UQAs were correlated to the semiubiquinone radicals, which were confirmed by in situ electron spin resonance (ESR). In the cytotoxicity test, 6-vinylubiquinone 5 and 6-(4′-fluorophenyl) ubiquinone 7 that possess half maximal inhibitory concentration value (IC50) of 6.1 μM and 6.2 μM. This would make them as valuable candidates for future pharmacological studies.
- Ma, Wei,Zhou, Hao,Ying, Yi-Lun,Li, Da-Wei,Chen, Guo-Rong,Long, Yi-Tao,Chen, Hong-Yuan
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experimental part
p. 5990 - 6000
(2011/09/19)
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- Reversible redox of NADH and NAD+ at a hybrid lipid bilayer membrane using ubiquinone
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Here, we report the reversible interconversion between NADH and NAD + at a low overpotential, which is in part mediated by ubiquinone embedded in a biomimetic membrane to mimic the initial stages of respiration. This system can be used as a platform to examine biologically relevant electroactive molecules embedded in a natural membrane environment and provide new insights into the mechanism of biological redox cycling.
- Ma, Wei,Li, Da-Wei,Sutherland, Todd C.,Li, Yang,Long, Yi-Tao,Chen, Hong-Yuan
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supporting information; experimental part
p. 12366 - 12369
(2011/10/02)
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- Bis-coenzyme Q0: Synthesis, characteristics, and application
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A methylene-bridged bis-coenzyme Q0, bis(2,3-dimethoxy-5-methyl- l,4-benzoquinone)methane (Bis-CoQ0), that shows intramolecular electronic communications has been synthesized for the first time. By employing electrochemical, in situ UV/Vis, and electron paramagnetic resonance (EPR) spectroelectrochemical techniques, the unstable reduced intermediate speciesa-monoradicals, diamagnetic dianions and tetraanions of Bis-CoQ 0a-have been observed. The electron-transfer process can be defined as a three-step reduction process with a total of four electrons in solution in CH3CN. The chemical reaction in the third redox step process was confirmed by variable temperature cyclic voltammetry. In an aprotic CH 3CN solution, the peak potential separation between electron-transfer steps diminished sequentially with increasing concentration of water. The hydrogen-bonding interactions between water and the electrochemically reduced intermediates of Bis-CoQ0 can be estimated by peak potential shifts. The electronic communications of Bis-CoQ0 may have been blocked when one reduction peak was observed with proper quantities of water in CH 3CN solution. The antioxidant defense capacity of Bis-CoQ 0-protected cells has also been assessed.
- Wang, Xiuwen,Ma, Wei,Ying, Yilun,Liang, Jie,Long, Yi-Tao
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supporting information; experimental part
p. 1064 - 1073
(2011/10/11)
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- Type II NADH dehydrogenase of the respiratory chain of Plasmodium falciparum and its inhibitors
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Plasmodium falciparum NDH2 (pfNDH2) is a non-proton pumping, rotenone-insensitive alternative enzyme to the multi-subunit NADH:ubiquinone oxidoreductases (Complex I) of many other eukaryotes. Recombinantly expressed pfNDH2 prefers coenzyme CoQ0 as an acceptor substrate, and can also use the artificial electron acceptors, menadione and dichlorophenol-indophenol (DCIP). Previously characterized NDH2 inhibitors, dibenziodolium chloride (DPI), diphenyliodonium chloride (IDP), and 1-hydroxy-2-dodecyl-4(1H)quinolone (HDQ) do not inhibit pfNDH2 activity. Here, we provide evidence that HDQ likely targets another P. falciparum mitochondrial enzyme, dihydroorotate dehydrogenase (pfDHOD), which is essential for de novo pyrimidine biosynthesis.
- Dong, Carolyn K.,Patel, Vishal,Yang, Jimmy C.,Dvorin, Jeffrey D.,Duraisingh, Manoj T.,Clardy, Jon,Wirth, Dyann F.
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supporting information; experimental part
p. 972 - 975
(2009/08/15)
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- Novel Intermediates Useful for the Preparation of Coenzymes, Process for the Preparation of Novel Intermediates and an Improved Process for the Preparation of Coenzymes
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The present invention relates to novel intermediates for the preparation of coenzymes, processes for the preparation of the intermediates and an improved process for the preparation of Coenzymes. The present invention particularly relates to an improved process for the preparation of Coenzyme Q, more particularly for Conenzyme Q9 and Coenzyme Q10. Still more particularly this invention relates to regio and stereo controlled process for the preparation of Coenzyme Q9 and Coenzyme Q10 of the formula I where n=9 (Coenzyme CoQ9), and where n=10. (Coenzyme CoQ10)
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Page/Page column 14-16
(2008/12/08)
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- Reaction of phenols with the 2,2-diphenyl-1-picrylhydrazyl radical. Kinetics and DFT calculations applied to determine ArO-H bond dissociation enthalpies and reaction mechanism
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(Figure Presented) The formal H-atom abstraction by the 2,2-diphenyl-1-picrylhydrazyl (dpph?) radical from 27 phenols and two unsaturated hydrocarbons has been investigated by a combination of kinetic measurements in apolar solvents and density functional theory (DFT). The computed minimum energy structure of dpph? shows that the access to its divalent N is strongly hindered by an ortho H atom on each of the phenyl rings and by the o-NO2 groups of the picryl ring. Remarkably small Arrhenius pre-exponential factors for the phenols [range (1.3-19) × 105 M-1 s-1] are attributed to steric effects. Indeed, the entropy barrier accounts for up to ca. 70% of the free-energy barrier to reaction. Nevertheless, rate differences for different phenols are largely due to differences in the activation energy, Ea,1 (range 2 to 10 kcal/mol). In phenols, electronic effects of the substituents and intramolecular H-bonds have a large influence on the activation energies and on the ArO-H BDEs. There is a linear Evans-Polanyi relationship between E a,1 and the ArO-H BDEs: Ea,1/kcal x mol-1 = 0.918 BDE(ArO-H)/kcal x mol-1 - 70.273. The proportionality constant, 0.918, is large and implies a "late" or "product-like" transition state (TS), a conclusion that is congruent with the small deuterium kinetic isotope effects (range 1.3-3.3). This Evans-Polanyi relationship, though questionable on theoretical grounds, has profitably been used to estimate several ArO-H BDEs. Experimental ArO-H BDEs are generally in good agreement with the DFT calculations. Significant deviations between experimental and DFT calculated ArO-H BDEs were found, however, when an intramolecular H-bond to the O? center was present in the phenoxyl radical, e.g., in ortho semiquinone radicals. In these cases, the coupled cluster with single and double excitations correlated wave function technique with complete basis set extrapolation gave excellent results. The TSs for the reactions of dpph ? with phenol, 3- and 4-methoxyphenol, and 1,4-cyclohexadiene were also computed. Surprisingly, these TS structures for the phenols show that the reactions cannot be described as occurring exclusively by either a HAT or a PCET mechanism, while with 1,4-cyclohexadiene the PCET character in the reaction coordinate is much better defined and shows a strong π-π stacking interaction between the incipient cyclohexadienyl radical and a phenyl ring of the dpph? radical.
- Foti, Mario C.,Daquino, Carmelo,Mackie, Iain D.,DiLabio, Gino A.,Ingold
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experimental part
p. 9270 - 9282
(2009/04/07)
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- Synthetic studies on coenzyme Q10: Part 1 - An efficient and highly stereocontrolled synthesis of coenzyme Q10 via a C 5+C45 strategy
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A practical, highly stereoselective ten-step synthesis of coenzyme Q 10 (1) has been accomplished (overall yield ca. 28%), starting from commercially available 2,3-dimethoxy-5-methylbenzoquinone (Scheme). The introduction of the first side-chain isoprenyl group with (E)-configuration (compound 6) was realized by means of a coupling reaction of the aromatic system 3 with oxirane, followed by Swern oxidation and Wittig olefination. The tosyl (Ts) group in the sulfone 9 was selectively removed with sodium naphthalenide in THF to afford 1.
- Yu, Xiong-Jie,Chen, Fen-Er,Dai, Hui-Fang,Chen, Xu-Xiang,Kuang, Yun-Yan,Xie, Bin
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p. 2575 - 2581
(2007/10/03)
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- 2,3-Dimethoxy-5-methyl-1,4-benzoquinones and 2-methyl-1,4-naphthoquinones: Glycation inhibitors with lipid peroxidation activity
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Anti-glycation activity of our anti-oxidant quinone library was measured and several 2,3-dimethoxy-5-methyl-1,4-benzoquinones and 2-methyl-1,4- naphthoquinones were identified as novel inhibitors of glycation, of which 2,3-dimethoxy-5-methyl-1,4-benzoquinones 13b is the most potent glycation inhibitor with around 50 μM of the IC50 value.
- Jung, Young-Sik,Joe, Bo-Young,Cho, Sung Ju,Konishi, Yasuo
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p. 1125 - 1129
(2007/10/03)
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- Effects of new ubiquinone-imidazo[2,1-b]thiazoles on mitochondrial complex I (NADH-ubiquinone reductase) and on mitochondrial permeability transition pore
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In this work we describe the synthesis of a series of imidazo[2,1-b] thiazoles and 2,3-dihydroimidazo[2,1-b]thiazoles connected by means of a methylene bridge to CoQ0. These compounds were tested as specific inhibitors of the NADH:ubiquinone reductase activity in mitochondrial membranes. The imidazothiazole system when bound to the quinone ring in place of the isoprenoid lateral side chain, may increase the inhibitory effect (with an IC50 for NADH-Q1 activity ranging between 0.25 and 0.96 μM) whereas the benzoquinone moiety seems to lose the capability to accept electrons from complex I as indicated by very low maximal velocity elicited by the compounds tested. Moreover the low rotenone sensitivity for almost all of these compounds suggests that they are only partially able to interact with the physiological ubiquinone-reduction site. The compounds were investigated for the capability of increasing the permeability transition of the inner mitochondrial membrane in isolated mitochondria. Unlike CoQ0, which is considered a mitochondrial membrane permeability transition inhibitor, the new compounds were inducers.
- Andreani, Aldo,Granaiola, Massimiliano,Leoni, Alberto,Locatelli, Alessandra,Morigi, Rita,Rambaldi, Mirella,Recanatini, Maurizio,Lenaz, Giorgio,Fato, Romana,Bergamini, Christian
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p. 5525 - 5532
(2007/10/03)
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- The preparation of side chain functionalized analogues of coenzyme Q for protein conjugation studies
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The synthesis of two analogues of CoQ (10 and 13) suitable for conjugation to a peptide or protein, and hence the development of an ELISA immunoassay, is presented. These analogues were synthesized from the protected quinone, 1-bromo-2-methyl-3,4,5,6-tetramethoxybenzene (1), itself prepared from commercially available CoQ-0 (3). Model coupling studies of one of the analogues (10) to N-acetyl-L-lysine methyl ester and a lysine containing dipeptide (N-acetylglycine-L-lysine methyl ester) were also undertaken as a first step to monoclonial antibody production.
- Daines, Alison M.,Abell, Andrew D.
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p. 2371 - 2375
(2007/10/03)
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- Photoreduction of p-Benzoquinones: Effects of Alcohols and Amines on the Intermediates and Reactivities in Solution
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The photochemistry of 1,4-benzoquinone (BQ) and alkyl-, Cl- and related derivatives, e.g. methyl-, 2,6-dimethyl-, chloro-, 2,5-dichloro-1,4-benzoquinone, duroquinone and chloranil, was studied in nonaqueous solvents by UV-vis spectroscopy using nanosecond laser pulses at 308 nm. The reactivity of the triplet state (3Q*) of the quinones with 2-propanol in the absence of water is largest for BQ and depends mainly on the quinone structure, whereas the rate constant of electron transfer from amines, such as triethylamine (TEA) or 1,4-diazabicyclo[2.2.2]octane, is close to the diffusion-controlled limit for BQ and most derivatives. Photoinduced charge separation after electron transfer from amines to 3Q* and the subsequent charge recombination or neutralization are supported by time-resolved conductivity measurements. The half-life of the decay kinetics of the semiquinone radical (.QH/Q.-) depends significantly on the donor and the medium. The photoconversion into the hydroquinones was measured under various conditions, the quantum yield, λirr = 254 nm, increases with increasing 2-propanol and TEA concentrations. The effects of quenching of 3Q*, the .QH/Q.- radicals and the photoconversion are outlined. The mechanisms of photoreduction of quinones in acetonitrile by 2-propanol are compared with those by TEA in benzene and acetonitrile, and the specific properties of substitution are discussed.
- Goerner, Helmut
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p. 440 - 448
(2007/10/03)
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- A convergent approach to coenzyme Q
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Syntheses of coenzyme Q3-8 are described, as well as related systems such as plastoquinone-5. Preparation of the higher homologues of the ubiquinones relies on two new conjunctive reagents, or "linchpins", each of which ultimately corresponds to two or three prenyl units. These allow for attachment of a polyprenyl halide at one end, followed by a Ni(0)-catalyzed cross-coupling at the other terminus with a chloromethylated p-quinone.
- Lipshutz, Bruce H.,Bulow, Gerd,Fernandez-Lazaro, Fernando,Kim, Sung-Kyu,Lowe, Richard,Mollard, Paul,Stevens, Kirk L.
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p. 11664 - 11673
(2007/10/03)
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- An expeditious route to CoQ(n), Vitamins K1 and K2, and related allylated para-quinones utilizing Ni(0) catalysis
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Coupling reactions between vynylalanes and chloromethylated para-quinones, mediated by catalytic amounts of Ni(0), lead directly to allylated products, including coenzyme Q, and vitamins K1 and K2.
- Lipshutz, Bruce H.,Kim, Sung-Kyu,Mollard, Paul,Stevens, Kirk L.
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p. 1241 - 1253
(2007/10/03)
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- Allylated aromatics via Ni-catalyzed couplings of benzylic chlorides and vinylic organometallics
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Hydroalumination and hydrozirconation of alkynes lead to vinylic organometallics which react with benzylic chlorides at room temperature under the influence of in situ-generated, catalytic quantities of (presumably) Ni(O), to afford allylated aromatics in good yields.
- Lipshutz, Bruce H.,Buelow, Gerd,Lowe, Richard F.,Stevens, Kirk L.
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p. 7265 - 7276
(2007/10/03)
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- SPECTROSCOPIC STUDY OF THE PHOTOCHEMICAL AND CHEMICAL GENERATION OF RADICAL MOIETIES IN A SOLUTION OF UBIQUINONE-0
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Key words: laser flash photolysis; absorption spectrum; anion-radical; ubiquinone-0.
- Plyusnin, V. F.,Samoilova, R. I.,Grivin, V. P.
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p. 240 - 245
(2007/10/03)
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- The surprisingly high reactivity of phenoxyl radicals
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Rate constants have been measured in nonaqueous media for hydrogen atom abstraction by the phenoxyl radical from some biologically important phenols and related compounds. Although the thermochemistry for these reactions must be very similar to the thermochemistry for H atom abstraction from the same substrate by a peroxyl radical, the phenoxyl rate constants, k5, are ca. 100-300 times greater than the (already well-known) peroxyl rate constants, k1. For example, with α-tocopherol in benzene/di-tert-butyl peroxide (1:3, v/v) k5293K = 1.1 × 109 M-1 s-1 vs k1303K = 3.2 × 106 M-1 s-1 in a similar nonpolar medium, and with ubiquinol-10 in the same solvent mixture k5293k = 8.4 × 107 M-1 s-1, while the corresponding value for k1 is 3.5 × 105 M-1 s-1. The greater reactivity of the phenoxyl radical has been traced to the fact that the Arrhenius preexponential factors are much larger than for the corresponding peroxyl radical reactions, i.e., A5 ～ 102A1. For example, with α-naphthol log(A5/M-1 s-1) = 8.9 and E5 = 2.2 kcal/mol vs log(A1/M-1 s-1) = 6.4 and E1 = 1.7 kcal/mol. The preexponential factors for H-atom donors more reactive than α-naphthol are even greater; for example, with α-tocopherol in CH3CN/di-tert-butyl peroxide (1:2, v/v) log(A5/M-1 s-1) = 10.0 and E5 = 2.0 kcal/mol, and with ubiquinol-0 in benzene/di-tert-butyl peroxide (1:3, v/v) log(A5/M-1 s-1) = 10.5 and E5 = 3.5 kcal/mol. The role that intermediate hydrogen-bonded complexes between the reacting radical and the phenolic hydrogen donor may play in these reactions is discussed, and it is pointed out that our results are likely to be relevant to in vivo radical chemistry.
- Foti,Ingold,Lusztyk
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p. 9440 - 9447
(2007/10/02)
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- Reduction Kinetics of 2,3-Dimethoxy-5-methyl-1,4-Benzoquinone by Ascorbic Acid in Acid Solution
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The mechanism of the oxidation of ascorbic acid by 2,3-dimethoxy-5-methyl-1,4-benzoquinone was studied as a function of pH, ionic strength and temperature in aqueous buffer solutions, using dc polarography and UV-VIS spectrophotometry.The study was performed at pH values 3.0 - 6.2 at which the quinone is stable.From the experimental results, a mechanism for oxidation of the ascorbic acid which involves several steps with the participation of AH. and QH. radicals as intermediate species, has been proposed.
- Cano, Maria Constanza Soriano,Sanchez, Juan Vera
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p. 427 - 430
(2007/10/02)
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- Synthesis of isotopically labelled ubiquinones
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Ubiquinones (1) of various chain lengths have been synthesized. The key step involves the condensation of a long chain polyunsaturated alcohol onto an aromatic intermediate. The synthetic methodology allows for the incorporation of isotopic labels in the methoxy groups attached to the ring portion of the molecule.
- Duralski, Andrzej A.,Watts, Anthony
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p. 4983 - 4984
(2007/10/02)
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- Therapeutic agent for liver disease and piperazine derivatives
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A therapeutic agent for liver disease containing as an active ingredient a piperazine derivative having the formula: STR1 wherein, A represents a phenyl, p-benzoquinonyl or cumarinyl group which may have at least one substituent selected from the group consisting of halogen, alkyl, fluoroalkyl, formyl, alkoxycarbonyl, acyl, hydroxy, alkoxy, acyloxy, glycosyloxy, amino, alkylamino, mercapto, alkylthio and nitro; B represents a single bond or a straight chain alkylene group containing 1-4 carbon atoms which may have at least one substituent selected from the group consisting of alkyl, aryl, aralkyl, hydroxy and oxo; R represents an atom or a group selected from the group consisting of hydrogen, alkali metal, alkaline earth metal, alkyl, cycloalkyl, aralkyl and aryl; and n is 2 or 3, or its pharmaceutically acceptable salt is disclosed.
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- Rearrangements of cyclobutenones. Synthesis of benzoquinones from 4-alkenyl-4-hydroxycyclobutenones
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The rearrangement of 4-alkenyl-4-hydroxycyclobutenones to quinones and related aromatic compounds is described. This rearrangement is complimentary to the previously reported ring expansions of 4-aryl- and 4-alkynyl-4-hydroxycyclobutenones. The synthetic scope and utility of the reaction are discussed. It is employed as a key step in the synthesis of a number of benzoquinones as well as in the total synthesis of the natural product, (±)-O-methylperezone and its regioisomer, (±)-O-methylisoperezone as well as coenzyme Q0 and aurantiogliocladin.
- Perri, Steven T.,Moore, Harold W.
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p. 1897 - 1905
(2007/10/02)
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- Reductive Lactonization of Strategically Methylated Quinone Propionic Acid Esters and Amides
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It has been shown that the reduction of quinone propionic acid esters or amides bearing three methyl groups in the so-called "trialkyl lock" positions (o-, β-, β-positions) is accompanied by spontaneous lactonization with the release of alcohol or amine, respectively.A new convenient method is reported for introducing the β,β-dimethylpropionic acid side chain onto an appropriate hydroquinone nucleus via alkylative cyclization in methanesulfonic acid.Oxidation of the resulting lactone gives the quinone propionic acid, which can be converted by normal techniques to the corresponding ester or amide derivative.Initial model studies were carried out on pentamethylated systems 6 and 7.In order to make available quinones of varying redox potential or enhanced solubility in physiological media, methoxy- and amino-substituted quinones 10a, 10b, and 17a,b were synthesized.Upon reduction under mild conditions (Na2S2O4), all model esters or amides underwent reductive cyclization with loss of alcohol or amine.In the case of 7a the intermediate hydroquinone 19 could be isolated and its conversion to 4 with ejection of diethylamine followed by NMR techniques
- Carpino, Louis A.,Triolo, Salvatore A,Berglund, Richard A
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p. 3303 - 3310
(2007/10/02)
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