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991.
Shu-Ren Rao Seiichi Inokuma Jun Nishimura 《Journal of inclusion phenomena and macrocyclic chemistry》1995,23(4):329-341
A variety of new three-bridged cyclophanes, clefts4–14, have been conveniently prepared, and their cation-binding properties have been examined. Compounds4–6 have a special affinity for alkali metal cations. Ethyl ester5 and methyl ester4 selectively formed 2:1 complexes with K+ and Na+ ions, respectively. Clefts11–13, which possess pyridyl groups, bind Ag+ cation exclusively.1H NMR titration studies confirmed that11 or12, having 2- or 3-pyridyl groups, form a 1:1 complex with Ag+ cation, while13, with 4-pyridyl ligating groups, forms a 2:1 complex. Cleft10, with aminimide groups, also shows an affinity for Ag+ cation in a 2:1 ratio in a polar solvent, while it forms a 1:1 complex in a nonpolar solvent. The same solvent effect was observed for clefts13 and15c, which is discussed qualitatively. 相似文献
992.
Sascha Brass 《Tetrahedron》2006,62(8):1777-1786
A highly efficient synthesis based on inexpensive and readily available starting material towards the pharmacologically interesting class of substituted 2,3,4,7-tetrahydro-1H-azepines via a ring-closing metathesis (RCM) approach employing Grubbs catalysts 1 and 2 is described. The influence of the substituents R1 and R2 on the outcome of the RCM reaction is discussed. The seemingly first example of an RCM approach towards seven-membered azacycles bearing a substituent at the alkene moiety utilizing Grubbs catalyst 1 is presented. 相似文献
993.
MANSOORI Yagoub TATAROGLU SEYIDOV Firdovsi BOHLOOLI Shahrbanoo ZAMANLOO Mohammad Reza IMANZADEH Gholam Hassan 《中国化学》2007,25(12):1878-1882
Esterification or transesterification reactions are usually carried out in the presence of homogeneous or heterogeneous catalysts. However, recently a new method was reported for the esterification of carboxylic acids by tributyl borate under solvent- and catalyst-free conditions. In order to show the synthetic ability of trialkyl borate esters in the esterification reactions, here, the esterification of other carboxylic acids and diacids by tributyl-, triisoamyl-, and tribenzyl borate under the same conditions were reported. Some of the prepared ester and diester products have found wide applications as plasticizers and synthetic ester base lubricants. The esterification reactions have been cleanly carried out in the absence of any solvent under catalyst-free conditions. The maximum rate belongs to isoamyl trichloroacetate (VIb) which reached about 76% within about 6.5 h. On the basis of obtained findings, it seems that electron withdrawing groups on carboxylic acid facilitate the esterification reaction. 相似文献
994.
This paper describes the synthesis and characterization of a series of TRITON™ X-based surfactants with a predominantly alkyl phenol ethoxylate (APE) backbone and a phosphate ester chain end. Four phosphate-terminated TRITON™ X (or APE) derivatives (OPE2-OPO(OH)2, OPE5-OPO(OH)2, OPE10-OPO(OH)2, and NPE10-OPO(OH)2) were prepared from commercially available octyl phenol ethoxylate (OPE) of different oxyethylene units (n = 2, 5 and 10), nonyl phenol ethoxylate (NPE) of 10 oxyethylene units and phosphorous pentoxide via a simple condensation reaction. Depending on their composition and chain length of oxyethylene units used in the reaction, the surfactants show different self-charring behaviors. The phosphate-terminated TRITON™ X of the lowest number of oxyethylene units (i.e. OPE2-OPO(OH)2) gives the largest amount of char (up to 23 wt%) at 600 °C under air condition. The carboxylic acid-terminated TRITON™ X derivatives (i.e. OPE-COOH) were also tested for comparison. 相似文献
995.
Ana P Esteves Danielle M Goken Lee J Klein Maria J Medeiros Dennis G Peters 《Journal of Electroanalytical Chemistry》2003,560(2):F167
Cyclic voltammograms for the reduction of ethyl 2-bromo-3-(3′,4′-dimethoxyphenyl)-3-(propargyloxy)propanoate (1) at glassy carbon electrodes in dimethylformamide containing tetraalkylammonium salts exhibit three prominent waves corresponding to cleavage of the carbon–bromine bond and to subsequent reduction of ethyl trans-3-(3′,4′-dimethoxyphenyl)-prop-2-enoate (4). Controlled-potential electrolyses of 1 at potentials corresponding to reduction of the carbon–bromine bond afford 4 as the major product with an average yield of 56%. In the presence of a proton donor (1,1,1,3,3,3-hexafluoro-2-propanol), the quantity of 4 decreases slightly, and 2-(3′,4′-dimethoxyphenyl)-3-(ethoxycarbonyl)-4-methyl-2,5-dihydrofuran (3) is obtained in moderate amount (26%). We propose a mechanistic scheme whereby the major products are formed via a combination of one- and two-electron processes. 相似文献
996.
Sonya Y. Zareva 《Central European Journal of Chemistry》2006,4(4):695-707
2-[(2-Ethoxy-3,4-dioxocyclobut-1-en-yl)amino]propanamide (N-alaninamidoamide of squaric acid ethyl ester) has been characterized
structurally and spectroscopically by ab initio calculations and IR-LD spectroscopy of oriented crystals suspended in a nematic liquid crystal. The results are compared
with single crystal X-ray structures illustrating the possibilities of this experimental approach to obtaining structural
information as well as assigning IR bands. 相似文献
997.
5-(7-Hydroxyhept-3-enyl)-1,2-dithiolan-3-one 1-oxide 1 possessing both the 1,2-dithiolan-3-one 1-oxide five-membered ring and the double bond at the gamma position of the heterocycle, characteristic of the antibiotic leinamycin, was synthesized. In addition, the activated ester form of 1 was prepared that may be useful for coupling 1 to certain DNA-binding agents. 相似文献
998.
Chong LT Bandyopadhyay P Scanlan TS Kuntz ID Kollman PA 《Journal of computational chemistry》2003,24(12):1371-1377
Direct hydroxide attack on the scissile carbonyl of the substrate has been suggested as a likely mechanism for esterase antibodies elicited by phosphonate haptens, which mimic the transition states for the alkaline hydrolysis of esters.1 The unique amidase activity of esterase antibody 43C9 has been attributed to nucleophilic attack by an active-site histidine residue.2 Yet, the active site of 43C9 is strikingly similar to those of other esterase antibodies, particularly 17E8. We have carried out quantum mechanical calculations, molecular dynamics simulations, and free energy calculations to assess the mechanism involving direct hydroxide attack for 43C9. Results support this mechanism and suggest that the mechanism is plausible for other antiphosphonate antibodies that catalyze the hydrolysis of (p-nitro)phenyl esters. 相似文献
999.
Tumor promoters such as phorbol esters bind strongly to protein kinase C (PKC) isozymes to induce their activation. Since each PKC isozyme is involved in diverse biological events in addition to tumor promotion, the isozymes serve as promising therapeutic targets. Tumor promoters bind to the C1A and/or C1B domain of conventional (alpha, betaI, betaII, and gamma) and novel PKC isozymes (delta, epsilon, eta, and theta). As these C1 domains play differential roles in PKC activation and their translocation in cells, the development of agents with binding selectivity for individual C1 domains is a pressing need. For this purpose, we established a synthetic C1 peptide library of all PKC isozymes. The library enabled us to identify indolactam-V (1) as a promising lead compound. Our diverse structure-activity studies on 1 indicated that the position of the hydrophobic substituent on the indole ring dominates the PKC isozyme- and C1 domain-selective binding rather than conformation of the nine-membered lactam. Moreover, we suggested that the indole ring of 1 could be involved in the CH/pi interaction with Pro-11 of the C1B domain of PKCdelta. This invaluable information will lead to the structural optimization of the PKCdelta ligand as exemplified by the design and synthesis of naphtholactam-V8 (21). 相似文献
1000.
Characterization of fatty acid methyl esters by thermal analysis 总被引:1,自引:0,他引:1
F. J. Rey O. Chamorro F. J. Martín Gil J. Martín Gil 《Journal of Thermal Analysis and Calorimetry》1993,40(2):463-473
The thermal stability of selected straight-chain (C6-C14) esters of fatty acids has been studied by TG-DTG and DTA analysis. In DTG, a peak is detected between 84° and 125° C followed by a main effect in the range 105°–215°C, whereas in DTA only an exothermic peak appears in the range of 126.5° to 187°C (onset temperatures). The temperatures of these effects have been related with ignition points, molecular weights and boiling points. The characteristics of melting and recrystallization of the above fatty acid methyl esters and those with carbon numbers between C14 and C24 have been established by DSC along the melting range between ?83° and 50°C. Polymorphism appears in caproic, heptanoic, palmitic and stearic acid methyl esters. 相似文献