- Oxidation of 1,3,7-trimethylxanthine by hypochlorite ion
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The kinetics of the oxidative conversion of 1,3,7-trimethylxanthine upon treatment with hypochlorite ions (OCl-) in aqueous medium at 283-298 K and pH 8.2 was studied. The reaction order with respect to each component was determined and proved to be 1. It was established that the temperature dependence of the reaction rate follows the Arrhenius equation. The activation parameters of the reaction were measured: E a = 33.58 kJ/mol, ΔH ≠ = 31.12 kJ/mol, ΔS ≠ = -170.02 J/(K mol), ΔG ≠ = 81.45 kJ/mol. The stoichiometry of the reaction was studied, and the chemistry of the oxidative conversion of caffeine treated with OCl- is discussed.
- Kheidorov,Ershov,Chalyi,Titorovich
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Read Online
- The Absence of Nucleophilic Catalysis in the Nitrosation of Amides. Kinetics and Mechanism of the Nitrosation of Methylurea and the Reverse Reaction
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Rate constants have been determined for the nitrosation of methylurea (MU) in acid solution and also for the reverse reaction, the denitrosation of N-methyl-N-nitrosourea (MNU).The nitrosation reaction is essentially irreversible at the low acidities (0.01-0.4M-H2SO4) chosen for the experiments whereas the denitrosation reaction was examined at higher acidities (0.5-2.7M-H2SO4) in the presence of excess of hydrazine sulphate (a trap for free nitrous acid) when it is irreversible.For nitrosation the rate law, rate = k+> was established and there was no catalysis by substantial concentrations of added potassium bromide or potassium thiocyanate.Similarly the rate law for denitrosation was found to be rate = khA (where hA is the acidity function used for the protonation of amides), and again there was no catalysis by added potassium bromide, potassium thiocyanate,or thiourea.Te absence of nucleophilic catalysis in the nitrosation of amides had previously been noted and is a puzzling feature when comparison is made with the well established catalysis for amines.This is explained, together with the other observed results, by a detailed consideration of the individual kinetic steps involved in both reactions, and in particular by application of a limiting condition to both forward and reverse reactions in which the actual rate constant for the denitrosation process in an amide is very large compared with the proton transfer to the solvent from the intermediate.
- Hallett, Geoffrey,Williams, D. Lyn H.
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Read Online
- Oxyhalogen-sulfur chemistry: Bromate oxidation of 1-methyl-2-thiourea in acidic medium
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The reaction between bromate and 1-methyl-2-thiourea, CH3NH(NH2)C=S (MTU), has been studied in acidic medium. The stoichiometry of the reaction in excess MTU has been established as 4BrO3- + 3CH3NH-(NH2)C=S + 3H2O → 4Br- + 3SO42- + 3CH3NH(NH2)C=O + 6H+ (A); and in excess bromate the stoichiometry is: 8BrO3- + 5CH3NH(NH2)C=S + H2O → 4Br2 + 5SO42- + 5CH3NH(NH2)C=O + 2H+ (B). Stoichiometry B includes the oxidation of MTU (stoichiometry A) and the oxidation of Br- by the excess BrO3-: BrO3- + 5Br- + 6H+ → 3Br2 + 3H2O. In excess BrO3- the reaction is characterized by an induction period followed by formation of Br2. The reaction between Br2 and MTU is very fast with a bimolecular lower limit rate constant of 2.0 × 106 M-1 s-1 such that the formation of Br2 is an indicator for the complete consumption of MTU. The reaction could be followed by monitoring the depletion of MTU through its absorbance at λ = 239 nm or the formation of Br2 at λ = 390 nm. The rate of reaction was deduced as -d[BrO3-]/dt = k0[BrO3-][MTU][H+]2 with k0 = 14.7 ± 1.2 M-3 s-1. A proposed 17-step reaction mechanism gives good agreement between experimental data and computer simulations.
- Jonnalagadda, Sreekantha B.,Chinake, Cordelia R.,Simoyi, Reuben H.
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Read Online
- Regioselective Formal [3+2] Cycloadditions of Urea Substrates with Activated and Unactivated Olefins for Intermolecular Olefin Aminooxygenation
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A new class of intermolecular olefin aminooxygenation reaction is described. This reaction utilizes the classic halonium intermediate as a regio- and stereochemical template to accomplish the selective oxyamination of both activated and unactivated alkenes. Notably, urea chemical feedstock can be directly introduced as the N and O source and a simple iodide salt can be utilized as the catalyst. This formal [3+2] cycloaddition process provides a highly modular entry to a range of useful heterocyclic products with excellent selectivity and functional-group tolerance.
- Wu, Fan,Alom, Nur-E,Ariyarathna, Jeewani P.,Na?, Johannes,Li, Wei
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supporting information
p. 11676 - 11680
(2019/07/31)
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- Noncanonical RNA Nucleosides as Molecular Fossils of an Early Earth—Generation by Prebiotic Methylations and Carbamoylations
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The RNA-world hypothesis assumes that life on Earth started with small RNA molecules that catalyzed their own formation. Vital to this hypothesis is the need for prebiotic routes towards RNA. Contemporary RNA, however, is not only constructed from the four canonical nucleobases (A, C, G, and U), it also contains many chemically modified (noncanonical) bases. A still open question is whether these noncanonical bases were formed in parallel to the canonical bases (chemical origin) or later, when life demanded higher functional diversity (biological origin). Here we show that isocyanates in combination with sodium nitrite establish methylating and carbamoylating reactivity compatible with early Earth conditions. These reactions lead to the formation of methylated and amino acid modified nucleosides that are still extant. Our data provide a plausible scenario for the chemical origin of certain noncanonical bases, which suggests that they are fossils of an early Earth.
- Schneider, Christina,Becker, Sidney,Okamura, Hidenori,Crisp, Antony,Amatov, Tynchtyk,Stadlmeier, Michael,Carell, Thomas
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supporting information
p. 5943 - 5946
(2018/04/30)
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- Activation of 1-methyl-5-nitro-2-pyrimidinone by dearomatization using a secondary amine
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Electron-deficient 1-methyl-5-nitro-2-pyrimidinone is easily attacked by methanol or pyrrolidine to afford the corresponding adducts, respectively, by which aromaticity of nitropyrimidinone is lost. Indeed, the amine-adduct exhibited higher reactivity than that of original structure to facilitate the reaction with 1,3-dicarbonyl compound leading to diazabicyclic compound at room temperature. The amine-adduct also underwent the ring opening reaction to furnish nitroenamines with (Z)-configuration.
- Asahara, Haruyasu,Yasuoka, Azusa,Nishiwaki, Nagatoshi
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p. 253 - 259
(2019/04/27)
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- A practically simple, catalyst free and scalable synthesis of: N -substituted ureas in water
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A practically simple, mild and efficient method is developed for the synthesis of N-substituted ureas by nucleophilic addition of amines to potassium isocyanate in water without organic co-solvent. Using this methodology, a variety of N-substituted ureas (mono-, di- and cyclic-) were synthesized in good to excellent yields with high chemical purity by applying simple filtration or routine extraction procedures avoiding silica gel purification. The developed methodology was also found to be suitable for gram scale synthesis of molecules having commercial application in large volumes. The identified reaction conditions were found to promote a unique substrate selectivity from a mixture of two amines.
- Tiwari, Lata,Kumar, Varun,Kumar, Bhuvesh,Mahajan, Dinesh
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p. 21585 - 21595
(2018/06/26)
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- N, O - dimethyl - N - nitro-isourea preparation method
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The invention discloses a method for preparing N,O-dimethyl-N-nitroisourea by amination reaction, methylation reaction and nitration reaction. The equation is disclosed in the specification. The methyl urea obtained by the amination reaction and the monomethyl sulfate obtained by the methylation reaction can be directly used for the nitration reaction without purification. The cheap and accessible ammonia gas is used as the amination reagent in the amination reaction; in the nitration reaction, the sulfuric acid is used as a catalyst and a reaction solvent, thereby further lowering the raw material cost of the method; and the method has the advantages of mild technological conditions, wide raw material sources, lower production cost, high product quality and high content, and is easy to operate and suitable for industrial production.
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Paragraph 0030
(2017/08/24)
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- Synthesis of 6-azapurines by transformation of toxoflavins and reumycins (7-azapteridines) and their cytotoxicities
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This paper describes a reliable and facile synthesis of 6-azapurines, 1,5-dimethyl-1H-imidazo[4,5-e][1,2,4]triazin-6(5H)-ones and 5-methyl-5H-imidazo[4,5-e][1,2,4]triazin-6(7H)-ones, by treatment of toxoflavins and reumycins with 10% aqueous or ethanolic sodium hydroxide at 5-70°C or reflux, followed by decarboxylation and oxidation by air along with a benzilic acid type rearrangement. Furthermore, heating the produced 6-azapurines in 10% ethanolic sodium hydroxide afforded the corresponding 1-methyl-5,6-dioxo-1,4,5,6-tetrahydro-1,2,4-triazines with 1-methylurea. The antitumour activities of the 6-azapurines against CCRF-HSB-2 (human T-cell acute lymphoblastoid leukemia) and KB (human oral epidermoid carcinoma) cell lines were also investigated in vitro and some of the compounds showed prospective antitumour activities.
- Ma, Jun,Yoneda, Fumio,Nagamatsu, Tomohisa
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p. 203 - 210
(2015/02/19)
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- An improved method for the preparation of alkyl/arylurea derivatives using chlorocarbonylsulfenyl chloride as carbonylating agent
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A convenient procedure has been developed for preparation of aminesubstituted or monomethylamine-substituted alkyl/arylurea derivatives. The method comprises two steps-reaction of an alkyl/aryl amine with chlorocarbonylsulfenyl chloride in a non-polar solvent to produce an alkyl/arylcarbonylsulfenyl chloride, then reaction of this alkyl/ arylcarbonylsulfenyl chloride with ammonia or monomethylamine in a two-phase reaction with a phase-transfer catalyst, to produce the corresponding alkyl/aryl-substituted urea. Springer Science+Business Media B.V. 2012.
- Manidhar,K. Uma Maheswara Rao,C. Suresh Reddy,Ch. Syamasunder,Adeppa,Misra, Krishna
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p. 2479 - 2489
(2013/03/13)
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- Ionic liquid mediated one-pot synthesis of 6-aminouracils
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A novel, one-pot synthesis of 6-aminouracils via in situ generated ureas and cyanoacetylureas in the presence of an ionic liquid catalyst, 1,1,3,3-tetramethylguanidine acetate, is described. The catalyst can be recycled for five consecutive runs without loss of activity. The mechanism for the ring closure of cyanoacetylurea to 6-aminouracil is also discussed.
- Chavan, Sunil S.,Degani, Mariam S.
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supporting information; experimental part
p. 296 - 299
(2012/03/26)
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- PROCESS FOR STRAIGHTENING KERATIN FIBRES WITH A HEATING MEANS AND DENATURING AGENTS
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The invention relates to a process for straightening keratin fibres, comprising: (i) a step in which a straightening composition containing at least two denaturing agents is applied to the keratin fibres, (ii) a step in which the temperature of the keratin fibres is raised, using a heating means, to a temperature of between 110 and 250° C.
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- Preparation of mono-, di-, and trisubstituted ureas by carbonylation of aliphatic amines with S,S-dimethyl dithiocarbonate
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General procedures are reported to prepare N-alkylureas, N,N′-dialkylureas (both symmetrical and unsymmetrical), and N,N,N′-trialkylureas by carbonylation of aliphatic amines, employing S,S-dimethyl dithiocarbonate (DMDTC) as a phosgene substitute. All reactions were carried out in water. Symmetrical disubstituted ureas were prepared directly working at 60°C with a molar ratio of DMDTC:amine = 1:2, preferably under nitrogen. Unsymmetrical ureas were prepared in two steps via S-methyl N-alkyl-thiocarbamate intermediates, which are formed selectively in the first step at room temperature. These intermediates react in the second step with ammonia or various aliphatic amines, both primary and secondary, at temperatures varying between 50 and 70°C. All the target ureas were obtained in high yields (28 examples, average yield 94%) and with very high purity (generally >99.2%). Also to be noted is the recovery of a co-product of industrial interest, methanethiol, in an amount of two moles for each mole of DMDTC, with complete exploitation of the reagent. Georg Thieme Verlag Stuttgart.
- Artuso, Emma,Degani, Iacopo,Fochi, Rita,Magistris, Claudio
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p. 3497 - 3506
(2008/09/19)
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- Reaction of thiourea S,S-dioxides with dyes containing carbonyl or azo groups
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The kinetics of decomposition of thiourea and N-methylthiourea S,S-dioxides in alkaline aqueous medium and their reactions with oxygen, Indigo Carmine, and Acid Yellow 11 were studied. The decomposition of thiourea S,S-dioxides in weakly alkaline media was found to follow two pathways leading to the formation of ammonia and sulfoxylate ion, respectively. The second pathway predominates in strongly alkaline media. Thiourea S,S-dioxides can be used for selective reduction of azo compounds to the corresponding hydrazo derivatives. Nauka/Interperiodica 2006.
- Makarov,Kudrik,Davydov
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p. 1599 - 1603
(2008/02/07)
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- Facile desulfurization of thioamides and thioureas with tetrabutylammonium periodate under mild conditions
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Thioamides and thioureas were reacted with tetrabutylammonium periodate at room temperature to afford the corresponding amides and ureas, respectively, under aprotic conditions. Springer-Verlag 2005.
- Pourali, Ali Reza
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p. 733 - 737
(2007/10/03)
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- Process to prepare alkyl-ureas from O,S-dimethyl dithiocarbonate
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The present invention relates to the preparation of alkyl-ureas, starting from O,S-dimethyl dithiocarbonate, which provides the following steps: A) causing the O,S-dimethyl dithiocarbonate to react with a primary amine of general formula R1NH2in order to obtain an O-methyl thiocarbamate; B) isomerising the O-methyl thiocarbamate in order to obtain an S-methyl thiocarbamate; C) causing the S-methyl thiocarbamate with a compound of general formula R′R″NH, wherein R′ and R″ may be equal or different one in respect of the other and of R1and may be H, R2or R3, in order to obtain one of the alkyl-ureas of formula (4), (5) or (6).
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(2010/02/06)
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- Method for preparing crambescidin core acid intermediates and their use for preparing crambescidin alkaloid analogs as therapeutic agents
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The invention provides methods to synthesize zwitterionic pentacyclic crambescidin core intermediates having the carboxylate side chain in the natural axial orientation, and a range of crambescidin alkaloid analogs.
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- Process to prepare alkyl-ureas from O,S-dimethyl dithiocarbonate
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The present invention relates to the preparation of alkyl-ureas, starting from O,S-dimethyl dithiocarbonate, which provides the following steps:A) causing the O,S-dimethyl dithiocarbonate to react with a primary amine of general formula R1NH2 in order to obtain an O-methyl thiocarbamate;B) isomerising the O-methyl thiocarbamate in order to obtain an S-methyl thiocarbamate;C) causing the S-methyl thiocarbamate with a compound of general formula R'R"NH, wherein R' and R" may be equal or different one in respect of the other and of R1 and may be H, R2 or R3, in order to obtain one of the alkyl-ureas of formula (4), (5) or (6).
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- Flame-induced addition of urea to unsaturated carboxylic acids
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When a hydrogen-oxygen flame was blown against an aqueous solution of urea and maleic acid, N-carbamoylaspartic acid was generated. This compound seemed to be formed by the addition of an amidinoxyl radical to a C-C double bond of the acid, followed by a thermal rearrangement of an amidinoxy to a ureido group.
- Terasaki, Masanori,Nomoto, Shinya,Mita, Hajime,Shimoyama, Akira
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p. 855 - 856
(2007/10/03)
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- Oxidation chemistry of 3,7-dimethylxanthine - A central behavioural stimulant at solid electrodes
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The electrochemical oxidation of 3,7-dimethylxanthine has been studied in the pH range 2.1-10.7 at pyrolytic graphite, platinum and glassy carbon electrodes. The electrooxidation of 3,7-dimethylxanthine at solid electrodes proceeds in a single 4e, 4H+ pH dependent step to give a diimine species which decomposes in chemical followup steps. The UV absorbing intermediate generated during electrooxidation of 3,7-dimethylxanthine decayed approximately at the same rate as that of xanthine and followed the first order kinetics. The products of electrooxidation of 3,7-dimethylxanthine were characterized and a reaction scheme is suggested to explain their formation. The effect of introducing methyl groups into the electrooxidation of xanthine is also presented.
- Goyal, Rajendra N.,Rastogi, Arshi
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p. 495 - 509
(2007/10/03)
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- Voltammetric and chronoamperometric investigations on the oxidation of 7-methylxanthine
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Electrooxidation of 7-methylxanthine has been studied at pyrolytic graphite electrode in phosphate to be buffers of pH 2.0-10.9. A well defined 4e, 4H+ oxidation peak was noticed and an unstable diimine is formed whose half life has been found to be 40 ms by chronoamperometry. The reaction has been identified as EC in which charge transfer is followed by chemical reactions. The products have been characterized by m.p., 1HNMR and mass spectrum and a tentative reaction mechanism for their formation is suggested.
- Goyal, Rajendra N.,Singhal, Naveen K.
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- Kinetics of Oxidation of Caffeine by Bromamine-B in HCl Medium
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Kinetics of oxidation of caffeine by sodium N-bromobenzenesulphonamide (bromamine-B; BAB) in HCl medium have been studied at 288 K. The rate shows a first order dependence on [BAB], fractional orders in [H+] and [Cl-] and is independent of [caffeine]. Addition of the reaction product, benzenesulphonamide and variation of ionic strength of the medium have no effect on rate. A decrease of the dielectric constant of the medium decreased the rate constant. The solvent isotope effect has been studied in D2O medium. Activation parameters have been evaluated from the Arrhenius plots. Mechanisms proposed and the derived rate laws are in agreement with the observed kinetics.
- Puttaswamy,Mayanna
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- Liquid-phase process for preparing mono- and dimethylurea
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Kinetics of homogeneous liquid-phase reaction of urea with monomethylamine was studied by differentiation of the time dependence of the concentrations of the reaction products. Based on the results obtained, a unit for continuous synthesis of mono- and dimethylurea was developed.
- Bazanov,Berdichevskii,Bogorad,Datsevich,Mukhortov,Sokolova
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p. 2040 - 2042
(2007/10/03)
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- Piperidine, pyrrolidine and hexahydro-1H-azepines promote release of growth hormone
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The present invention is directed to certain novel compounds identified as substituted piperidines, pyrrolidines and hexahydro-1H-azepines of the general structural formula: STR1 wherein R1, R4, R5, A, X, Y and n are as defined herein. These compounds promote the release of growth hormone in humans and animals. This property can be utilized to promote the growth of food animals to render the production of edible meat products more efficient, and in humans, to treat physiological or medical conditions characterized by a deficiency in growth hormone secretion, such as short stature in growth hormone deficient children, and to treat medical conditions which are improved by growth hormone. Growth hormone releasing compositions containing such compounds as the active ingredient thereof are also disclosed.
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- Oxidation of caffeine by sodium N-bromo-p-toluene sulphonamide in HCl medium
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Kinetics of oxidation of caffeine by sodium N-bromo-p-toluenesulphonamide (BAT) in HCl medium has been studied at 288 K. The rate shows a first order dependence on [BAT], fractional orders in [H+] and [Cl-] and is independent of [caffeine]. Addition of the reaction product, p-toluenesulphonamide and varying ionic strength of the medium have no effect on the rate. The rate constant decreases with decrease in the dielectric constant of the medium. The solvent isotope effect has been studied in D2O medium. Activation parameters have been evaluated from the Arrhenius plots. The proposed reaction mechanism and the derived rate laws are consistent with the observed kinetics.
- Puttaswamy,Mayanna
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p. 225 - 227
(2007/10/03)
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- The mechanism of decomposition of N-methyl-N-nitrosourea (MNU) in water and a study of its reactions with 2'-deoxyguanosine, 2'-deoxyguanosine 5'-monophosphate and d(GTGCAC)
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The carcinogenicity of N-methyl-N-nitrosourea (MNU) arises, from its ability to methylate DNA, This occurs in an aqueous environment and therefore an appreciation of the mode of decomposition of MNU in water is essential to understanding the mechanism of DNA methylation and its base sequence dependence. The kinetics of MNU hydrolyses are shown to be first order in MNU with a steep rise in rate above pH 8. Using NMR for in situ monitoring of reaction intermediates and products from hydrolyses of [13CO]MNU, [15NH2]MNU and [13CH3]MNU, it is proved that base-induced hydrolysis of MNU is initiated by deprotonation at the carbamoyl group. The critical reactive species are shown to be the methyldiazonium ion (Me-N2+) and cyanate (NCO-). Investigations of reactions of [13CH3]MNU with 2'-deoxyguanosine (dGuo) and 2-deoxyguanosine 5'-monophosphate (dGuo-5P) showed that: a) the site of methylation of dGuo is highly pH-dependent (relatively more N-1 and O6-methylation compared to N-7 occurs at higher pH; b) the principal site of methylation of dGuo-5P by MNU is at phosphate; c) incorporation of deuterium into methyl groups occurs in D2O at higher pH. Methylation of the oligonucleotide d(GT[15N]GCAC) by MNU in D2O showed partial deuteriation of the N7-methyl groups of the guanines, whilst methylation by MNU in water indicated no significant preference for either guanine with respect to N7-methylation.
- Golding, Bernard T.,Bleasdale, Christine,McGinnis, Joseph,Mueller, Susanna,Rees, Hue Thu,Rees, Nicholas H.,Farmer, Peter B.,Watson, William P.
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p. 4063 - 4082
(2007/10/03)
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- Comparison of the Electrochemical and Enzymic Oxidation of 1,3,7-Trimethyluric Acid at Solid Electrodes
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The electrochemical oxidation of 1,3,7-trimethyluric acid has been studied in phosphate buffers in the pH range 2.1-10.2 at solid electrodes. In cyclic voltammetry a single, well defined, pH-dependent oxidation peak was obtained at all of the three electrodes used. However, the reduction behavior of the oxidation product was different at pyrolytic graphite, glassy carbon (GCE), and platinum due to adsorption at PGE and GCE. The nature of the electrode reaction was established as EC, in which a charge transfer is followed by competitive chemical reactions. The formation of the same UV-absorbing intermediate and products and identical rate constants for the decay of the UV-absorbing intermediate indicated that the electrochemical oxidation of 1,3,7-trimethyluric acid proceeds by an identical mechanism at PGE, GCE, and Pt. The results of a peroxidase-catalyzed oxidation of 1,3,7-trimethyluric acid were compared with the electrochemical oxidation; it is concluded that both of the oxidations follow a similar pathway.
- Goyal, Rajendra Nath,Jain, Ajay Kumar,Jain, Neena
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p. 1987 - 1995
(2007/10/03)
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- Piperidine, pyrrolidine and hexahydro-1H-azepines promote release of growth hormone
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The present invention is directed to certain novel compounds identified as substituted piperidines, pyrrolidines and hexahydro-1H-azepines of the general structural formula: STR1 wherein R1, R4, R5, A, X, Y and n are as defined herein. These compounds promote the release of growth hormone in humans and animals. This property can be utilized to promote the growth of food animals to render the production of edible meat products more efficient, and in humans, to treat physiological or medical conditions characterized by a deficiency in growth hormone secretion, such as short stature in growth hormone deficient children, and to treat medical conditions which are improved by the anabolic effects of growth hormone. Growth hormone releasing compositions containing such compounds as the active ingredient thereof are also disclosed.
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- Electrochemical and peroxidase catalysed oxidation of 1,7-dimethyluric acid and effect of methyl groups on the oxidation mechanism
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The electrochemical oxidation of 1,7-dimethyluric acid has been studied over a wide pH range of 2.2-10.3 at solid electrodes.Based on the results obtained from linear and cyclic sweep voltammetry, coulometry, spectroscopic studies and various analytical studies, a reaction mechanism has been proposed.The enzymatic oxidation of 1,7-dimethyluric acid has also been found to follow an identical pathway.The products of oxidation have been separated and characterized by using mp, 1H NMR and mass spectra.N-Methylation of the pyrimidine ring of purine causes protonation of nitrogen and affects the oxidation mechanism by not permitting the ring contraction of the diol intermediate.
- Goyal, Rajendra N.,Jain, Ajay K.,Jain, Neena
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p. 1153 - 1160
(2007/10/03)
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- Electrochemical and enzymic oxidation of 9-methyluric acid at solid electrodes
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The electrochemical oxidation of 9-methyluric acid has been studied in the pH range 2.0-11.3 at pyrolytic graphite, platinum and glassy carbon electrodes.The oxidation was found to occur in a single 2e-, H+ pH-dependent reaction at all the three electrodes.Adsorption complications were observed at the pyrolytic graphite and glassy carbon electrodes whereas no such behaviour was observed at platinum.The UV-spectral changes and the kinetics of the decay of the UV-absorbing intermediate generated during the reaction were found to be essentially the same at all the three electrodes.The peroxidase catalyzed oxidation of 9-methyluric acid was also found to be similar to the electrochemical oxidation.The products of oxidation were the same at all the electrodes suggesting thereby that adsorptive action at the surface of PGE and GCE did not affect the EC mechanism
- Goyal, Rajendra N.,Jain, Ajay K.,Jain, Neena
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p. 1055 - 1062
(2007/10/02)
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- Electrochemical and enzymatic oxidation of 7-methyluric acid
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The electrochemical oxidation of 7-methyluric acid has been studied in phosphate buffers (pH range 3.2-11.2) at pyrolytic graphite electrode.In linear and cyclic sweep voltammetry, 7-methyluric acid exhibited one well defined 2e, 2H(1+) pH dependent oxidation peak.The pseudo first order rate constants for the decay of UV absorbing intermediate have been calculated at different pH.At pH 3.2 products of electrooxidation were characterised to be alloxan and methyl urea whereas at pH 7.0 the major products of oxidation were found to be methylated allantoin and 1-methyl-5-hydroxyhydantoin-5-carboxamide.The enzymatic oxidation of 7-methyluric acid also indicated behaviour similar to electrochemical oxidation.Tentative EC mechanism for the oxidation has also been suggested.Key Words: purines / 7-methyluric acid / electrochemical oxidation
- Goyal, R. N.,Bansal, V.,Verma, M. S.
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p. 146 - 153
(2007/10/02)
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- Process for the preparation of asymmetrically substituted ureas
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Process for the preparation of asymmetrically substituted ureas by reaction of a gaseous mixture of isocyanic acid and ammonia having a temperature of 260° to 600° C. with a primary or secondary amine.
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- Substituted 1,3,5-triazinetriones, for use against parasitic protozoa
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Protecting against parasitic protozoa with substituted 1,3,5-triazinetriones of the formula STR1 in which R1 represents aromatic or heteroaromatic radicals, each of which is optionally substituted, R2 represents H, alkyl, alkenyl, alkinyl or aralkyl, each of which is optionally substituted, R3 represents one or more identical or different radicals from the group consisting of hydrogen, halogen, alkyl, halogenoalkyl, alkoxy, alkylthio, halogenoalkoxy, halogenoalkylthio, cyano, alkoxycarbonyl, alkylsulphonyl and halogenoalkylsulphonyl, R4 represents hydrogen, a straight-chain, branched or cyclic alkyl radical, alkenyl, alkinyl, aralkyl or aryl, each of which is optionally substituted, and R5 represents hydrogen, optionally substituted alkyl, alkenyl, alkinyl or aralkyl. Also novel intermediates therefor.
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- Electrochemical Behaviour of 9-Methylxanthine at Glassy Carbon Electrode
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The electrochemical oxidation of 9-methylxanthine at a glassy carbon electrode has been examined in the pH range 1.9 - 10.00 by linear and cyclic sweep voltammetry, coulometry and spectral studies.The products of electrooxidation have been identified and a plausible mechanism is suggested.
- Goyal, R. N.
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p. 343 - 347
(2007/10/02)
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- THE STRUCTURE OF THEOBROMURIC ACID
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The structure of theobromuric acid was revised and the correct 8a-hydroxy-1,2,3,4,6,7,8,8a-octahydro-1,7-dimethyl-2,4,6,8-tetraoxoimidazo -1,3,5-triazine (5a) formula was assigned on the basis of chemical and spectroscopic evidence.
- Poje, M.,Palkovic, A.
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p. 3173 - 3176
(2007/10/02)
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- Organic compounds substituted heptadeca-5,9- and 5,10-dienoic acid
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The present invention provides novel substituted heptadeca-5,9- and 5,10-dienoic acid and similar fatty acid compounds which are derivatives of certain prostaglandins and are potent thromboxane A2 inhibitors. By virtue of this pharmacological property, they represent useful pharmacological agents for a wide variety of purposes.
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- SYNTHESIS OF METHYL 3-(N'-ALKYLUREIDO)-2-METHYL-2-PROPENOATES AND THEIR CYCLIZATION TO 3-ALKYL-5-METHYLURACILS
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Stereoisomeric methyl 3-(N'-alkylureido)-2-methyl-2-propenoates (Ia-Id) were prepared by acid-catalyzed reaction of N-alkylureas (R = methyl, benzyl, isopropyl and tert-butyl) with methyl 3-methoxy-2-methyl-2-propenoate (III).Reaction of the ester III with N-tert-butylthiourea afforded the thioureides (E)-Ie and (Z)-Ie.On treatment with sodium methoxide in methanol, compounds Ia-Ic cyclized to the corresponding 3-alkyl-5-methyluracils IIa-IIc whereas compounds Id and Ie underwent only a base catalyzed E/Z isomerization with (E)-isomers predominating.
- Ledvina, Miroslav,Farkas, Jiri
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p. 676 - 688
(2007/10/02)
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- Reactions of Alkylnitrosoureas in Aqueous Solution
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The acid- and base-catalyzed decompositions of N-methyl-, N,N'-dimethyl-, and N,N',N'-trimethyl-N-nitrosourea in aqueous solution have been studied.Below pH 2, the N-methyl compound undergoes both denitrosation and hydrolysis.The denitrosation yields methylurea and nitrous acid.The hydrolysis yields largely methylamine, nitrogen, and carbon dioxide.The acid-catalyzed denitrosation and hydrolysis of the trimethylnitrosourea are somewhat more rapid than the corresponding reactions of N-methyl-N-nitrosourea.The denitrosation of this compound yields trimethylurea and nitrous acid.The hydrolysis yields methanol, dimethylamine, nitrogen, and carbon dioxide.The solvent isotope effect, kH2O / kD2O = 1.3, and the absence of chloride ion catalysis suggest that the denitrosation reaction proceeds by a rate-determining proton transfer which is followed by the rapid loss of the nitroso group.The results for the hydrolysis reaction are compatible with a formulation in which a hydrate of the nitrosourea is protonated in a rate-determining step to form a tetrahedral intermediate which subsequently decomposes to yield methyldiazonium hydroxide and a carbamic acid derivative.The base-catalyzed reactions of the mono-, di-, and trimethylnitrosoureas are first order in hydroxide ion over a broad pH range.The hydrolysis of N-methyl-N-nitrosourea yields methanol and derivatives of carbamic acid.Salt effects on the reaction rate are negligible except for the influence of lithium ion.The rate constants for the hydrolysis of the mono- and dimethyl compounds depend upon the buffer concentration at pH 9.5.These constants reach limiting values.The rate constants for the hydrolysis of the trimethyl compound alsodepend upon the buffer concentration, but a limiting value is not achieved.The solvent isotope effect for the base-catalyzed reaction, the exchange reaction of water-18O with the carbonyl group of the urea, and the fact that N-methyl-N-nitrosourea is hydrolyzed about 2.2104 times more rapidly than N,N',N'-trimethyl-N-nitrosourea suggest that the hydrolysis occurs by a mechanism in which a tetrahedral intermediate is formed.Often, the formation of this intermediate is rate limiting.However, under certain conditions, its decomposition to methyldiazonium hydroxide and a carbamate anion which decompose to form methanol and the other products may be rate determining.
- Snyder, John K.,Stock, Leon M.
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p. 1990 - 1999
(2007/10/02)
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