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Simple Reaction (simple + reaction)
Terms modified by Simple Reaction Selected AbstractsOxime Carbonates: Novel Reagents for the Introduction of Fmoc and Alloc Protecting Groups, Free of Side ReactionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2010Sherine N. Khattab Abstract Fmoc and Alloc protecting groups represent a consistent alternative to classical Boc protection in peptide chemistry. The former was established in the last decades as the ,-amino protecting group of choice, whereas the latter allows a fully orthogonal protection strategy with Fmoc and Boc. Usually, the introduction of the Fmoc and Alloc moieties takes place through their halogenoformates, azides, or activated carbonates. This rather simple reaction is accompanied by several side reactions, specially the formation of Fmoc/Alloc dipeptides and even tripeptides. The present work describes new promising Fmoc/Alloc-oxime reagents, which are easy to prepare, stable, and highly reactive crystalline materials that afford almost contaminant-free Fmoc/Alloc-amino acids in high yields by following a conventional procedure. Amongst the Fmoc-oxime derivatives, the N -hydroxypicolinimidoyl cyanide derivative (N -{[(9H-fluoren-9-yl)methoxy]carbonyloxy}picolinimidoyl cyanide) gave the best results for the preparation of Fmoc-Gly-OH, which is the most predisposed to give side reactions. The same Alloc-oxime analogue afforded the preparation of Alloc-Gly-OH in good yield, purity, and extremely low dipeptide formation, as analyzed by reverse-phase HPLC and NMR spectroscopy. [source] Synthesis of Enantiomerically Pure 2,3,4,6-Tetrasubstituted Tetrahydropyrans by Prins-Type Cyclization of Methyl Ricinoleate and Aldehydes,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2006Ursula Biermann Abstract The AlCl3 -catalyzed Prins-type cyclization of methyl ricinoleate (1), an enantiomerically pure renewable compound, with aldehydes such as heptanal (2a), isobutyraldehyde (2b), pivaldehyde (2c) and benzaldehyde (2d) is a simple reaction for the diastereoselective synthesis of enantiomerically pure 2,3,6-trialkyl-substituted 4-chlorotetrahydropyrans. The respective 4-hydroxytetrahydropyrans are obtained e.g. with aldehydes 2a and 2d using montmorillonite KSF/O as the catalyst. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] MEG reveals different contributions of somatomotor cortex and cerebellum to simple reaction time after temporally structured cuesHUMAN BRAIN MAPPING, Issue 7 2006Tim Martin Abstract Magnetoencephalography (MEG) was used to measure brain activity while participants performed a simple reaction to targets after either a random interval (uncued targets) or a series of isochronous warning stimuli with 200-ms intervals that acted as a countdown. Targets could arrive "on time" or "early" relative to the preceding warning stimuli. Cerebellar activity before any stimulus onset predicted uncued simple reaction time. Onset of activity in somatomotor cortex relative to the target predicted reaction time after two warning stimuli when the target arrived on time or early. After three warning stimuli, when the target arrived on time and was certain to occur, prestimulus cerebellar activity and somatomotor onset were significant predictors of reaction time. When the target arrived early after three warning stimuli, prestimulus cerebellar and cingulate activity were predictive. The cerebellar results may reflect a number of possible factors, including a role in timing, response readiness, prediction and attention. Hum. Brain Mapping 2005. © 2005 Wiley-Liss, Inc. [source] Evaluation of the cognitive, psychomotor and pharmacokinetic profiles of rupatadine, hydroxyzine and cetirizine, in combination with alcohol, in healthy volunteersHUMAN PSYCHOPHARMACOLOGY: CLINICAL AND EXPERIMENTAL, Issue 1 2006Manuel J. Barbanoj Abstract Introduction The Central Nervous System (CNS) impairment induced by moderate alcohol (ALC) ingestion may be enhanced if other drugs are taken simultaneously. Rupatadine (RUP) is a new H1 -antihistamine which also inhibits platelet activating factor (PAF) release in inflammatory reactions. Objective The main aim of the study was to assess the effects of ALC 0.8,g/Kg on RUP (10,mg and 20,mg) CNS effects. An evaluation of alcohol and RUP pharmacokinetics was also attained. Methods Eighteen healthy young volunteers of both sexes participated in a phase I, randomised, crossover, double-blind, placebo-controlled study. At 2-week intervals they received six treatments: (a) placebo (PLA), (b) ALC alone and ALC in combination with: (c) hydroxyzine 25,mg (HYD), (d) cetirizine 10,mg (CET), (e) RUP 10,mg or (f) RUP 20,mg. At baseline and several times thereafter, seven psychomotor performance tests (finger tapping, fine motoric skills, nystagmus, temporal estimation, critical-flicker-fusion frequency, ,d2' cancellation, simple reaction) and eleven subjective self-reports (drunkenness, sleepiness, alertness, clumsiness, anger, inattentiveness, efficiency, happiness, hostility, interest and extraversion) were carried out. Two-way (treatment, time) ANOVAs for repeated measures to each variable together with a multivariate non-parametric approach were applied. Plasma concentrations of alcohol, and of RUP and its metabolites, were quantified by validated immunofluorescence and LC/MS/MS methods, respectively. Plasma-time curves for all compounds were analysed by means of model-independent methods. Results The combination of alcohol with HYD, CET and RUP 20,mg produced more cognitive and psychomotor impairment as compared to alcohol alone, being the combination of alcohol and HYD the one which induced the greatest deterioration. The combination of alcohol and RUP 10,mg could not be differentiated from ALC alone. Subjective self-reports reflect effects on metacognition after the combination of alcohol with HYD and CET i.e. the increased objective impairment observed was not subjectively perceived by the subjects. No significant differences were obtained when comparing alcohol plasma concentrations assessed after the treatments evaluated. RUP showed a lineal kinetic relationship after 10 and 20,mg with a higher exposition to both metabolites assayed. Conclusions Present results showed that single oral doses of rupatadine 10,mg in combination with alcohol do not produce more cognitive and psychomotor impairment than alcohol alone. Higher doses of rupatadine, in combination with alcohol, may induce cognitive and psychomotor deterioration as hydroxyzine and cetirizine at therapeutic doses. Copyright © 2006 John Wiley & Sons, Ltd. [source] Hydrogeochemistry of seepage water collected within the Youngcheon diversion tunnel, Korea: source and evolution of SO4 -rich groundwater in sedimentary terrainHYDROLOGICAL PROCESSES, Issue 9 2001Gi-Tak Chae Abstract In the Youngcheon Diversion Tunnel area, South Korea, 46 samples of tunnel seepage water (TSW) and borehole groundwater were collected from areas with sedimentary rocks (mainly sandstone and shale) and were examined for hydrogeochemical characteristics. The measured SO4 concentrations range widely from 7·7 to 942·0 mg/l, and exceed the Korean Drinking Water Standard (200 mg/l) in about half the samples. The TDS (total dissolved solid) content generally is high (171,1461 mg/l) from more shale-rich formations and also reflects varying degrees of water,rock interaction. The water is classified into three groups: Ca SO4 type (61% of the samples collected), Ca SO4 HCO3 type (15%) and Ca HCO3 type (24%). The Ca HCO3 type water (mean concentrations=369 mg/l Ca, 148 mg/l HCO3 and 23 mg/l SO4) reflected the simple reaction between CO2 -recharged water and calcite, whereas the more SO4 -rich nature of Ca SO4 type water (mean concentrations=153 mg/l Ca, 66 mg/l HCO3 and 416 mg/l SO4) reflected the oxidation of pyrite in sedimentary rocks and fracture zones. Pyrite oxidation resulted in precipitation of amorphous iron hydroxide locally within the tunnel as well as in high concentrations of Ca (mean 153 mg/l) and Na (mean 49 mg/l) for TSW, and is associated with calcite dissolution resulting in pH buffering. The pyrite oxidation required for the formation of Ca SO4 type water was enhanced by the diffusion of oxygenated air through the fractures related to the tunnel's construction. The subsequent outgassing of CO2 into the tunnel resulted in precipitation of iron-bearing carbonate. Copyright © 2001 John Wiley & Sons, Ltd. [source] A Simple and Practical Method for the Preparation and Purity Determination of Halide-Free Imidazolium Ionic LiquidsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2006Claúdia Abstract The reaction of N -alkylimidazole with alkyl sulfonates at room temperature affords 1,3-dialkylimidazolium alkanesulfonates as crystalline solids in high yields. The alkanesulfonate anions can be easily substituted by a series of other anions [BF4, PF6, PF3(CF2CF3)3, CF3SO3 and N(CF3SO2)2] by simple reaction of anions, salts, or acids in water at room temperature. Extraction with dichloromethane, filtration through a short basic alumina column and solvent evaporation affords the desired ionic liquids in 80,95% yield. The purity (>99.4%) of these ionic liquids can be determined by 1H NMR spectra using the intensity of the 13C satellites of the imidazolium N -methyl group as internal standard. [source] Theoretical studies on the structure and protonation of Cu(II) complexes of a series of tripodal aliphatic tetraamines: Good correlations with the experimental dataJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2010Sadegh Salehzadeh Abstract DFT(B3LYP) studies on first protonation step of a series of Cu(II) complexes of some tripodal tetraamines with general formula N[(CH2)nNH2][(CH2)mNH2][(CH2)pNH2] (n = m = p = 2, tren; n = 3, m = p = 2, pee; n = m = 3, p = 2, ppe; n = m = 3, tpt; n = 2, m = 3, p = 4, epb; and n = m = 3, p = 4; ppb) are reported. First, the gas-phase proton macroaffinity of all latter complexes was calculated with considering following simple reaction: [Cu(L)]2+(g) + H+(g) , [Cu(HL)]3+(g). The results showed that there is a good correlation between the calculated proton macroaffinities of all complexes with their stability constants in solution. Then, we tried to determine the possible reliable structures for microspecies involved in protonation process of above complexes. The results showed that, similar to the solid state, the [Cu(L)(H2O)]2+ and [Cu(HL)(H2O)2]3+ are most stable species for latter complexes and their protonated form, respectively, at gas phase. We found that there are acceptable correlations between the formation constants of above complexes with both the , and , of following reaction: [Cu(L)(H2O)]2+(g) + H+(g) + H2O(g) , [Cu(HL)(H2O)2]3+(g). The , of the latter reaction can be defined as a theoretically solvent,proton macroaffinity of reactant complexes because they have gained one proton and one molecule of the solvent. The unknown formation constant of [Cu(epb)]2+ complex was also predicted from the observed correlations. In addition, the first proton affinity of all complexes was studied in solution using DPCM and CPCM methods. It was shown that there is an acceptable correlation between the solvent,proton affinities of [Cu(L)(H2O)]2+ complexes with formation constants of [Cu(HL)(H2O)2]3+ complexes in solution. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Emergence of homochirality in far-from-equilibrium systems: Mechanisms and role in prebiotic chemistryCHIRALITY, Issue 8 2007Raphaël Plasson Abstract Since the model proposed by Frank (Frank FC, Biochem Biophys Acta 1953;11:459,463), several alternative models have been developed to explain how an asymmetric non-racemic steady state can be reached by a chirally symmetric chemical reactive system. This paper explains how a stable non-racemic regime can be obtained as a symmetry breaking occurring in a far-from-equilibrium reactive system initiated with an initial imbalance. Departing from the variations around the original Frank's model that are commonly described in the literature, i.e. open-flow systems of direct autocatalytic reactions, we discuss recent developments emphasizing both an active recycling of components and an autocatalytic network of simple reactions. We will present our APED model as the most natural realization of such thermodynamic openness and non-equilibrium, of recycling and of network autocatalysis, each of these in prebiotic conditions. The different experimental and theoretical models in the literature will be classified according to mechanism. The place and role of such self-structured networks responsible for the presence of homochirality in the primitive Earth will be detailed. Chirality 19:589,600, 2007 © 2007 Wiley-Liss, Inc. [source] | ||||||||||