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191.
Sodium dithionite initiated reactions of 1-bromo-1-chloro-2,2,2-trifluoroethane (1) with methyl and trimethylsilyl ethers of cyclopentanone and cyclohexanone enols (2a-d) in a MeCN/H2O system were investigated. 2-(2,2,2-Trifluoroethylidene)cyclopentanone (4a) and 2-(2,2,2-trifluoroethylidene)-cyclohexanone (4b), respectively, were obtained as the main products and isolated in reasonable yields. The reaction with a 1:1 mixture of 5- and 3-methyl substituted 1-methoxycyclohexenes, 2e and 2f, revealed strong influence of steric hindrance on the reaction rate; a mixture of 2-(2,2,2-trifluoroethylidene)-5-methylcyclohexanone (6) and 2-(2,2,2-trifluoroethylidene)-3-methylcyclohexanone (7) in a 9:1 ratio was formed. Ketones 4a and 4b were reduced to the corresponding alcohols 8 and 9 and the reaction of 4b with hydrazine gave an indazole derivative 10. 相似文献
192.
Beata Wodecka-Dus Malgorzata Adamczyk Jolanta Dzik Katarzyna Osinska 《The European Physical Journal B - Condensed Matter and Complex Systems》2016,89(2):52
The (BaxLa1?x)Ti1?x/4O3 (BLT,0.001 ≤ x ≤ 0.005) amorphous gel was prepared by sol-gel process. The electricalproperties of obtained materials has been investigated by impedance spectroscopy. Detailedanalysis of impedance spectra allowed to propose an adequate equivalent circuit, whichdescribed the electric properties of discussed materials very well. Basing on the obtainedcircuits and the fitting procedure the grain and grain boundary resistivity was determinedas a function of temperature and La concentration. With increase of La admixture thecontribution of grain and grains impedance to the bulk impedance changes. It was foundthat the small amount of La additive decreases the blocking factor of the grain boundaryin the temperature range 600–850 K, whereas the amount of La on the level of 0.4–0.5 mol.%causes the sharp increase of the mentioned factor. The fact may be attributed to adecrease of grain activation energy and increase of the grain boundary one. 相似文献
193.
Anna Bahyrycz Krzysztof Ciepliński Jolanta Olko 《Journal of Fixed Point Theory and Applications》2016,18(2):433-444
In this paper we prove, using the fixed point method, the generalized Hyers–Ulam stability of two functional equations in complete non-Archimedean normed spaces. One of these equations characterizes multi-Cauchy–Jensen mappings, and the other gives a characterization of multi-additive-quadratic mappings. 相似文献
194.
Piotr Kowalski Jolanta Jaśkowska Andrzej J. Bojarski Beata Duszyńska 《Journal of heterocyclic chemistry》2008,45(1):209-214
195.
Acyl phosphate monoesters are readily prepared biomimetically activated anionic derivatives of carboxylic acids that react rapidly with amines in water to form amides. A plot of the logarithms of the rate constants for the reactions of a series of primary amines with benzoyl methyl phosphate depends on the pKa of the conjugate acids of the amines (beta(nuc) approximately 0.9). This provides a simple and quantitative basis for regioselective acylation with these reagents. 相似文献
196.
Xiaoyi Gong Margaret Figus Jolanta Plewa Dorothy A. Levorse Lili Zhou Christopher J. Welch 《Chromatographia》2008,68(3-4):219-225
The acid dissociation constant (pK a) is a key physicochemical parameter for characterizing active pharmaceutical ingredients (APIs). Early determination of pK a values is highly desirable in drug discovery, pharmaceutical process research and formulation design. To overcome the challenges of limited sample availability and potential low purity of API samples at early stages of drug development, as well as to increase sample analysis throughput, a multiplexed 96-channel capillary electrophoresis with UV detection was evaluated as a practical approach for high throughput pK a estimation of proprietary APIs in support of pharmaceutical research. Proprietary APIs with diverse structures were examined using the approach. The pK a values were successfully determined with good accuracy and precision. System robustness was demonstrated and analysis of at least eight samples can be completed within 1 h. A rapid pK a estimation procedure for marginally soluble APIs was proposed by performing single-point multiplexed CE–UV measurement without extrapolation using 10 or 20% methanol as co-solvent. Direct pK a estimation of APIs using DMSO solution samples and crude reaction samples containing a large amount of solvents and reagents and high level of impurities was also demonstrated using the multiplexed CE–UV approach. 相似文献
197.
Kong Y Grembecka J Edler MC Hamel E Mooberry SL Sabat M Rieger J Brown ML 《Chemistry & biology》2005,12(9):1007-1014
Targeting the microtubule system represents an attractive strategy for the development of anticancer agents. In this study, we report a class of combretastatin A-4 (CA-4) analogs derivatized with a boronic acid moiety replacing the hydroxyl group on the C-ring of CA-4. Docking studies of the X-ray structures of our aryl-boronic analogs onto an X-ray structure of the alpha,beta-tubulin heterodimer suggested that cis-6 was a potent inhibitor of the colchicine binding. The model indicated that there would be strong hydrogen bonding between the boronic acid moiety and Thr-179 and Val-181 of alpha-tubulin. We demonstrate that the cis-6 boronic acid bioisostere of CA-4: (1) inhibits tubulin assembly, (2) competitively displaces colchicine, and (3) is a low-nanomolar inhibitor of human cancer cell lines. We present this isostere as a class of potent analogs of CA-4. 相似文献
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