- Biotransformation of 12C- and 2-13C-labeled methyl tert-butyl ether, ethyl tert-butyl ether, and tert-butyl alcohol in rats: Identification of metabolites in urine by 13C nuclear magnetic resonance and gas chromatography/mass spectrometry
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The biotransformation of the fuel oxygenates methyl tert-butyl ether (MTBE) and ethyl tertbutyl ether (ETBE) was studied in rats after inhalation exposure; the biotransformation of the initial metabolite of these ethers, tert-butyl alcohol, was studied after oral gavage. To study ether metabolism, rats were exposed for 6 h to initial concentrations of 2000 ppm of MTBE or ETBE, respectively [2-13C]MTBE and [2-13C]ETBE. Urine was collected for 48 h after the end of the exposure, and urinary metabolites were identified by 13C NMR (13C-labeled ethers) and gas chromatography/mass spectrometry (GC/MS) (12C- and 13C-labeled ethers). To study tert-butyl alcohol metabolism, rats were dosed either with tert-butyl alcohol at natural carbon isotope ratio or with 13C-enriched tert-butyl alcohol (250 mg/kg of body weight), urine was collected, and metabolites were identified by NMR and GC/MS. tert-Butyl alcohol was identified as a minor product of the biotransformation of MTBE and ETBE. In addition, small amounts of a tert- butyl alcohol conjugate, likely a glucuronide, were present in the urine of the treated animals. Moreover, the mass spectra obtained indicate the presence of small amounts of [13C]acetone in the urine of [13C]MTBE and [13C]ETBE-treated rats. 2-Methyl-1,2-propanediol, 2-hydroxyisobutyrate, and another unidentified conjugate of tert-butyl alcohol, most probably a surf ate, were major urinary metabolites of MTBE and ETBE as judged by the intensities of the NMR signals. In [13C]-tert-butyl alcohol-dosed rats, [13C]acetone, tert-butyl alcohol, and its glucuronide represented minor metabolites; as with the ethers, 2-methyl-1,2-propanediol, 2- hydroxyisobutyrate, and the presumed tert-butyl alcohol sulfate were the major metabolites present. In one human individual given 5 mg/kg [13C]- tert-butyl alcohol orally, 2-methyl-1,2-propanediol and 2-hydroxyisobutyrate were major metabolites in urine detected by 13C NMR analysis. Unconjugated tert-butyl alcohol and tert-butyl alcohol glucuronide were present as minor metabolites, and traces of the presumed tert-butyl alcohol sulfate were also present. Our results suggest that tert-butyl alcohol formed from MTBE and ETBE is intensively metabolized by further oxidation reactions. Studies to elucidate mechanisms of toxicity for these ethers to the kidney need to consider potential toxicities induced by these metabolites.
- Bernauer, Ulrike,Amberg, Alexander,Scheutzow, Dieter,Dekant, Wolfgang
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Read Online
- An Estimate of the Lifetime of 1,4-Dioxybutane Biradicals
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Previous kinetic data for the thermolysis of 1,2-dioxetanes has suggested a biradical or biradicaloid decomposition route, but direct evidence for a biradical intermediate has been lacking.We now report the trapping of a 1,4-dioxybutane biradical in the thermolysis of 3,3-dimethyl-1,2-dioxethane, where the lifetime is estimated to be in the range of 30-75 ps.Attempts to trap biradicals from the thermolysis of trimethyl- and tetramethyl-1,2-dioxethane were used unsuccessful, and it was estimated that the maximum lifetimes of these biradicals were 7 ps.
- Richardson, William H.,Lovett, Merylyn B.,Olson, Leif
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Read Online
- The discovery of a potent and selective pyrazolo-[2,3-e]-[1,2,4]-triazine cannabinoid type 2 receptor agonist
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The development of selective CB2 receptor agonists is a promising therapeutic approach for the treatment of inflammatory diseases, without CB1 receptor mediated psychoactive side effects. Preliminary structure-activity relationship studies on pyrazoylidene benzamide agonists revealed the -ylidene benzamide moiety was crucial for functional activity at the CB2 receptor. A small library of compounds with varying linkage moieties between the pyrazole and substituted phenyl group has culminated in the discovery of a potent and selective pyrazolo-[2,3-e]-[1,2,4]-triazine agonist 19 (CB2R EC50 = 19 nM, CB1R EC50 > 10 μM). Docking studies have revealed key structural features of the linkage group that are important for potent functional activity.
- Moir, Michael,Lane, Samuel,Montgomery, Andrew P.,Hibbs, David,Connor, Mark,Kassiou, Michael
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- Mo–Catalyzed One-Pot Synthesis of N-Polyheterocycles from Nitroarenes and Glycols with Recycling of the Waste Reduction Byproduct. Substituent-Tuned Photophysical Properties
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A catalytic domino reduction–imine formation–intramolecular cyclization–oxidation for the general synthesis of a wide variety of biologically relevant N-polyheterocycles, such as quinoxaline- and quinoline-fused derivatives, and phenanthridines, is reported. A simple, easily available, and environmentally friendly dioxomolybdenum(VI) complex has proven to be a highly efficient and versatile catalyst for transforming a broad range of starting nitroarenes involving several redox processes. Not only is this a sustainable, step-economical as well as air- and moisture-tolerant method, but also it is worth highlighting that the waste byproduct generated in the first step of the sequence is recycled and incorporated in the final target molecule, improving the overall synthetic efficiency. Moreover, selected indoloquinoxalines have been photophysically characterized in cyclohexane and toluene with exceptional fluorescence quantum yields above 0.7 for the alkyl derivatives.
- Hernández-Ruiz, Raquel,Rubio-Presa, Rubén,Suárez-Pantiga, Samuel,Pedrosa, María R.,Fernández-Rodríguez, Manuel A.,Tapia, M. José,Sanz, Roberto
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supporting information
p. 13613 - 13623
(2021/08/23)
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- KIF18A INHIBITORS
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Compounds of formula (I): (I), as defined herein, and synthetic intermediates thereof, which are capable of modulating KIF18A protein thereby influencing the process of cell cycle and cell proliferation to treat cancer and cancer-related diseases. The invention also includes pharmaceutical compositions, including the compounds, and methods of treating disease states related to the activity of KIF18A.
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Paragraph 0283
(2020/07/14)
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- Transfer hydrogenation of cyclic carbonates and polycarbonate to methanol and diols by iron pincer catalysts
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Herein, we report the first example on the use of an earth-abundant metal complex as the catalyst for the transfer hydrogenation of cyclic carbonates to methanol and diols. The advantage of this method is the use of isopropanol as the hydrogen source, thus avoiding the handling of flammable hydrogen under high pressure. The reaction offers an indirect route for the reduction of CO2 to methanol. In addition, poly(propylene carbonate) was converted to methanol and propylene glycol. This methodology can be considered as an attractive opportunity for the chemical recycling of polycarbonates.
- Liu, Xin,De Vries, Johannes G.,Werner, Thomas
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p. 5248 - 5255
(2019/10/11)
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- Synthesis, Characterization and Catalytic Application of Pyridine-Bridged N-Heterocyclic Carbene–Ruthenium Complexes in the Hydrogenation of Carbonates
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A series of bulky pyridine-bridged NHC–Ru complexes have been rationally designed and synthesized; these exhibited very high catalytic activity in the hydrogenation of cyclic and linear carbonates under mild reaction conditions. In the presence of catalytic amounts of a weak base, a broad range of substrates with different ring size and steric bulk were well tolerated, providing methanol and the corresponding diols in excellent yields with a catalyst loading as low as 0.5 mol %.
- Chen, Jiangbo,Zhu, Haibo,Chen, Jinjin,Le, Zhang-Gao,Tu, Tao
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supporting information
p. 2809 - 2812
(2017/10/23)
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- A Highly Regioselective Palladium-Catalyzed O,S Rearrangement of Cyclic Thiocarbonates
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This work describes an operationally simple catalytic synthesis of cyclic S-thiocarbonates with predictable regioselectivity in good yields. The reaction utilizes substrates derived from ubiquitous 1,2-diols in an atom economical intramolecular rearrangement, catalysed by an inexpensive and simple catalyst–ligand system. A crystal structure is presented that clearly confirms the regioselectivity of the reaction.
- Mahy, William,Cabezas-Hayes, Sinéad,Kociok-K?hn, Gabriele,Frost, Christopher G.
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supporting information
p. 6441 - 6444
(2017/11/13)
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- Quinoline or quinazoline derivatives, its preparation process and its use in medicine
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The invention relates to a quinoline or quinazoline derivative, its preparation method and an application in medicines, specifically to new quinoline or quinazoline derivative as shown in a general formula (I) and its medicinal salt or a pharmaceutical composition containing the derivative and a preparation method thereof. The invention further relates to an application of the quinoline or quinazoline derivative and its medicinal salt or the pharmaceutical composition containing the derivative in the preparation of a therapeutic agent, especially a protein kinase inhibitor. Each substituent group in the general formula (I) has the same definition as in the specification.
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Paragraph 0262-0266
(2018/01/19)
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- Dehydrochlorination of 2-chloroethanol, 2-chloro-1-propanol, 1-chloro-2-propanol, 2-chloro-2-methyl-1-propanol and 1-chloro-2-methyl-2- propanol
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The reactions between a few 1,2-chlorohydrins and sodium hydroxide have been studied and shown to involve a two-step nucleophilic elimination of hydrogen chloride. The data are given for the slow rate-determining step of 2-chloroethanol 1, 2-chloro-1-propanol 2, 1-chloro-2- propanol 3, 2-chloro-2-methyl-1-propanol 4 and 1-chloro-2-methyl-2-propanol 5. Compounds 4 and 5 gave 2-methyl-1,2-propanediol as the final product instead of oxiranes given by compounds 13. In contrast to some earlier reports the mere water reaction was shown to be almost negligible. In constant ionic strength the base concentration had no effect on the rates whereas at different base concentrations (0.0500.250 mol dm-3) alone the rate of alkaline dehydrochlorination of 1 clearly decreased (103k2, dm 3 mol-1 s-1: 10.0-8.7, respectively). The rate of 2 at constant base concentration (0.010 mol dm-3) and at different ionic strengths (dm3 mol-1: 0.010-0.500) decreased also (103k2, dm3 mol-1 s-1: 76-65, respectively) indicating that the decrease is mainly due to the change in the ionic strength also in the former case. ARKAT-USA, Inc.
- Pihlaja, Kalevi,Kiuru, Marja-Leena,Sippola, Anne
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p. 120 - 133
(2013/09/24)
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- Catalytic hydrogenation of cyclic carbonates: A practical approach from CO2 and epoxides to methanol and diols
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As an economical, safe and renewable carbon resource, CO2 turns out to be an attractive C1 building block for making organic chemicals, materials, and carbohydrates.[1] From the viewpoint of synthetic chemistry,[2] the utilization of CO2 as a feedstock for the production of industrial products may be an option for the recycling of carbon.[3] On the other hand, the transformation of chemically stable CO2 represents a grand challenge in exploring new concepts and opportunities for the academic and industrial development of catalytic processes.[4] The catalytic hydrogenation of CO2 to produce liquid fuels such as formic acid (HCO 2H)[5] or methanol[6] is a promising solution to emerging global energy problems. Methanol, in particular, is not only one of the most versatile and popular chemical commodities in the world, with an estimated global demand of around 48 million metric tons in 2010, but is also considered as the key to weaning the world off oil in the future.[6e, f] Although the production of methanol has already been industrialized by the hydrogenation of CO with a copper/zinc-based heterogeneous catalyst at high temperatures (250-300°C) and high pressures (50-100 atm),[6e, 7] the development of a practical catalytic system for the hydrogenation of CO2 into methanol still remains a challenge, as high activation energy barriers have to be overcome for the cleavage of the C=O bonds of CO2, albeit with favorable thermodynamics.[8] Heterogeneous catalysis for the hydrogenation of CO 2 into CH3OH has been extensively investigated, and Cu/Zn-based multi-component catalyst was found to be highly selective with a long life, but under relatively harsh reaction conditions (250 °C, 50 atm).[3b, 6d] Therefore, the production of methanol from CO2 by direct hydrogenation under mild conditions is still a great challenge for both academia and industry.
- Han, Zhaobin,Rong, Liangce,Wu, Jiang,Zhang, Lei,Wang, Zheng,Ding, Kuiling
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supporting information
p. 13041 - 13045
(2013/03/13)
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- Kinetics and mechanism of uncatalysed and ruthenium(III)-catalysed oxidation of D-panthenol by alkaline permanganate
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The oxidation of D-panthenol by MnO4-was studied in the absence and in the presence of ruthenium(III) catalyst in alkaline medium at 298 K and at constant ionic strength of 0.50 mol dm-3 by spectrophotometry. The stoi-chiometry in both the cases was [panthenol]: [MnO4-] = 1:4. The oxidation products were identified by IR and GC-MS. The reaction was first-order with respect to both MnO4- and ruthenium(III), while the orders with respect to both panthenol and alkali varied from first order to zero order as the concentrations increased. The effects of added products, ionic strength and dielectric constant were studied. The reaction constants, activation parameters and thermodynamic quantities were calculated for both the uncatalysed and catalysed reactions. Springer Science+Business Media B.V. 2009.
- Hosahalli, Rajeshwari V.,Savanur, Anita P.,Nandibewoor, Sharanappa T.,Chimatadar, Shivamurti A.
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experimental part
p. 237 - 246
(2011/10/18)
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- NOVEL COMPOUNDS AS CANNABINOID RECEPTOR LIGANDS
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Disclosed herein are cannabinoid receptor ligands of formula (I) wherein A1, A5, Rx, X4, and z are as defined in the specification. Compositions comprising such compounds, and methods for treating conditions and disorders using such compounds and compositions are also disclosed.
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Page/Page column 50; 51
(2010/04/23)
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- THIAZOLES AS CANNABINOID RECEPTOR LIGANDS
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Disclosed herein are cannabinoid receptor ligands of formula (I) wherein L1, A1, R1g, z, R2, R3, and R4 are as defined in the specification. Compositions comprising such compounds and methods for treating conditions and disorders using such compounds and compositions are also presented.
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Page/Page column 75-76
(2010/08/05)
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- METHOD FOR PRODUCING ALCOHOL BY HYDROGENATING LACTONE AND CARBOXYLIC ACID ESTER IN LIQUID PHASE
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Disclosed is a method for producing an alcohol from a lactone or a carboxylic acid ester, which enables to produce an alcohol from a lactone or a carboxylic acid ester under relatively mild conditions with high yield and high catalytic efficiency. This method also enables to produce an optically active alcohol from an optically active lactone or an optically active carboxylic acid ester. Specifically disclosed is a method for producing an alcohol by hydrogen reducing a lactone or a carboxylic acid ester in the presence of a catalyst containing ruthenium and a phosphine compound represented by the following general formula (1): wherein R1 represents a spacer; R2, R3, R4, R5, R6 and R7 independently represent a hydrogen atom, an alkyl group having 1-12 carbon atoms, an aryl group or a heterocyclic group; and R8, R9, R10, R11, R12 and R13 independently represent an alkyl group having 1-12 carbon atoms, an aryl group or a heterocyclic group.
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Page/Page column 13
(2010/01/29)
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- COMPOUNDS AS CANNABINOID RECEPTOR LIGANDS
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Disclosed herein are cannabinoid receptor ligands of formula (1) wherein Ring A and R1 are as defined in the specification. Compositions comprising such compounds, and methods for treating conditions and disorders using such compounds and compositions are also described
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Page/Page column 32
(2010/10/19)
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- Comparison of isoelectronic 8-HO-G and 8-NH2-G derivatives in redox processes
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8-Oxo-7,8-dihydroguanine (8-oxo-G) is the major lesion of oxidatively generated DNA damage. Despite two decades of intense study, several fundamental properties remain to be defined. Its isoelectronic 8-aminoguanine (8-NH 2-G) has also received considerable attention from a biological point of view, although its chemistry involving redox processes remains to be discovered. We investigated the one-electron oxidation and one-electron reduction reactions of 8-oxo-G and 8-NH2-G derivatives. The reactions of hydrated electrons (eaq-) and azide radicals (N 3?) with both derivatives were studied by pulse radiolysis techniques, and the transient absorption spectra were assigned to specific tautomers computationally by means of time-dependent DFT (TD-B3LYP/6-311G**//B1B95/6-31+G**) calculations. The protonated electron adducts of 8-NH2-G and 8-oxo-G showed a substantial difference in their absorption spectra, the unpaired electron being mainly delocalized in the imidazolyl ring and in the six-membered ring, respectively. On the other hand, the deprotonated forms of one-electron oxidation of 8-NH2-G and 8-oxo-G showed quite similar spectral characteristics. In a parallel study, the one-electron reduction of 8-azidoguanine (8-N3-G) afforded the same transient of one-electron oxidation of 8-NH2-G, which represents another example of generation of one-electron oxidized guanine derivatives under reducing conditions. Moreover, the fate of transient species was investigated by radiolytic methods coupled with product studies and allowed self- and cross-termination rate constants associated with these reactions to be estimated.
- Kaloudis, Panagiotis,D'Angelantonio, Mila,Guerra, Maurizio,Spadafora, Marie,Cismas, Crina,Gimisis, Thanasis,Mulazzani, Quinto G.,Chatgilialoglu, Chryssostomos
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experimental part
p. 15895 - 15902
(2010/01/29)
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- 5-SUBSTITUTED-2-PHENYLAMINO-BENZAMIDE AS MEK INHIBITOR
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An objective of the present invention is to provide compounds that exhibit strong MEK-inhibiting activity and are stable in vivo and soluble in water, which can be used as preventive or therapeutic agents for proliferative diseases. The compounds of the present invention and pharmaceutically acceptable salts thereof are represented by the following formula (1): [where R1, R2, R3, R4, and X are the same as defined in the present patent application].
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Page/Page column 122
(2008/06/13)
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- Effect of aliphatic spacer substitution on the reactivity of phenyl carbamate acrylate monomers
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Novel monoacrylate monomers with a carbamate secondary functionality and a terminal aryl group were synthesized to study the mechanisms that allow for increased reactivity of these monomers compared to typical monoacrylate monomers. To test for the possibility of hydrogen abstraction from the two-carbon aliphatic spacer group, varying methyl substituents were added to one or both of the spacer carbons. Single methylation at the α and β carbons showed no drastic effect on the polymerization rate. However, dual methylation of the a carbon reduced the overall polymerization rate by approximately 5-fold. Conversely, dual methylation at the β carbon reduced the polymerization rate by only 2-fold. Unsteady state analysis of the α,α-methylated monomer showed that the apparent kinetic constants approach that of traditional monoacrylate monomers. Thus, hydrogen abstraction appears to be a likely explanation for these unique substitution effects on monoacrylate reactivity where the substitution number and location have a profound impact on the polymerization rate of these novel monomers. Disubstitution at the α-position has the most profound influence on the rate.
- Beckel, Eric R.,Stansbury, Jeffrey W.,Bowman, Christopher N.
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p. 3093 - 3098
(2007/10/03)
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- 2,3,5-TRISUBSTITUTED PYRIDINES AS INHIBITORS OF CYCLOOXYGENASE-2
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The invention encompasses the novel compound of Formula (I) as well as a method of treating cyclooxygenase-2 mediated diseases comprising administration to a patient in need of such treatment of a non-toxic therapeutically effective amount of a compound of Formula (I). The invention also encompasses certain pharmaceutical compositions for treatment of cyclooxygenase-2 mediated diseases comprising compounds of Formula (I).
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- 2,3,5-trisubstituted pyridines as inhibitors of cyclooxygenase-2
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The invention encompasses the novel compound of Formula I as well as a method of treating cyclooxygenase-2 mediated diseases comprising administration to a patient in need of such treatment of a non-toxic therapeutically effective amount of a compound of Formula I. STR1 The invention also encompasses certain pharmaceutical compositions for treatment of cyclooxygenase-2 mediated diseases comprising compounds of Formula I.
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- 2-heterosubstituted-3-(4-methylsulfonyl)phenyl-5-trifluoromethyl pyridines as selective and orally active cyclooxygenase-2 inhibitors
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A series of novel 2-alkoxy, 2-thioalkoxy and 2-amino-3-(4- methylsulfonyl)phenylpyridines has been synthesized and shown to be highly potent and selective cyclooxygenase-2 (COX-2) inhibitors. Structure-activity relationship studies have demonstrated that central pyridine ring substituents play an important role in the COX-2 potency, selectivity vs the COX-1 enzyme, and oral activity.
- Dube, Daniel,Brideau, Christine,Deschenes, Denis,Fortin, Rejean,Friesen, Richard W.,Gordon, Robert,Girard, Yves,Riendeau, Denis,Savoie, Chantal,Chan, Chi-Chung
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p. 1715 - 1720
(2007/10/03)
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- Titanium-Catalyzed Diastereoselective Epoxidations of Ene Diols and Allylic Alcohols with β-Hydroperoxy Alcohols as Novel Oxygen Donors
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β-Hydroperoxy alcohols 1-4 serve as effective tridentate oxygen donors for the highly diastereo-selective, titanium-catalyzed epoxidation of ene diols 5a-e. Thus, in contrast to the bidentate tert-butyl hydroperoxide, the usual oxygen donor employed in Sharpless-type epoxidations and known to work poorly for polyhydroxy substrates, the tridentate β-hydroperoxy alcohols efficiently replace the tridentate epoxy diol products 6a-e in the titanium template and thereby the catalytic cycle is sustained by replenishing with efficacy the loaded complex necessary for the oxygen transfer. Irrespective of the substitution pattern of the double bond or the configuration (erythro versus threo) of the diol functionalities in the ene diol substrate, high diastereoselectivities are observed for the epoxy diol products. The high stereochemical control is due to the rigid transition state for the oxygen transfer, which is imposed by the multiple titanium-oxygen bonding and coordination in the titanium template. The observed erythro selectivity for the ene diol derives from the additional bonding of its homoallylic hydroxy group to the titanium center, which fixes the substrate conformation in such a way that the oxygen atom to be transferred approaches from the side of the allylic oxygen functionality (cf. loaded complex A). This additional binding of the bidentate ene diol in the titanium template is also manifested in the enhanced reactivity of the ene diol versus the monodentate allylic alcohols. Nevertheless, the less reactive allylic alcohols also display a high erythro selectivity, provided these monodentate substrates possess 1,2-allylic strain. For the first time a direct, diastereoselective, and catalytic epoxidation of ene diols has been made available for synthetic applications, without recourse to protection group methodology.
- Adam, Waldemar,Peters, Karl,Renz, Michael
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p. 3183 - 3189
(2007/10/03)
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- A Spectroscopic, Kinetic, and Product Study of the (CH3)2C(OH)CH2O2 Radical Self Reaction and Reaction with HO2
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A flash photolysis technique was used to measure the UV absorption spectrum of the peroxy radical (CH3)2C(OH)CH2O2 formed in the (CH3)3COH/Cl/O2 reaction system and to study the kinetics of its self reaction and reaction with the HO2 radical at room temperature and above: 2(CH3)2C(OH)CH2O2 -> 2(CH3)2C(OH)CH2O + O2 (5a); 2(CH3)2C(OH)CH2O2 -> (CH3)2C(OH)CH2OH + (CH3)2C(OH)CHO + O2 (5b); (CH3)2C(OH)CH2O2 + HO2 -> (CH3)2C(OH)CH2OOH + O2 (8).The spectrum of the radical resembles that of other β-hydroxyl substituted peroxy radicals in form and magnitude.Use of this and other known absorption cross sections in an appropriate chemical model of the system allowed k5, the branching ratio α (=k5a/k5), and k8 to be derived as a function of temperature (T = 306-398 K) by an iterative procedure involving the simulation of experimental decay traces recorded at several wavelengths: k5 = (1.4 +/- 0.6)E-14exp cm3 molecule-1 s-1; α = 0.59 +/- 0.15 (no discernible temperature dependence over this range); k8 = (5.6 +/- 2.0)E-14exp cm3 molecule-1 s-1.These expressions yield values for k5 and k8 of 4.8 and 14E-12 cm3 molecule-1 s-1 at 298 K, confirming the phenomena both of enhanced self reaction reactivity upon β-OH substitution and of a large rate coefficient for the reaction of all >/= C2 peroxy radicals with HO2.Product studies of reaction 5, using an FTIR-smog chamber system, confirmed the assumed reaction mechanism in 700 Torr of air at 296 K, namely the unique formation of the peroxy radical of interest, rapid decomposition of the alkoxy radical (formed in reaction 5a) through C-C bond scission, and subsequent reaction with O2 to yield formaldehyde and acetone (and HO2).A similar fate for the (CH3)2C(OH)CH2O radical is expected as part of the degradation of tert-butyl alcohol (TBA) and isobutene under tropospheric conditions.Furthermore, the product distribution results, when combined with the extrapolated k5 and k8 values, allow α be determined as 0.60 +/- 0.07 at 296 K, consistent with the value obtained from the flash photolysis study.As part of the smog chamber work, a relative rate technique was used to measure the rate coefficient for the reaction of Cl atoms with (CH3)2C(CH2Cl)OH as (9.2 +/- 1.1)E-12 cm3 molecule-1 s-1 at 296 K.
- Boyd, Andrew A.,Lesclaux, Robert,Jenkin, Michael E.,Wallington, Timothy J.
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p. 6594 - 6603
(2007/10/03)
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- Organotin-Mediated Monoacylation of Diols with Reversed Chemoselectivity: A Convenient Synthetic Method
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The organotin-mediated monoesterification of unsymmetrical diols with reversed chemoselectivity has been explored to ascertain scope and limits of the method and to provide an easy and convenient synthetic procedure.The reaction has been performed on a set of substituted diols with some acylating agents usually employed as protecting groups.Two different procedures have been devised to obtain either the desired diol monoesters directly or the corresponding trialkylsilyl ethers as protected derivatives.The latter provides a convenient approach to the preparation of easily interconvertible diol monoesters.Also, the reaction has been optimized as a one-pot procedure, avoiding the isolation and purification of the stannylated intermediates.The reversed monoesterification method has been successfully applied to 1,2-, 1,3-, and 1,4-diols of primary-secondary, primary-tertiary, and secondary-tertiary types and to ether functions containing 1,2-diols.Within its limits, the described method represents the first direct one-pot monoesterification of diols at the most substituted site, allowing some remarkable achievements as (a) an almost regiospecific reversed monobenzoylation of some 1,2-diols, (b) the selective acylation of the tertiary hydroxyl of a primary-tertiary diol, and (c) a highly selective preparation of secondary pivalate of primary-secondary diols.
- Reginato, Gianna,Ricci, Alfredo,Roelens, Stefano,Scapecchi, Serena
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p. 5132 - 5139
(2007/10/02)
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- Acid-Catalysed Hydration of Prop-2-en-1-ol and 2-Methylprop-2-en-1-ol: Correlation of Reactivity
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The kinetics of the acid-catalysed reaction of prop-2-en-1-ol and 2-methylprop-2-en-ol have been measured.The relative reactivity, solvent isotope (kH+/kD+) and change in acidity effects, and activation parameters, have been determined and found to be similar to those of other alkenes.While this correlation of results for the hydration of both these alkenols can be interpreted in terms of the conventional Ad-E2 mechanism, computed values for the lifetime of possible carbocation intermediates suggest that an alternative mechanism for the reaction of prop-2-en-1-ol, in which nucleophilic attack by the solvent is concerted with protonation, is feasible.
- Herlihy, Kevin P.
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p. 1345 - 1350
(2007/10/02)
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- A Mechanistic Characterization of the Spontaneous Ring Opening Process of Epoxides In Aqueous Solution: Kinetic and Product Studies
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A careful determination of the extent of rearrangement during epoxide hydration was carried out in conjunction with nuclear magnetic resonance kinetic studies for both propylene and isobutylene oxides.The complete pH-rate profile was mapped at ionic strength 2.0, and solvent kinetic isotope effects were determined for several limbs.Spectrophotometric analysis of the quantity of aldehyde formed by rearrangement in both the acidic and spontaneous limbs reveals that ionic strength has a profound effect.At ionic strength zero, more rearrangement product is generated in the acidic limb, whereas at ionic strength 2.0, larger amounts of aldehyde are formed in both regions.These results support the conclusion that a different carbocationic intermediate exists in the reaction mechanism for the acidic and spontaneous regions.The experimental observations of the spontaneous region can be explained by the existence of zwitterionic intermediate III.Observed solvent kinetic isotope effects, kH3O+/kD3O+, kHspon/kDspon, of 0.33+/-0.02, 1.78+/-0.25 and 0.35+/-0.03, 1.48+/-0.27 for propylene and isobutylene oxides, respectively, were dissected into components on the basis of classical product studies.At high ionic strength, isolation of compound I, an isobutyraldehyde isobutylene glycol acetal, supports the existence of intermediate III.Apparent partitioning ratios for both the β-hydroxy carbocation, II, and the zwitterion, III, are examined and contrasted.Detailed mechanistic proposals are advanced, and their congruence with a variety of observations described previously in this journal is outlined.
- Pocker, Y.,Ronald, B. P.,Anderson, K. W.
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p. 6492 - 6497
(2007/10/02)
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- One-electron Reduction of Halothane (2-Bromo-2-chloro-1,1,1-trifluoroethane) by Free Radicals. Radiation Chemical Model System for Reductive Metabolism
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The reaction mechanism of one-electron and radical-induced degradation of the general anaesthetic halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) has been investigated for γ-irradiated, oxygen-free aqueous solutions containing various alcohols or formate.Modern ion chromatography and conventional g.c.-m.s. methods were used as analytical tools for identification of end products.This includes quantitative determination of Cl- ions in the presence of Br- ions.Reduction of halothane by hydrated electrons, various alcohol radicals, and .CO2- proceeds via Br- elimination and CF3.CHCl radical formation as initial step. t-Butyl alcohol radicals .CH2C(CH3)2OH abstract bromine atoms to yield BrCH2C(CH3)2OH which suffers base-catalysed Br- elimination.Chain reactions leading to high Br- yields are observed in sulutions containing propan-2-ol, ethanol, methanol and formate.Based on 2k = 1E9 mol-1 dm3 s-1 for the dimerization of 2 CF3.CHCl radicals the following rate constants have been measured: k(CF3.CHCl + propan-2-ol) = 670 mol-1 dm3 s-1, k(CF3.CHCl + ethanol) = 130 mol-1 dm3 s-1, k(CF3.CHCl + metanol) = 27 mol-1 dm3 s-1 and k(CF3.CHCl + formate) = 2900 mol-1 dm3 s-1.Dimerization of CF3.CHCl leads to CF3CHClCHClCF3 which suffers base-catalysed HCl elimination to yield the two stereoisomers of CF3CH=CClCF3.The halothane results are compared with corresponding findings in CCl4-containing systems.
- Moenig, Joerg,Asmus, Klaus-Dieter
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p. 2057 - 2063
(2007/10/02)
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- Chemistry of (Glycidyloxy)propiolactones. An Intramolecular Transfer of Alkoxy Group in the Alcoholysis and Reduction Reactions
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An interesting intramolecular transfer of an acetal alkoxy group is observed in the alkaline alcoholysis and in reduction by LiAlH4 of α-methyl-α-((1-tert-butoxy-2-methyl-2,3-epoxypropyl)oxy)-β-propiolactone (3a).With either methanol or ethanol and NaOH at 30 deg C, the (glycidyloxy)propiolactone 3a cleaves to produce α-methylglycidaldehyde and either methyl or ethyl α-tert-butoxy-β-hydroxyisobutyrate.Reduction with LiAlH4 at 30 deg C also cleaves 3a, this time with partial reduction to give 2-methyl-2,3-epoxypropanol (6) and 2-methyl-2-tert-butoxypropane-1,3-diol (7).In each case the tert-butoxy group has been transferred to the α carbon of the β-lactone portion of 3a.
- Jedlinski, Zbigniew,Klimek-Slezak, Robert,Kowalczuk, Marek
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p. 2427 - 2429
(2007/10/02)
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- 2β-D-GLUCOPYRANOSYLOXY-2-METHYLPROPANOL IN ACACIA SIEBERANA VAR. WOODII
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A new diol glucoside, 2-β-D-glucopyranosyloxy-2-methylpropanol, the first reported naturally occurring monoglucoside of an aliphatic dihydric alcohol, was isolated from pods of Acacia sieberana var. woodii.Structure eucdation was based on 1H and 13C NMR spectroscopy, and anzymatic analyses.The compound was hydrolysed very slowly by almond β-glucosidase, but cleaved by a β-glucuronidase enzyme complex from Helix pomatia.Key Word Index - Acacia sieberana var. woodii; Mimosoideae; glycoside; novel diol glucoside; 2-methyl-1,2-propanediol aglycone; dihydric alcohol; glycol; diol lipids.
- Brimer, Leon,Christensen, S. Broegger,Nartey, Frederick
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p. 2005 - 2008
(2007/10/02)
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- Hydroboration. 57. Hydroboration with 9-Borabicyclononane of Alkenes Containing Representative Functional Groups
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The hydroboration of alkenes containing representative functional groups was examined with 9-borabicyclononane (9-BBN) in order to extend the hydroboration reaction for the preparation of functionally substituted organoboranes.Terminal alkenes containing a remote functional group are hydroborated with a remarkable regioselectivity (>=98percent terminal), producing the corresponding stable organoboranes. 9-BBN hydroborates the allylic derivatives so as to place boron essentially on the terminal carbon atom (>=97percent).The directive effect is further enhanced (>=99percent) in the case of β-methylallyl derivatives.The hydroboration of crotyl derivatives attaches boron predominantly at the 2-position, followed by an elimination-rehydroboration sequence.However, crotyl alcohol can be protected against elimination as the tert-butyl or tetrahydropyranyl ethers.The hydroboration-oxidation of ethyl crotonate involves a series of elimination, hydroboration, and condensation processes.In the vinyl, crotyl, and isobutenyl systems, the mesomeric effect of the substituent favors the placement of boron at the β-position, while the inductive effect favors the α-position, with the former effect predominating in most cases.Acyclic β-substituted organoboranes undergo rapid elimination.Nonpolar solvents and lower reaction temperatures decrease the rate of elimination.However, those derived from cyclic vinyl derivatives are relatively stable under neutral conditions, undergoing facile elimination in the presence of a base.
- Brown, Herbert C.,Chen, Jackson C.
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p. 3978 - 3988
(2007/10/02)
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- The Mechanism of Ozone-Alkene Reactions in the Gas Phase. A Mass Spectrometric Study of the Reactions of Eight Linear and Branched-Chain Alkenes
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The stable products of the low-pressure (4 - 8 torr (1 torr = 133.33 Pa)) gas-phase reactions of ozone with ethene, propene, 2-methylpropene, cis-2-butene, trans-2-butene, trans-2-pentene, 2,3-dimethyl-2-butene, and 2-ethyl-1-butene have been identified by using a photoionization mass spectrometer coupled to a stirred-flow reactor.The products observed are characteristic of (i) a primary Criegee split to an oxoalkane (aldehyde or ketone) and a Criegee intermediate, (ii) reactions of the Criegee intermediates such as unimolecular decomposition, secondary ozonide formation, etc., and (iii) secondary alkene chemistry involving OH and other free-radical products formed by the unimolecular decomposition of the Criegee intermediates.The secondary OH - alkene - O2 reactions account for a significant fraction of the alkene (CnH2n) consumed and lead to characteristic products such as Cn dioxoalkanes nH2n + 30)>, Cn acyloins nH2n + 32)>, and Cn alkanediols nH2n + 34)>.Cn oxoalkanes and Cn epoxyalkanes observed at m/e (CnH2n + 16) are probably formed primarily via epoxidation of the alkene by O3.A general mechanism has been proposed to account for the observations.
- Martinez, Richard I.,Herron, John T.,Huie, Robert E.
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p. 3807 - 3820
(2007/10/02)
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- Anti-bacterial compositions containing certain 3-nitropyrazoles
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Novel 1,4-disubstituted-3-nitropyrazoles having antimicrobial, parasiticidal, and herbicidal activity are prepared by a reaction sequence of which the individual steps are conventional. The new 3-nitropyrazoles are characterized by a 1-substituent and a usually carbonyl-containing 4-substituent. The novel 3(5)-nitro-4-pyrazole-carbonitrile is obtained as an intermediate in the preparation of the biologically-active compounds. Preferred compounds are 1-alkyl or -alkenyl-4-pyrazolecarboxamides and carbonitriles. The new compounds are particularly useful for the control of bacterial animal diseases.
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