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821.
Bergueiro J Montenegro J Cambeiro F Saá C López S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(14):4401-4410
This paper presents a full account of the use of Hiyama cross-coupling reactions in a highly convergent approach to retinoids in which the key step is construction of the central C10-C11 bond. Representatives of two families of oxygen-activated dienyl silanes (ethoxysilanes and silanols) and of all reported families of "safety-catch" silanols (siletanes, silyl hydrides, allyl-, benzyl-, aryl-, 2-pyridyl- and 2-thienylsilanes) were regio- and stereoselectively prepared and stereospecifically coupled to an appropriate electrophile by treatment with a palladium catalyst and a nucleophilic activator. Both all-trans and 11-cis-retinoids, and their chain-demethylated analogues, were obtained in good yields regardless of the geometry (E/Z) and of the steric congestion in each fragment. This comprehensive study conclusively establishes the Hiyama cross-coupling reaction, with its mild reaction conditions and stable, easily prepared, ecologically advantageous silicon-based coupling partners, as the most effective route to retinoids reported to date. 相似文献
822.
Laszlo P. Csernai Astrid Sk?lvik D. J. Wang Daniel Strottman Csaba Anderlik Yun Cheng Yu L. Yan Ben H. Sa 《Central European Journal of Physics》2012,10(6):1271-1273
Collective flow is studied in a 3+1D fluid dynamical model with globally symmetric, peripheral initial conditions, taking into account the shear flow. At $\sqrt {s_{NN} } $ = 2.76 TeV in semi-peripheral Pb+Pb collisions this leads to rotation, while at more peripheral collisions with high resolution and low numerical viscosity, the initial development of a Kelvin-Helmholz instability is observed. This effect provides a precision tool for studying the viscosity of Quark-Gluon Plasma. 相似文献
823.
Nicolas Creusot Saïd Kinani Patrick Balaguer Nathalie Tapie Karyn LeMenach Emmanuelle Maillot-Maréchal Jean-Marc Porcher Hélène Budzinski Sélim Aït-Aïssa 《Analytical and bioanalytical chemistry》2010,396(2):569-583
Many environmental endocrine-disrupting compounds act as ligands for nuclear receptors. Among these receptors, the human pregnane
X receptor (hPXR) is well described as a xenobiotic sensor to various classes of chemicals, including pharmaceuticals, pesticides,
and steroids. To assess the potential use of PXR as a sensor for aquatic emerging pollutants, we employed an in vitro reporter
gene assay (HG5LN-hPXR cells) to screen a panel of environmental chemicals and to assess PXR-active chemicals in (waste) water
samples. Of the 57 compounds tested, 37 were active in the bioassay and 10 were identified as new PXR agonists: triazin pesticides
(promethryn, terbuthryn, terbutylazine), pharmaceuticals (fenofibrate, bezafibrate, clonazepam, medazepam) and non co-planar
polychlorobiphenyls (PCBs; PCB101, 138, 180). Furthermore, we detected potent PXR activity in two types of water samples:
passive polar organic compounds integrative sampler (POCIS) extracts from a river moderately impacted by agricultural and
urban inputs and three effluents from sewage treatment works (STW). Fractionation of POCIS samples showed the highest PXR
activity in the less polar fraction, while in the effluents, PXR activity was mainly associated with the dissolved water phase.
Chemical analyses quantified several PXR-active substances (i.e., alkylphenols, hormones, pharmaceuticals, pesticides, PCBs,
bisphenol A) in POCIS fractions and effluent extracts. However, mass-balance calculations showed that the analyzed compounds
explained only 0.03% and 1.4% of biological activity measured in POCIS and STW samples, respectively. In effluents, bisphenol
A and 4-tert-octylphenol were identified as main contributors of instrumentally derived PXR activities. Finally, the PXR bioassay provided
complementary information as compared to estrogenic, androgenic, and dioxin-like activity measured in these samples. This
study shows the usefulness of HG5LN-hPXR cells to detect PXR-active compounds in water samples, and further investigation
will be necessary to identify the detected active compounds. 相似文献
824.
Saúl A. Blanco 《Journal of Algebraic Combinatorics》2013,38(3):585-596
We define the shortest path poset SP(u,v) of a Bruhat interval [u,v], by considering the shortest u–v paths in the Bruhat graph of a Coxeter group W, where u,v∈W. We consider the case of SP(u,v) having a unique rising chain under a reflection order and show that in this case SP(u,v) is a Gorenstein? poset. This allows us to derive the nonnegativity of certain coefficients of the complete cd-index. We furthermore show that the shortest path poset of an irreducible, finite Coxeter group exhibits a symmetric chain decomposition. 相似文献
825.
We extend the applicability of Newton’s method for approximating a solution of a nonlinear operator equation in a Banach space setting using nondiscrete mathematical induction concept introduced by Potra and Ptak. We obtain new sufficient convergence conditions for Newton’s method using Lipschitz and center-Lipschitz conditions instead of only the Lipschitz condition used in F.A.Potra, V.Ptak, Sharp error bounds for Newton’s process, Numer. Math., 34 (1980), 63–72, and F.A.Potra, V.Ptak, Nondiscrete Induction and Iterative Processes, Research Notes in Mathematics, 103. Pitman Advanced Publishing Program, Boston, 1984. Under the same computational cost as before, we provide: weaker sufficient convergence conditions; tighter error estimates on the distances involved and more precise information on the location of the solution. Numerical examples are also provided in this study. 相似文献
826.
Miodrag K. Radović Čedomir A. Maluckov Jugoslav P. Karamarković Saša A. Rančev Slobodan D. Mitić 《Brazilian Journal of Physics》2013,43(3):145-151
The electrical breakdown of a gas subject to an up-ramping external voltage is studied, experimentally and theoretically, under conditions leading to the appearance of a positive corona at the anode in the pre-breakdown regime. Experimentally, voltage ramps with various rates k in the interval ranging from 0.3 V/s to 26 kV/s are applied to the diode, with the histogram of breakdown voltages being recorded for each rate. The theoretical model gives attention to the pre-breakdown multiplication causing the corona, which tends to reduce the statistical time delay $t_{S}$ before the primary electron is released and hence to make $t_{S}$ comparable to the formative time $t_{F}$ . The multiplication being therefore expected to affect the voltage dependence of the electron yield, a nonlinear equation relating the yield to the overvoltage is introduced. The resulting theoretical expression for the breakdown voltage distribution agrees well with the experimental histograms. Especially noteworthy is the good agreement with the low-voltage tail of the distribution, a segment of the data that has challenged previous theoretical analyses of the problem. 相似文献
827.
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830.
Ohkanda J Strickland CL Blaskovich MA Carrico D Lockman JW Vogt A Bucher CJ Sun J Qian Y Knowles D Pusateri EE Sebti SM Hamilton AD 《Organic & biomolecular chemistry》2006,4(3):482-492
A series of imidazole-containing peptidomimetic PFTase inhibitors and their co-crystal structures bound to PFTase and FPP are reported. The structures reveal that the peptidomimetics adopt a similar conformation to that of the extended CVIM tetrapeptide, with the imidazole group coordinating to the catalytic zinc ion. Both mono- and bis-imidazole-containing derivatives, 13 and 16, showed remarkably high enzyme inhibition activity against PFTase in vitro with IC50 values of 0.86 and 1.7 nM, respectively. The peptidomimetics were also highly selective for PFTase over PGGTase-I both in vitro and in intact cells. In addition, peptidomimetics and were found to suppress tumor growth in nude mouse xenograft models with no gross toxicity at a daily dose of 25 mg kg(-1). 相似文献