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541.
542.
Zehua Wang Yasheng Zhu Xiaoguang Pan Gang Wang Lei Liu 《Angewandte Chemie (International ed. in English)》2020,59(8):3053-3057
A direct and enantioselective oxidative cross‐coupling of racemic 2,2‐diarylacetonitriles with electron‐rich (hetero)arenes has been described, which allows for efficient construction of triarylmethanes bearing all‐carbon quaternary stereocenters with excellent chemo‐ and enantioselectivity. The reaction has an excellent functional group tolerance, and exhibits a broad scope with respect to both 2,2‐diarylacetonitrile and (hetero)arene components. The rich chemistry of the cyano group allows for facile synthesis of other valuable chiral triarylmethanes bearing all‐carbon quaternary centers that are otherwise difficult to access. 相似文献
543.
Zongwei Yue Hiu C. Lam Kaiqi Chen Ittipon Siridechakorn Yaxi Liu Khanitha Pudhom Xiaoguang Lei 《Angewandte Chemie (International ed. in English)》2020,59(10):4115-4120
The rhytidenone family comprises spirobisnaphthalene natural products isolated from the mangrove endophytic fungus Rhytidhysteron rufulum AS21B. The biomimetic synthesis of rhytidenone A was achieved by a Michael reaction/aldol/lactonization cascade in a single step from the proposed biosynthetic precursor rhytidenone F. Moreover, the mode of action of the highly cytotoxic rhytidenone F was investigated. The pulldown assay coupled with mass spectrometry analysis revealed the target protein PA28γ is covalently attached to rhytidenone F at the Cys92 residue. The interactions of rhytidenone F with PA28γ lead to the accumulation of p53, which is an essential tumor suppressor in humans. Consequently, the Fas‐dependent signaling pathway is activated to initiate cellular apoptosis. These studies have identified the first small‐molecule inhibitor targeting PA28γ, suggesting rhytidenone F may serve as a promising natural product lead for future anticancer drug development. 相似文献
544.
Zongwei Yue Dr. Hiu C. Lam Kaiqi Chen Dr. Ittipon Siridechakorn Yaxi Liu Prof. Dr. Khanitha Pudhom Prof. Dr. Xiaoguang Lei 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(10):4144-4149
The rhytidenone family comprises spirobisnaphthalene natural products isolated from the mangrove endophytic fungus Rhytidhysteron rufulum AS21B. The biomimetic synthesis of rhytidenone A was achieved by a Michael reaction/aldol/lactonization cascade in a single step from the proposed biosynthetic precursor rhytidenone F. Moreover, the mode of action of the highly cytotoxic rhytidenone F was investigated. The pulldown assay coupled with mass spectrometry analysis revealed the target protein PA28γ is covalently attached to rhytidenone F at the Cys92 residue. The interactions of rhytidenone F with PA28γ lead to the accumulation of p53, which is an essential tumor suppressor in humans. Consequently, the Fas-dependent signaling pathway is activated to initiate cellular apoptosis. These studies have identified the first small-molecule inhibitor targeting PA28γ, suggesting rhytidenone F may serve as a promising natural product lead for future anticancer drug development. 相似文献
545.
Preparative separation of vitexin and isovitexin from pigeonpea extracts with macroporous resins 总被引:1,自引:0,他引:1
Vitexin and isovitexin are a pair of isomeric compounds known as the major constituents in pigeonpea leaves and possess various pharmacological activities. In the present study, the preparative separation of vitexin and isovitexin with macroporous resins (Nankai Hecheng S & T, Tianjin, China) was studied. The performance and adsorption characteristics of eight macroporous resins including ADS-5, ADS-7, ADS-8, ADS-11, ADS-17, ADS-21, ADS-31 and ADS-F8 have been evaluated. The research results indicate that ADS-5 resin is most appropriate for the separation of vitexin and isovitexin. Langmuir and Freundlich isotherms were used to describe the interactions between solutes and resin at different temperatures, and the equilibrium experimental data were well fitted to the two isotherms. Column packed with ADS-5 resin was used to perform dynamic adsorption and desorption tests to optimize the separation process. The optimum parameters for adsorption were as follows: the concentration of vitexin and isovitexin in sample solution: 0.22 and 0.40mg/mL, respectively, processing volume: 3 BV, flow rate: 1mL/min, pH 4, temperature: 25 degrees C; for desorption: ethanol-water (40:60, v/v), 5 BV as an eluent, flow rate: 1mL/min. After one run treatment with ADS-5 resin, the contents of vitexin and isovitexin were increased 4.07-fold and 11.52-fold from 0.86%, 1.53% to 3.50% and 17.63%, the recovery yields were 65.03% and 73.99%, respectively. In conclusion, the preparative separation of vitexin and isovitexin can be easily and effectively achieved via adsorption and desorption on ADS-5 resin, and the method can be referenced for the separation of other flavone C-glucosides from herbal materials. 相似文献
546.
Hypothiocyanite (OSCN-) hydrolyzes under alkaline conditions to give thiocarbamate-S-oxide (H2NC(=O)SO-, the conjugate base of carbamothioperoxoic acid) via a mechanism that involves rate-limiting nucleophilic attack of OH- on OSCN-, followed by fast protonation (with no net consumption of H+/OH- at pH 11.7). Thiocarbamate-S-oxide has been characterized by 13C NMR, 15N NMR, UV spectroscopy, and ion chromatography. It has also been independently synthesized by the reaction of thiocarbamate (H2NC(=O)S-) and hypochlorite (OCl-). The properties of thiocarbamate-S-oxide that is produced by hydrolysis of OSCN- and by oxidation of H2NC(=O)S- are the same. The possible relevance of thiocarbamate-S-oxide in human peroxidase defense mechanisms remains to be explored. 相似文献
547.
548.
Xiaoguang Zhang Xuan Weng Feng Tian Wenbo Zhang Lixia Xi Guangyong Zhang 《Optics Communications》2011,284(18):4156-4160
This paper reports the DSP-based prototype compensator we have made to compensate the polarization mode dispersion (PMD) in fibers. It was tested in one channel of a 40 × 43-Gb/s DWDM DQPSK system, which is the commercial product line, either in the back-to-back case by using a PMD emulator, or in a 1200-km transmission testbed. The prototype showed a good performance under the tests of fast SOP and PSP rotation, DGD jump variation, and moderate knock on the testbed in a period as long as 12 h. 相似文献
549.
550.
Wang X Conway W Fernandes D Lawrance G Burns R Puxty G Maeder M 《The journal of physical chemistry. A》2011,115(24):6405-6412
The kinetics of the interactions of aqueous ammonia with aqueous carbon dioxide/carbonate species has been investigated using stopped-flow techniques by monitoring the pH changes via indicators. The reactions include the reversible formation of ammonium carbamate/carbamic acid. A complete reaction mechanism has been established, and the temperature dependence of all rate and equilibrium constants including the protonation constant of the amine between 15 and 45 °C are reported and analyzed in terms of Arrhenius, Eyring, and van't Hoff relationships. 相似文献