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Evidence is presented demonstrating the existence of two paths to the title processes which arise from a common intermediate. A rationale involving catalyzed addition of the diazo compound to the olefin and carbenoid addition to the olefin is proposed. The penultimate intermediate has one new CC bond formed. It is partitioned between products by forming the second CC bond or formation of a hydrocarbenoid allyl complex which collapses to the allylic CH insertion products. Cyclopropanation occurs stereospecifically. The proposed mechanism accounts for the stereospecificity of cyclopropanation, the variance of syn/anti ratios with catalyst concentration when diazoacetic ester is employed and optical inductions with chiral catalysts. The question of whether the alleged carbenoid and/or the penultimate intermediate contain N2 is not answered although it is felt that a cupro-cyclobutane intermediate is the most probable intermediate before product partitioning. 相似文献
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Amino acids in foods exist in a free form or bound in peptides, proteins, or nonpeptide bonded polymers. Naturally occurring L-amino acids are required for protein synthesis and are precursors for essential molecules, such as co-enzymes and nucleic acids. Nonprotein amino acids may also occur in animal tissues as metabolic intermediates or have other important functions. The development of bacterially derived food proteins, genetically modified foods, and new methods of food processing; the production of amino acids for food fortification; and the introduction of new plant food sources have meant that protein amino acids and amino acid enantiomers in foods can have both nutritional and safety implications for humans. There is, therefore, a need for the rapid and accurate determination of amino acids in foods. Determination of the total amino acid content of foods requires protein hydrolysis by various means that must take into account variations in stability of individual amino acids and resistance of different peptide bonds to the hydrolysis procedures. Modern methods for separation and quantitation of free amino acids either before or after protein hydrolysis include ion exchange chromatography, high performance liquid chromatography (LC), gas chromatography, and capillary electrophoresis. Chemical derivatization of amino acids may be required to change them into forms amenable to separation by the various chromatographic methods or to create derivatives with properties, such as fluorescence, that improve their detection. Official methods for hydrolysis and analysis of amino acids in foods for nutritional purposes have been established. LC is currently the most widely used analytical technique, although there is a need for collaborative testing of methods available. Newer developments in chromatographic methodology and detector technology have reduced sample and reagent requirements and improved identification, resolution, and sensitivity of amino acid analyses of food samples. 相似文献
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Ko-Hsiu Lu Heng-Hsiung Wu Renn-Chia Lin Ya-Chiu Lin Peace Wun-Ang Lu Shun-Fa Yang Jia-Sin Yang 《Molecules (Basel, Switzerland)》2021,26(1)
Osteosarcoma, the most prevalent malignant bone tumor in the pediatric age group, is responsible for the great majority of cancer-associated deaths owing to its highly metastatic potential. The anti-metastatic effects of the new curcumin analogue L48H37 in human osteosarcoma are still unknown; hence, we investigated whether L48H37 represses human osteosarcoma cells’ biological behavior of migratory potential and invasive activities and attempted to delve into its underlying mechanisms. L48H37 up to 5 μM inhibited, without cytotoxicity, the motility, migration, and invasion of human osteosarcoma U2OS and MG-63 cells. In U2OS cells, the human protease array revealed an obvious decrease in urokinase plasminogen activator (uPA) expression after L48H37 treatment, and L48H37 actually reduced the level, protein and mRNA expression, and promoter activity of uPA dose-dependently. L48H37 decreased the phosphorylation of STAT3, JAK1, JAK2, and JAK3 in U2OS cells, but did not affect the phosphorylation of ERK, JNK, p38, and Akt. Using colivelin, an activator of STAT3, the L48H37-induced decrease in uPA and migratory potential could be countered as expected. Collectively, L48H37 represses the invasion and migration capabilities of U2OS and MG-63 cells by the suppression of uPA expression and the inhibition of JAK/STAT signaling. These results suggest that L48H37 may be a potential candidate for anti-metastatic treatment of human osteosarcoma. 相似文献
4.
Luke Green Keith Livingstone Dr. Sophie Bertrand Dr. Simon Peace Dr. Craig Jamieson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(65):14866-14870
A range of 1,3,4-oxadiazoles have been synthesized using a UV-B activated flow approach starting from carboxylic acids and 5-substituted tetrazoles. The application of UV light represents an attractive alternative to the traditional thermolytic approach and has demonstrated comparable efficiency and versatility, with a diverse substrate scope, including the incorporation of highly substituted amino acids. 相似文献
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Malose J. Mphahlele Mutshinyalo S. Nwamadi Peace Mabeta 《Journal of heterocyclic chemistry》2006,43(2):255-260
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B. Suryanarayanan B. W. Peace K. G. Mayhan 《Journal of polymer science. Part A, Polymer chemistry》1974,12(5):1089-1107
In the first of a two-part series, a study has been made of the anionic polymerization of a five-membered cyclocarbosiloxane, 2,2,5,5-tetramethyl-1-oxa-2,5-disilacyclopentane. The polymerization was initiated by lithium n-butyldiphenylsilanolate in the presence of tetrahydrofuran. The chemical shifts of the protons of the cyclic monomer and the polymer were found to be different, and therefore the rate of polymerization was obtained in an NMR spectrometer. The effects of varying the concentrations of THF, initiator, and water upon the rate of polymerization and upon the molecular weight and the molecular weight distribution were investigated. At a constant concentration of monomer and initiator, the rate of polymerization increased when the THF concentration was increased. At a constant concentration of monomer and THF the rate of polymerization reached a constant value when the initiator concentration was varied. The molecular weight and the molecular weight distribution were dependent upon the initiator to water ratio, whereas water concentration had little effect on the rate of polymerization. Essentially monodispersed polymers were obtained when the concentration of initiator was in large excess to that of water or vice versa. A bimodal distribution in molecular weight was obtained when the concentration of initiator was approximately equal to that of water. The apparent activation energy of polymerization was 12.7 kcal/mole. 相似文献
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David S. Wulfman Bradford G. McGibboney Earl K. Steffen Nguyen V. Thinh Robert S. McDaniel Billy W. Peace 《Tetrahedron》1976,32(11):1257-1265
Experimental and structural details are presented for the addition of bis-methoxycarbonyl carbene to a number of olefins employing homogeneous and heterogeneous catalyzed decompositions of dimethyl diazomalonate by copper and silver salts. The cyclopropanations are stereospecific and are accompanied by appreciable amounts of allylic C-H insertion products which could formally be derived from allylic radical or ionic intermediates. Cyclopropanation with cis 2-heptene proceeds 5.20 times as fast as with the trans isomer and cyclohexene reacts 4.90 times faster than 1-methyl cyclohexene when the catalyst is iodo(trimethyl phosphite)copper(I). 相似文献
10.
B. Suryanarayanan B. W. Peace K. G. Mayhan 《Journal of polymer science. Part A, Polymer chemistry》1974,12(5):1109-1123
A study was conducted of the anionic polymerization of a series of methyl- and/or phenyl-substituted five-membered cyclocarbosiloxanes. The polymerization was initiated by lithium n-butyldiphenylsilanolate in the presence of tetrahydrofuran. The rate of conversion of monomer to polymer was measured in an NMR spectrometer. The rate of polymerization was largely dependent upon the structure of the growing chain ends. The apparent activation energies were in the range 10–14 kcal/mole for the series. 相似文献