- Relative contribution of rat cytochrome P450 isoforms to the metabolism of caffeine: The pathway and concentration dependence
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The aim of the present study was to estimate the relative contribution of rat P450 isoforms to the metabolism of caffeine and to assess the usefulness of caffeine as a marker substance for estimating the activity of P450 in rat liver and its potential for
- Kot, Marta,Daniel, Wladyslawa A.
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- The relative contribution of human cytochrome P450 isoforms to the four caffeine oxidation pathways: An in vitro comparative study with cDNA-expressed P450s including CYP2C isoforms
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The aim of the present study was to estimate the relative contribution of cytochrome P450 isoforms (P450s), including P450s of the CYP2C subfamily, to the metabolism of caffeine in human liver. The experiments were carried out in vitro using cDNA-expresse
- Kot, Marta,Daniel, Wladyslawa A.
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- Absorption spectra of isomeric OH adducts of 1,3,7-trimethylxanthine
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The reactions of OH?, O?-, and SO4?- with 1,3,7-trimethylxanthine (caffeine) were studied by pulse radiolysis with optical and conductance detection techniques. The absorption spectra of transients formed in OH? reaction in neutral solutions exhibited peaks at 310 and 335 nm, as well as a broad absorption maximum at 500 nm, which decayed by first-order kinetics. The rate (k = (4.0 ± 0.5) × 104 s-1) of this decay is independent of pH in the range 4-9 and is in agreement with that determined from the conductance detection (k = 4 × 104 s-1). The spectrum in acidic solutions has only a broad peak around 330 nm with no absorption in the higher wavelength region. The intermediates formed in reaction of O?- absorb around 310 and at 500 nm, and the first-order decay at the latter wavelength was not seen. The OH radical adds to C-4 (X-4OH?) and C-8 (X-80H?) positions of caffeine in the ratio 1:2 as determined from the redox titration and conductivity measurements. H abstraction from the methyl group is an additional reaction channel in O?- reaction. Dehydroxylation of the X-4OH? adduct occurs, whereas the X-8OH? adduct does not undergo ring opening. The rate constant for addition of O2 to X-4OH? is estimated to be ～1 x 109 M-1 s-1, whereas it is unreactive toward X-8OH?. The spectrum obtained for OH? reaction in oxygenated solutions is similar to that observed in SO4?- reaction in basic solutions. The radical cation of caffeine formed from its reaction with SO4?- (λmax = 320-340 nm) is hydrolyzed in basic solutions to yield the X-8OH? adduct. The molar absorptivities of the X-8OH? and the X-4OH? adducts at 300 and 335 nm are 6500 and 5300 M-1 cm-1, respectively. The yield of 1,3,7-trimethyluric acid in OH? reaction in the absence of O2 (28%) is reduced by more than 50% in its presence. The differences in the mechanism of OH? reaction with caffeine and its isomer 1,3,9-trimethylxanthine (isocaffeine) are discussed.
- Vinchurkar,Rao,Mohan,Mittal,Schmidt,Jonah
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- Br?nsted acid catalysis in the oxidation of purine based alkaloids by Mn(VII) in aqueous acetonitrile and sodium fluoride medium: A kinetic approach
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Br?nsted acid (HClO4, H2SO4) catalyzed Mn(VII) oxidation of purine alkaloids such as caffeine, theophylline and theobromine in aqueous acetonitrile and sodium fluoride medium revealed first order kinetics in both [(Mn(VII)] and [Alkaloid] at constant acidity and temperature. Sodium fluoride was added to the reaction mixture in order to avoid/suppress auto catalytic reaction due to the generation of Mn(III) and Mn(IV) species during the course of Mn(VII) oxidations in acidic solutions. An increase in the Br?nsted acids (HClO4, H2SO4) concentration accelerated the rate of oxidation. Rate enhancements observed here in are analyzed by Zucker-Hammett, Bunnett and Bunnett-Olsen criteria of acidity functions. On the basis of observed Bunnett-Olsen criteria of acidity functions, the most plausible mechanism has been proposed with the involvement of water molecule in the slow step (as proton transferring agent).
- Ramakrishna Reddy,Muddam, Bhooshan,Sambashiva Rao,Rajanna,Panasa Reddy,Thirumala Chary
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p. 1051 - 1057
(2021/05/10)
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- Kinetic insights on the oxidation of acetaminophen and caffeine by a Mn(IV)3 complex
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The kinetics of the oxidation reactions of APAP and Cafn by a Mn(IV)-oxidant, [MnIV3(μ-O)4(phen)4(H2O)2]4+ (1) has been studied at room temperature. Under the acidic reaction condition ([H+] = 0.2–1.0?M), both APAP and Cafn exist in equilibrium with their conjugate acids APAPH+ and CafnH+ and each of the species acts as the potential reductants. Kinetic observations reveal that the observed rate constant, ko, values increase with the increase in media acidity and the ionic strength, I. The second-order rate-constant values for oxidizing the protonated forms of the two reductants (APAPH+ and CafnH+) were evaluated to be 6.04 ± 0.29 and 0.18 ± 0.01?M?1?s?1, respectively. Overall, under acid media, Mn(IV)-complex efficiently oxidizes APAP to a mixture of benzoquinone and acetamide (or, to quinone oxime and acetic acid) and Cafn to 1,3,7-trimethyluric acid.
- Das, Ranendu Sekhar,Singh, Bula
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p. 565 - 573
(2021/09/09)
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- Preparation methods of three kinds of methyl uric acid compounds, intermediate and preparation method of the intermediate
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The invention provides preparation methods of three types of compounds which can be extracted from plants such as tea trees and have the effects of resisting depression, tranquilizing and hypnosis, resisting inflammation and easing pain, reducing stress damage of the liver cells and improving the exercise ability, an intermediate and a preparation method of the intermediate. The method is simple and convenient to operate, high in safety, high in atom economy and less in three wastes, and the raw and auxiliary materials are cheap and easy to obtain, low in toxicity, safe and stable; the reaction conditions are mild, the impurities are few, and the yield is high. The product is purified by crystallization, column chromatography is avoided, the operation is simple and feasible, and the process is stable, easy to control and convenient in reaction after-treatment, and can be economically and conveniently used for industrial production.
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- Room-temperature copper-catalyzed oxidation of electron-deficient arenes and heteroarenes using air
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No pressure: The oxidation of aromatic C-H bonds at room temperature was realized through a copper-catalyzed "oxygenase-type" oxidation of arenes and heteroarenes in the presence of air (see scheme). The reaction involves an oxygen-atom transfer from O2 in the air onto the substrates. Copyright
- Liu, Qiang,Wu, Pan,Yang, Yuhong,Zeng, Ziqi,Liu, Jie,Yi, Hong,Lei, Aiwen
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supporting information; experimental part
p. 4666 - 4670
(2012/06/30)
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- Photooxidation of substituted purines in presence of peroxydisulphate in aqueous solution
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Photooxidation of purine bases, viz., caffeine, theobromine, theophylline, xanthine, hypoxanthine, adenine and guanine in aqueous solution has been carried out in presence of peroxydisulphate (PDS). Peroxydisulphate is activated to SO4.- at 254 nm. The reactions are followed by measuring the absorbance of purine bases at their respective γmax]. The rates of reactions are calculated under different experimental conditions. The light intensity is measured using peroxydisulphate solution as standard chemical actinometer. Using reaction rate and light intensity at 254 nm, the quantum yields are calculated. The rates of photooxidation of purine bases are found to increase with increase in [PDS] and independent of [purine]. The increase of light intensity has been found to increase the rate of oxidation. The quantum yields are found to depend on [purine] but independent of [PDS] and light intensity. On the basis of experimental results a probable mechanism is suggested in which peroxydisulphate on photolysis gives sulphate radical anion which initiates the reaction by capturing an electron from C8 position of purine to form purine radical cation. This radical cation deprotonates and undergoes further oxidation to give C(8) hydroxy purine.
- Swaraga, Midudhula Sudha,Adinarayana, Mundra
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p. 2096 - 2100
(2007/10/03)
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- Highly efficient C-8 oxidation of substituted xanthines with substitution at the 1-, 3-, and 7- Positions using biocatalysts
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A bacterial consortium consisting of strains belonging to the genus Klebsiella and Rhodococcus quantitatively converts 1-, 3- and 7-substituted xanthines to their respective 8-oxo compounds.
- Madyastha,Sridhar
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p. 677 - 680
(2007/10/03)
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- Mechanism of free radical oxidation of caffeine in aqueous solution
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The oxidation of caffeine with persulfate and hydroxyl radicals in aqueous solution has been studied by EPR spectroscopy and HPLC analysis. In both cases the formation of 1,3,7-trimethyluric acid is observed as the main final product. A C8-OH radical adduct is postulated as the intermediate after reaction with OH., and leads to the final product after further oxidation. This radical is too short-lived to be observed by EPR After oxidation of caffeine with SO4.- its radical cation is detected by EPR. This radical reacts with water to produce the above mentioned C8-OH radical adduct after deprotonation. In the presence of dibasic phosphate a spectrum attributed to the C8-phosphate radical adduct is observed. This radical results from the nucleophilic attack of the buffer on the radical cation of caffeine. Hydrolysis and oxidation of the phosphate radical intermediate results in the formation of 1,3,7-trimethyluric acid.
- Telo, Joao P.,Vieira, Abel J. S. C.
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p. 1755 - 1757
(2007/10/03)
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- Purines. XIV [1]. Synthesis and properties of 8-nitroxanthine and its N- methyl derivatives
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Xanthine (1) and its N-methyl derivatives 2-16 have been nitrated to the corresponding 8-nitro derivatives 17-32 under different reaction conditions. Nitration in glacial acetic acid with nitric acid works well with the N-7 unsubstituted and some of the 9-methylxanthines, respectively, whereas the 7- methylxanthine derivatives react best with nitronium tetrafluoroborate in sulfolane or glacial acetic acid. The 8-nitro group can be displaced nucleophilically to form 8-chloro-, 33, 34, 8-ethoxy-, 35, 36, and uric acid derivatives 37-40, respectively. The newly synthesized 8-nitroxanthines have been characterized by elemental analyses, pK-determinations and uv and 1H- nmr spectra.
- Mosselhi,Pfleiderer
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p. 1221 - 1228
(2007/10/02)
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- ADDITION OF ELECTROPHILIC RADICALS TO CAFFEINE: SYNTHETIC ASPECTS AND INFLUENCE OF THE PEROXIDIC INITIATORS
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Primary and secondary electrophilic radicals such as: .CHRCO2CH3 (R=H, CH3, CO2CH3) and tertiary .CCl3 radical were added directly at C-8 of, th model purine compound, caffeine to give the corresponding 8-substituted derivatives in fairly good yields.Unexpected reaction of caffeine with oxy radicals from the initiators (PhCO2., t-BuOO.) gave rise to C-5 substituted 1,3,7-trimethyl-5,7-dihydrouric acid derivatives (C-5-R=CCl3, CH3, C(CH3)2CO2CH3) and to the spirodihydantoin C-8 adduct derivative of caffeine 11.
- Zylber, J.,Ouazzani-Chahdi, L.,Lefort, D.,Chiaroni, A.,Riche, C.
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p. 721 - 732
(2007/10/02)
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