- Pseudosymmetry in 2,5-dimethyl-1,4-benzenediol
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The title compound, C8H10O2, was prepared from di-acetyl by a high temperature and pressure reaction. Pseudosymmetry in the structure results in diffraction symmetry enhancement for half the reflections and the possibility of twinning and stacking faults. The structure consists of two independent but pseudosymmetrically-related P21/c substructures, each having centrosymmetric molecules on centres of inversion which are strongly hydrogen bonded to symmetry-related molecules to form layers perpendicular to c*, The structure may be described as an occupancy modulation, ordering a disordered parent structure in Pnma symmetry to form, upon change of axes, the P21c structure reported. The hydroxyl H atoms have two site options corresponding to alternative hydrogen-bonding patterns and the methyl H atoms in one substructure are rotationally disordered.
- Gainsford,Miller,Yorke,Rae
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Read Online
- Magnetic Resonance Studies of Cation Radicals from Chromans
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N.m.r. spectroscopy has been used to study the electron-exchange reaction between the substrate-radical pairs of 2,3,4,7,8,9-hexahydro-2,2,5,7,7,10-hexamethylbenzodipyran, 2,3,4,5,6,7-hexahydro-2,2,7,7,9,10-hexamethylbenzodipyran and 2,3,6,7-tetrahydro-2,2,4,6,6,8-hexamethylbenzodifuran and their cation radicals.The rate constants and energetics of activation of the reactions have been determined, along with absolute signs of the averaged proton hyperfine coupling constants.ENDOR and TRIPLE measurements provided accurate values of the individual coupling constants and their relative signs: the n.mr. and ENDOR data taken together gaved complete assignment.
- Smith, Ian M.,Sutcliffe, Leslie H.,Wiesner, Stefan,Lubitz, Wolfgang,Kurreck, Harry
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Read Online
- Aqueous solubility of organic compounds for flow battery applications: Symmetry and counter ion design to avoid low-solubility polymorphs
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Flow batteries can play an important role as energy storage media in future electricity grids. Organic compounds, based on abundant elements, are appealing alternatives as redox couples for redox flow batteries. The straightforward scalability, the independence of material sources, and the potentially attractive price motivate researchers to investigate this technological area. Four different benzyl-morpholino hydroquinone derivatives were synthesized as potential redox active species. Compounds bearing central symmetry were shown to be about an order of magnitude less soluble in water than isomers without central symmetry. Counter ions also affected solubility. Perchlorate, chlorate, sulfate and phosphate anions were investigated as counter ions. The formations of different polymorphs was observed, showing that their solubility is not a function of their structure. The kinetics of the transformation can give misleading solubility values according to Ostwald’s rule. The unpredictability of both the kinetics and the thermodynamics of the formation of polymorphs is a danger for new organic compounds designed for flow battery applications.
- Bereczki, Laura,Garcia, Sergio Navarro,Kónya, Dénes,Yang, Xian
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- Reduction of Activated Alkenes by PIII/PV Redox Cycling Catalysis
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The carbon–carbon double bond of unsaturated carbonyl compounds was readily reduced by using a phosphetane oxide catalyst in the presence of a simple organosilane as the terminal reductant and water as the hydrogen source. Quantitative hydrogenation was observed when 1.0 mol % of a methyl-substituted phosphetane oxide was employed as the catalyst. The procedure is highly selective towards activated double bonds, tolerating a variety of functional groups that are usually prone to reduction. In total, 25 alkenes and two alkynes were hydrogenated to the corresponding alkanes in excellent yields of up to 99 %. Notably, less active poly(methylhydrosiloxane) could also be utilized as the terminal reductant. Mechanistic investigations revealed the phosphane as the catalyst resting state and a protonation/deprotonation sequence as the crucial step in the catalytic cycle.
- Longwitz, Lars,Werner, Thomas
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supporting information
p. 2760 - 2763
(2020/02/05)
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- Can Donor Ligands Make Pd(OAc)2a Stronger Oxidant? Access to Elusive Palladium(II) Reduction Potentials and Effects of Ancillary Ligands via Palladium(II)/Hydroquinone Redox Equilibria
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Palladium(II)-catalyzed oxidation reactions represent an important class of methods for selective modification and functionalization of organic molecules. This field has benefitted greatly from the discovery of ancillary ligands that expand the scope, reactivity, and selectivity in these reactions; however, ancillary ligands also commonly poison these reactions. The different influences of ligands in these reactions remain poorly understood. For example, over the 60-year history of this field, the PdII/0 redox potentials for catalytically relevant Pd complexes have never been determined. Here, we report the unexpected discovery of (L)PdII(OAc)2-mediated oxidation of hydroquinones, the microscopic reverse of quinone-mediated oxidation of Pd0 commonly employed in PdII-catalyzed oxidation reactions. Analysis of redox equilibria arising from the reaction of (L)Pd(OAc)2 and hydroquinones (L = bathocuproine, 4,5-diazafluoren-9-one), generating reduced (L)Pd species and benzoquinones, provides the basis for determination of (L)PdII(OAc)2 reduction potentials. Experimental results are complemented by density functional theory calculations to show how a series of nitrogen-based ligands modulate the (L)PdII(OAc)2 reduction potential, thereby tuning the ability of PdII to serve as an effective oxidant of organic molecules in catalytic reactions.
- Bruns, David L.,Musaev, Djamaladdin G.,Stahl, Shannon S.
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supporting information
p. 19678 - 19688
(2020/12/18)
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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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- A Quencher-Fluorophore-Type Probe for Detection and Imaging of NADPH in Human Breast Cancer Cells
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A new fluorogenic trimethyl lock quinone (TLQ) derivative, designated as the quencher-TLQ-fluorophore-type probe (Q-TLQ-F), was developed for selective detection of nicotinamide adenine dinucleotide phosphate (NADPH). By taking advantage of the well-known facile intramolecular ring cyclization reaction (δ-lactonization) of TLQ that can release a reporter molecule upon reduction, Q-TLQ-F was successfully applied for the detection of physiological NADPH generated by glucose-6-phosphate dehydrogenase in human breast cancer MDA-MB-231 cells.
- Yu, Geunhyeok,Kim, Sungryung,Bae, Se Won,Yeo, Woon-Seok
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supporting information
p. 807 - 811
(2019/08/12)
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- Reactivity of iPrPCPIrH4 with para-benzoquinones
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In the interest of investigating new hydrogen acceptors for pincer–iridium catalyzed dehydrogenations with the ability to be catalytically recycled, a series of para-benzoquinones have been reacted with iPrPCPIrH4 in various solvents and conditions. Preliminary results indicate that a wide range of quinones are capable of dehydrogenating iPrPCPIrH4, and that several turn-overs in alcohol dehydrogenation by iPrPCPIr are possible at room temperature using benzoquinone acceptors. However, strong acceptor–catalyst interactions are inhibitory toward catalysis when the acceptor is used in excess. A new class of (bis)-η2 pi-adducts, formed between iPrPCPIr and benzoquinones, nicknamed “barber-chairs”, has been identified and 3 examples have been characterized.
- Wilklow-Marnell, Miles,Brennessel, William W.,Jones, William D.
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p. 209 - 214
(2017/11/24)
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- Metabolism of the Strobilurin Fungicide Mandestrobin in Wheat
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The metabolic fate of a new fungicide, mandestrobin, labeled with 14C at the phenoxy or benzyl ring was examined in wheat after a single spray application at 300 g/ha. Mandestrobin penetrated into foliage over time, with both radiolabels showing similar 14C distribution in wheat, and 2.8-3.3% of the total radioactive residue remained on the surface of straw at the final harvest. In foliage, mandestrobin primarily underwent mono-oxidation at the phenoxy ring to produce 4-hydroxy or 2-/5-hydroxymethyl derivatives, followed by their subsequent formation of malonylglucose conjugates. In grain, the cleavage of its benzyl phenyl ether bond was the major metabolic reaction, releasing the corresponding alcohol derivative, while the counterpart 2,5-dimethylphenol was not detected. The constant RS enantiomeric ratio of mandestrobin showed its enantioselective metabolism to be unlikely on/in wheat.
- Ando, Daisuke,Fujisawa, Takuo,Katagi, Toshiyuki
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p. 10154 - 10162
(2018/10/02)
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- One-Pot Synthesis to Quinone-Based Diaza[3.3]cyclophanes
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A simple one-pot synthesis to [3.3]cyclophanes that involves quinone moieties was found. The protocol tolerates a variety of amines that include aliphatic and aromatic structures with different functional groups, such as hydroxy groups, amides, and terminal double and triple bonds. The straightforward synthesis can be performed by a twofold N-alkylation reaction with 2,5-bis(bromomethyl)-3,6-dimethyl-1,4-benzoquinone (1). Neither anhydrous nor inert conditions are required. Various amines can be employed without any activating groups, several functionalities at end groups are tolerated, and the cyclophanes generated can be easily modified or embedded into larger molecular architectures. The redox-active nature of these cyclophanes allows their use in electron-transfer processes.
- Stahlhofen, Jana Marie,Schollmeyer, Dieter,Waldvogel, Siegfried R.
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p. 7226 - 7230
(2017/10/18)
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- ELECTROCHEMICALLY ACTIVE AGENTS FOR PH MODULATION IN BIOLOGICAL BUFFERS
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Device and methods for use in a biosensor comprising a multisite array of test sites, the device and methods being useful for modulating the binding interactions between a (biomolecular) probe or detection agent and an analyte of interest by modulating the pH or ionic gradient near the electrodes in such biosensor. An electrochemically active agent comprising quinone derivatives that is suitable for use in biological buffers for changing the pH of the biological buffers. Method for changing the pH of biological buffers using the electrochemically active agents. The methods of modulating the binding interactions provided in a biosensor, analytic methods for more accurately controlling and measuring the pH or ionic gradient near the electrodes in such biosensor, and analytic methods for more accurately measuring an analyte of interest in a biological sample.
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Paragraph 00299
(2017/01/26)
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- A General Strategy for Visible-Light Decaging Based on the Quinone Trimethyl Lock
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Visible-light triggered quinone trimethyl locks are reported as a general design for long-wavelength photoremovable protecting groups for alcohols and amines. Intramolecular photoreduction unmasks a reactive phenol that undergoes fast lactonization to release alcohols and amines. Model substrates are released in quantitative yield along with well-defined, colorless hydroquinone byproducts. Substituent modifications of the quinone core allow absorption from 400 to 600 nm.
- Walton, David P.,Dougherty, Dennis A.
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supporting information
p. 4655 - 4658
(2017/04/10)
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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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- Catalytic activity of Fe-porphyrins grafted on multiwalled carbon nanotubes in the heterogeneous oxidation of sulfides and degradation of phenols in water
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A biomimetic heterogeneous catalyst was prepared by immobilization of meso-tetrakis(4-carboxyphenyl)porphyrinatoiron(III) chloride (Fe(TCPP)Cl) on multiwalled carbon nanotubes (MWCNTs). The anchored catalyst was characterized by transmission electron microscopy, powder X-ray diffraction, ultraviolet–visible, and Fourier transform infrared spectroscopy. The amount of Fe-porphyrin loaded on the nanotubes was estimated by atomic absorption spectroscopy The thermogravimetric analysis demonstrated that the catalyst was thermally stable up to almost 350 °C, exhibiting high thermal stability. Oxidation of sulfides and phenols with urea hydrogen peroxide (UHP) in water was efficiently enhanced with excellent selectivity under the influence of [Fe(TCPP)Cl@MWCNT]. The title heterogeneous catalytic system facilitates a greener reaction because the reaction solvent is water and UHP is used as a safe oxidant.
- Rayati, Saeed,Nejabat, Fatemeh
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p. 967 - 974
(2017/09/26)
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- COMPOUNDS AND METHODS FOR ASSAYING REDOX STATE OF METABOLICALLY ACTIVE CELLS AND METHODS FOR MEASURING NAD(P)/NAD(P)H
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The present invention provides compounds and methods for assaying redox state of metabolically active cells and methods for assaying enzyme activity and/or metabolite level by coupling to redox defining co-factor NAD(P)/NAD(P)H measurement.
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Paragraph 00170
(2013/03/28)
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- Electrochemical "switching" of Si(100) modular assemblies
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We report on a modular approach for producing well-defined and electrochemically switchable surfaces on Si(100). The switching of these surfaces is shown to change a Si(100) surface from resistant to cell adsorption to promoting cell adhesion. The electrochemical conversion of the modified electrode surface is demonstrated by X-ray photoelectron spectroscopy, X-ray reflectometry, contact angle and cell adhesion studies.
- Ciampi, Simone,James, Michael,Le Saux, Guillaume,Gaus, Katharina,Justin Gooding
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supporting information; experimental part
p. 844 - 847
(2012/03/07)
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- Induction of molecular chirality by circularly polarized light in cyclic azobenzene with a photoswitchable benzene rotor
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New phototriggered molecular machines based on cyclic azobenzene were synthesized in which a 2,5-dimethoxy, 2,5-dimethyl, 2,5-difluorine or unsubstituted-1,4-dioxybenzene rotating unit and a photoisomerizable 3,3′-dioxyazobenzene moiety are bridged together by fixed bismethylene spacers. Depending upon substitution on the benzene moiety and on the E/Z conformation of the azobenzene unit, these molecules suffer various degrees of restriction on the free rotation of the benzene rotor. The rotation of the substituted benzene rotor within the cyclic azobenzene cavity imparts planar chirality to the molecules. Cyclic azobenzene 1, with methoxy groups at both the 2- and 5-positions of the benzene rotor, was so conformationally restricted that free rotation of the rotor was prevented in both the E and Z isomers and the respective planar chiral enantiomers were resolved. In contrast, compound 2, with 2,5-dimethylbenzene as the rotor, demonstrated the property of a light-controlled molecular brake, whereby rotation of the 2,5-dimethylbenzene moiety is completely stopped in the E isomer (brake ON, rotation OFF), while the rotation is allowed in the Z isomer (brake OFF, rotation ON). The cyclic azobenzene 3, with fluorine substitution on the benzene rotor, was in the brake OFF state regardless of E/Z photoisomerization of the azobenzene moiety. More interestingly, for the first time, we demonstrated the induction of molecular chirality in a simple monocyclic azobenzene by circular-polarized light. The key characteristics of cyclic azobenzene 2, that is, stability of the chiral structure in the E isomer, fast racemization in the Z isomer, and the circular dichroism of enantiomers of both E and Z isomers, resulted in a simple reversible enantio-differentiating photoisomerization directly between the E enantiomers. Upon exposure to r- or l-circularly polarized light at 488 nm, partial enrichment of the (S)- or (R)-enantiomers of 2 was observed. Copyright
- Hashim,Thomas, Reji,Tamaoki, Nobuyuki
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supporting information; experimental part
p. 7304 - 7312
(2011/08/05)
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- A straightforward hetero-diels-alder approach to (2-ambo,4′R, 8′R)-α/β/γ/δ-4-thiatocopherol
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A simple and original inverse electron demand hetero-Diels-Alder reaction has been successfully applied to the synthesis of (2-ambo,4′R,8′R)- α/β/γ/δ-4-thiatocopherol. Commercially available methyl hydroquinones and. (2E,7R,11R)-(+)-phytol were exploited for the preparation of the ortho-thioquinones, acting as electron-poor dienes, and of the proper 1,3-diene used as dienophile, respectively. The benzoxathiine cycloadducts, with the required tocopherol-like skeleton, were obtained with complete control, of regio and chemoselectivity. The antioxidant activity of 4-thiatocopherols was measured and rationalized in comparison with that of the corresponding natural components of Vitamin E.
- Menichetti, Stefano,Amorati, Riccardo,Bartolozzi, Maria Grazia,Pedulli, Gian Franco,Salvini, Antonella,Viglianisi, Caterina
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supporting information; experimental part
p. 2218 - 2225
(2010/07/03)
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- PREPARATION COMPRISING CHROMAN-2-ONE DERIVATIVES
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The invention relates to preparations comprising at least one compound of the formula (I), where the substituents R1 to R4 have a meaning indicated in claim 1, and salts and solvates thereof, and to the use thereof and selected compounds of the formula (I).
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Page/Page column 13
(2010/12/18)
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- Control of the regio- and stereoselectivity in Diels-Alder reactions with quinone boronic acids
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(Chemical Equation Presented) It all adds up: The dienophilic reactivity of 2-methyl-substituted quinones has been substantially increased by the introduction of a boronic acid substituent, which makes them equivalent to a highly reactive quinone. The Diels-Alder reactions of these quinones are followed by spontaneous and stereoselective protodeboronation to give the trans-fused adducts. The boron group is a temporal regiocontroller and leads to the uncommon meta adduct.
- Redondo, Maria C.,Veguillas, Marcos,Ribagorda, Maria,Carreno, M. Carmen
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supporting information; experimental part
p. 370 - 374
(2009/04/14)
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- C-D-glucopyranosyl derivatives of tocopherols - Synthesis and evaluation as amphiphilic antioxidants
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Treatment of dimethylhydroquinone dimethyl ethers (ortho and meta isomers) with glycopyranose pentaacetates (D-gluco, D-galacto) in the presence of SnCl4 and F3CCO2Ag selectively afforded the corresponding C-β-D-glycosyl derivatives by aromatic electrophilic substitution. Oxidation of the dimethoxybenzene moiety with ceric ammonium nitrate delivered C-β-D-glycosyl-dimethylbenzoquinones, which were reduced with Na2S2O4 to the corresponding C-β-D-glycosyldimethylhydroquinones. ZnCl2-catalyzed cyclization either with methylbut-2-en-1-ol (prenyl alcohol) or with all-racemic phytol led to acetyl-protected C-β-D-glycosyl chromanols or C-β-D-glycosyl tocopherols, the sugar residues of which were deacetylated under base catalysis conditions. These new molecules were evaluated as antioxidants in terms of their ability to inhibit the peroxidation of linoleic acid in SDS micelles. The position of the C-glucosyl moiety on the phenolic nucleus emerges as the critical structural determinant of their activity. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- He, Li,Galland, Stephanie,Dufour, Claire,Chen, Guo-Rong,Dangles, Olivier,Fenet, Bernard,Praly, Jean-Pierre
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experimental part
p. 1869 - 1883
(2009/04/04)
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- Vitamin E chemistry. Nitration of non-α-tocopherols: Products and mechanistic considerations
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(Chemical Equation Presented) In contrast to the α-form permethylated at the aromatic ring, non-α-tocopherols possess free aromatic ring positions which enable them to act as potent scavengers of electrophiles in vivo and in vitro. In preparation of enzymatic studies involving peroxynitrite and other nitrating systems, the behavior of non-α-tocopherols under nitration conditions was studied. The nitration products of β-, γ-, and δ-tocopherol were identified, comprehensively analytically characterized, and their structure was supported by X-ray crystal structure analysis on truncated model compounds. Even under more drastic nitration conditions, no erosion of the stereochemistry at 2-C occurred. The nitrosation of γ-tocopherol and δ-tocopherol was re-examined, showing the slow oxidation of the initial nitroso products to the corresponding nitro derivatives by air to be superimposed by a fast equilibrium with the tautomeric ortho-quinone monoxime, which only in the case of γ-tocopherol released hydroxyl amine at elevated temperatures to afford the stable ortho-quinone. Mononitration of δ-tocopherol selectively proceeded at position 5. This selectivity can be explained by the theory of strain-induced bond localization (SIBL) to the quinoid nitration intermediates. Bisnitration was only insignificantly disfavored by the first nitro group, so that under normal nitration conditions offering an excess of nitrating species only the bisnitration product was found.
- Patel, Anjan,Liebner, Falk,Netscher, Thomas,Mereiter, Kurt,Rosenau, Thomas
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p. 6504 - 6512
(2008/02/10)
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- OXAZOLE AND THIAZOLE PPAR MODULATORS
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The invention provides compounds (I) pharmaceutical compositions comprising such compounds and methods of using such compounds to treat or prevent diseases or disorders associated with the activity of the Peroxisome Proliferator-Activated Receptor (PPAR) families, particularly the activity of PPARδ.
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Page/Page column 27-28
(2010/11/27)
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- COMPOUNDS AND COMPOSITIONS AS PPAR MODULATORS
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The invention provides compounds, pharmaceutical compositions comprising such compounds and methods of using such compounds to treat or prevent diseases or disorders associated with the activity of the Peroxisome Proliferator-Activated Receptor (PPAR) families.
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Page/Page column 60
(2008/06/13)
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- COMPOUNDS AND COMPOSITIONS AS PPAR MODULATORS
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The invention provides compounds, pharmaceutical compositions comprising such compounds and methods of using such compounds to treat or prevent diseases or disorders associated with the activity of the Peroxisome Proliferator-Activated Receptor (PPAR) families.
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Page/Page column 48
(2010/11/27)
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- Preparation of 1,4-hydrobenzoquinones by the PCC/SiO2-promoted double oxidation of 3-cyclohexene-1,2-diols
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The PCC/SiO2-promoted double oxidation of 3-cyclohexene-1,2- diols, which were easily prepared by the two-step sequence of α-hydroxylation of various conjugated cyclohexenones and the subsequent nucleophilic carbonyl addition of alkyl anions, produced diversely substituted 1,4-hydrobenzoquinones. The Royal Society of Chemistry 2005.
- Kim, Hee Jin,Koo, Sangho
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p. 3479 - 3481
(2007/10/03)
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- Photoprocesses of p-Benzoquinones in Aqueous Solution
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The photochemistry of 1,4-benzoquinone (BQ) and several derivatives, for example, duroquinone, trimethyl-2,5- or 2,6-dimethyl-, and methyl-BQ in aqueous solution or mixtures with polar media, for example, acetonitrile or 2,2,2-trifluoroethanol, was studied by time-resolved UV-vis spectroscopy after pulses at 248 and 308 nm. The triplet state and the semiquinone radical (?QH/Q?-) of BQs are spectroscopically and kinetically separated intermediates. The radical yield in the absence of H-atom donors is low and significantly increased in the presence of alcohols. Efficient photoinduced charge formation, because of Q?- and H+ after H-atom transfer from 2-propanol to the triplet state, and small effects in the absence of a donor were observed by transient conductivity. The quantum yield of photodecomposition, λirr = 254 nm, is substantial for BQ, MeBQ, and Me2BQs in aqueous solution, but small for Me 4BQ. To account for the efficient photoconversion of BQs into hydrobenzoquinones and 2-hydroxy-1,4-benzoquinones, a novel water-mediated reaction not involving free radicals is proposed as major step. This mechanism is consistent with the prediction that the observed triplet state is monomeric and the yield of Q?-, detected by both transient absorption and conductivity, is low for sub-millimolar BQ, MeBQ, and Me2BQs at pH 5-6. In addition, H-atom abstraction from a polar organic solvent or by self-quenching plays a role in mixtures with water or at enhanced quinone concentration, respectively.
- Goerner, Helmut
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p. 11587 - 11595
(2007/10/03)
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- Chemistry of L-ascorbic acid. Part 3.1 Photoreduction of quinones with 5,6-O-isopropylidene-L-ascorbic acid
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Upon irradiation with UV light, instead of undergoing the Paterno-Buechi reaction, 5,6-O-isopropyIidene-L-ascorbic acid reduced quinones quite efficiently and rapidly to the corresponding hydroquinones. The Royal Society of Chemistry 2000.
- Kulkarni, Mukund G.,Kate, Sandesh D.
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p. 4242 - 4244
(2007/10/03)
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- A redox-sensitive resin linker for the solid phase synthesis of C- terminal modified peptides
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With the rapid development of combinatorial chemistry using solid phase synthesis, there is a great deal of interest in developing new solid phase linkers, which are stable during the solid phase synthesis process and yet readily cleavable under mild conditions. By taking advantage of a 'trimethyl lock'-facilitated lactonization reaction, we have developed a redox-sensitive resin linker for the synthesis of C-terminal-modified peptides. The cleavage only requires mild reducing agents such as sodium hydrosulfite, which is not expected to cause any problem with the commonly seen organic functional groups. Using this new linker, three short peptides were synthesized with high isolated yields (70-90%). Such a linker could potentially be used for the synthesis of modified peptide libraries, which allows for the ready cleavage of the linker under mild conditions.
- Zheng, Ailian,Shan, Daxian,Wang, Binghe
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p. 156 - 161
(2007/10/03)
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- Synthesis of quinones from hydroquinone dimethyl ethers. Oxidative demethylation with cobalt(III) fluoride
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The oxidative demethylation of 1,4-dimethoxynaphthalene and 1,4- dimethoxybenzene derivatives with cobalt(III) fluoride proceeded in good to excellent yield to afford the corresponding naphthoquinone and benzoquinone derivatives.
- Tomatsu, Ayumi,Takemura, Syunji,Hashimoto, Kimiko,Nakata, Masaya
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p. 1474 - 1476
(2007/10/03)
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- Comparative pulse radiolysis studies of alkyl- and methoxy-substituted semiquinones formed from quinones and hydroquinones
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Absorption spectra and rate constants for the disproportionate of 12 alkyl- and methoxy-substituted semiquinone anion free radicals (Q?-) produced by the one-electron reduction (using CO2?- as a reductant) of 1,4-benzoquinones and 1,4-naphthoquinone (Q) as well the oxidation (using N3? as an oxidant) of the corresponding hydroquinones (QH2) were determined by pulse radiolysis in 50 mM sodium phosphate buffer, pH 7.40 at room temperature. Both spectral and kinetic characteristics of Q?- only moderately depended on whether Q?- was produced from Q or QH2. Spectra of benzosemiquinones display two peaks with maximum at 310-320 nm and ca. 430 nm with the ratio of about 2-2.5. Molar absorption coefficients were determined. Rate constants for Q?- disproportionation (2k1) were correlated with the nature of substituents. While 2k1 was scarcely affected by methyl substitution, Q?- containing isopropyl, tert-butyl and methoxy substituents were visibly more stable than non-substituted and methyl-substituted Q?-.
- Roginsky, Vitaly A.,Pisarenko, Leonid M.,Bors, Wolf,Michel, Christa,Saran, Manfred
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p. 1835 - 1840
(2007/10/03)
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- Solid-State Photochemistry of the Mixed Crystals between Benzoquinones and Polymethylbenzenes
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Nine mixed crystals combined 1,4-benzoquinone (1), 2,5-xyloquinone (2) and duroquinone (3) with durene (a), pentamethylbenzene (b) and hexamethylbenzene (c) were prepared by a melting-resolidifying process and characterized by powder X-ray diffractometry, DSC and IR.Only the mixed crystal of 3 and a formed a 2:1 novel molecular crystal (4); other eight mixed crystals were simple polycrystalline mixtures of the two components.Irradiation of the molecular crystal 4 (3/a) and the mixed crystals 1/a, 1/b and 3/b caused intermolecular hydrogen abstraction to give hydroquinones and in some cases adducts.Product selectivities in the solid state were different from those in solution.Correlation between the crystal structure and the reactivity of 4 is discussed.
- Koshima, Hideko,Chisaka, Yosuke,Wang, Yang,Yao, Xinkan,Wang, Honggen,et al.
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p. 13617 - 13630
(2007/10/02)
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- Solid-state Reactivity of Crystalline Hydroquinones with Quinone Vapour; Crystal Structures of 2,5-Dimethylhydroquinone and 2,3,5,6-Tetramethylhydroquinone
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Use of single crystals of 2,5-dimethylhydroquinone and 2,3,5,6-tetramethylhydroquinone in studies of their reactions with 1,4-benzoquionone vapour has been found to give information not obtainable from previous studies of reaction powders.Structures of the two crystalline hydroquinones were determined by X-ray analysis.Crystals of the dimethylhydroquinone are orthorhombic, a = 13.256(2), b = 4.5609(8), c = 11.977(2) Angstroem, Z = 4, space group Pca21; and the structure has been refined to an R factor of 0.0335 on 704 non-zero reflections.Molecules have an anti-arrangement of hydroxy groups and form hydrogen-bonded chains with a motif like that of γ-hydroquinone.Slight differences in the geometry of the hydrogen bonding at the two ends of the molecule are responsible for the polar nature of the structure.Results of both the test for second harmonic generation and a pyroelectric test for non-centrosymmetry are positive with these crystals.The pyroelectric test applied to crystals in which twinning is known to occur shows clear evidence of such twinning and might be useful in certain other cases as a test for twinning.Crystals of the tetramethylhydroquinone are monoclinic, a = 8.317(3), b = 4.728(2), c = 13.514(5) Angstroem, β = 125.85(2) deg, Z = 2, space group P21/c; the structure has been refined to an R factor of 0.0367 on 813 non-zero reflections.Microscopic studies show evidence that the reaction is initiated at nucleation sites on reactive faces and that both quinone and hydroquinone molecules migrate during reaction.The faster reaction occurs at those faces where hydroxy groups emerge.It has been found that the shapes of the OH stretching regions of the Fourier transform i.r. spectra of these and other hydroquinones as well as the positions of the absorption maxima provide structural evidence useful for distinguishing among these compounds, and can be correlated with their crystal structures.
- Pennington, W. T.,Patil, A. O.,Paul, I. C.,Curtin, D. Y.
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p. 557 - 564
(2007/10/02)
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- Mechanism of the Oxidation of NADH by Quinones. Energetics of One-Electron and Hydride Routes
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The kinetics of NADH oxidation by 7 o-benzoquinones and 14 p-benzoquinones were studied by using buffered aqueous solutions and UV/vis spectroscopy.For each quinone the rate law was first order in NADH and first order in quinone.The rate constants varied from 0.0745 to 9220 M-1s-1.Variation of the pH from 6 to 8 gave no change in rate.The use of 4-D and 4,4-D2NADH revealed kinetic isotope effects.The dideutero data gave kH/kD in the range 1.6-3.1 for p-quinones and 4.2 for 3,5-di-tert-butyl-o-quinone.When p-quinones were used, the log k was a linear function of Eo for the quinone/hydroquinone monoanion (Q/QH(1-)) couple with a slope of 16.9 V-1. o-Quinones reacted about 100 times more rapidly, but the same linear relationship with a slope of 16.4 V-1 was observed.Comparisons to data for one-electron-transfer reactions indicate that such mechanisms are not involved.A hydride-transfer mechanism accommodates all the data, and rate-limiting hydrogen atom transfer followed by electron transfer cannot be ruled out.
- Carlson, Brian W.,Miller, Larry L.
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p. 479 - 485
(2007/10/02)
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- Magnetic Field Effects on the Photolysis of p-Benzoquinone Derivatives in Sodium Dodecyl Sulfate Micelles
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Magnetic field effects on the photochemical reactions of p-benzoquinone derivatives were studied in sodium dodecyl sulfate (SDS) micellar solutions by steady-state and nanosecond laser flash photolysis.The relative quantum yield of the disappearance of quinones by steady irradiation decreases with increasing magnetic field up to 250-350 G and then reaches a constant value.In the leser flash photolysis, the decay of a transient due to the semiquinone radicals in micellar solution consists of "fast " and "slow" decay components (ca. 100 ns and 50-100 μs), the intensity ratio of which decreases by 20-40percent with a magnetic field of 400-1000 G.The triplet - singlet intersystem crossing (isc) of a 2,5-dimethyl-p-benzosemiquinone - dodecyl sulfate ion radical pair is 2.6*106 and 1.0*106 s-1 at 0 and 950 G, respectively.The results are discussed in terms of the radical-pair model in which the triplet - singlet intersystem crossing of radical pairs is influenced by the external magnetic field.
- Tanimoto, Yoshifumi,Udagawa, Hiroko,Katsuda, Yoshihide,Itoh, Michiya
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p. 3976 - 3982
(2007/10/02)
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- REACTIONS OF ORGANOLITHIUM REAGENTS WITH p-BENZOQUINONES AND CYCLOHEXADIENONS, SYNTHESIS OF 4-ALKYL-4-HYDROXYCYCLOHEXA-2,5-DIEN-1-ONES AND 1,4-DIALKYLCYCLOHEXA-2,5-DIENE-1,4-DIOLS.
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Addition of organolithium reagents to p-benzoquinones in ether gives the corresponding 4-alkyl-4-hydroxycyclohexa-2,5-dien-1-ones.Addition of excess of the reagent to the p-benzoquinones, or to the 4-alkyl-4-hydroxycyclohexa-3,5-dien-1-ones, in tetrahydrofuran, gives the corresponding dialkylcyclohexa-2,5-diene-1,4-diols.
- Fischer, A.,Henderson, N.
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p. 701 - 704
(2007/10/02)
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- Process for preparing dihydric phenol derivatives
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A process for preparing dihydric phenol derivatives by oxidizing monohydric phenol derivatives with hydrogen peroxide in the presence of a ketone. This reaction can be promoted in the presence of sulfuric acid or a salt thereof or a sulfonic acid or a salt thereof.
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