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991.
Szabó LF 《Molecules (Basel, Switzerland)》2008,13(8):1875-1896
Strictosidine, the precursor of more than 2,500 indole alkaloids, was isolated from four species of three plant families. By searching the Dictionary of Natural Products on DVD it was found that about 150 indole alkaloids were obtained from the same species (coalkaloids), which is a direct proof of their common origin. On the base of their three-dimensional structure, taxonomic properties and standard reaction mechanisms an extended network was established which involved the four fundamental skeletons, the three types of carbon framework in the secologanin subunit and all major groups of indole alkaloids derived from secologanin and tryptamine (except a few minor groups, in which only less then 10 alkaloids were known). The system was extended to the heterodimer indole alkaloids and the quinoindole alkaloids as well. 相似文献
992.
993.
González Baró A Andersson I Pettersson L Gorzsás A 《Dalton transactions (Cambridge, England : 2003)》2008,(8):1095-1102
The speciation in the aqueous H(+)/H(2)VO(4)(-)/H(2)O(2)/maltol (Ma), H(+)/H(2)VO(4)(-)/uridine (Ur) and H(+)/H(2)VO(4)(-)/H(2)O(2)/Ur systems was determined in the physiological medium of 0.150 M Na(Cl) at 25 degrees C. A combination of quantitative (51)V NMR (Bruker AMX500) and potentiometric data (glass electrode) was collected and treated simultaneously by the computer program LAKE. In the quaternary maltol system, the two species VXMa(2)(-) and VX(2)Ma(2-) (where X denotes the peroxo ligand) were found in the pH region 5-10, in addition to all binary and ternary complexes. Their formation was fast. In the ternary uridine (H(+)/H(2)VO(4)(-)/Ur) subsystem, altogether three vanadate-uridine (V-Ur) species were found in the pH region 4-10, with compositions VUr(2-), V(2)Ur(2)(2-) and V(2)Ur(2)(3-). Equilibrium was fast except in weakly acidic solutions when slowly decomposing decavanadates formed. In the quaternary H(+)/H(2)VO(4)(-)/H(2)O(2)/Ur system, five additional species were found at pH > 7. They were of VXUr and VX(2)Ur compositions. Their formation was fast. Formation constants, compositions and (51)V NMR chemical shifts are given for all the species found in the systems, and equilibrium conditions are illustrated in distribution diagrams as well as the fit of the model to the experimental data. Biological and medical relevance of the species (in the treatment of diabetes) are also discussed, with pseudo-physiological conditions modelled. 相似文献
994.
Leroy F Miró P Poblet JM Bo C Bonet Avalos J 《The journal of physical chemistry. B》2008,112(29):8591-8599
The dynamics of Keggin polyoxoanions in aqueous solution in the presence of monovalent cations is analyzed through molecular dynamics simulations. Together with structural information yielding the radial distribution functions of Li(+), Na(+), and K(+) with three polyoxometalates (POMs) bearing 3-, 4-, and 5- charges, the diffusion coefficient of these POMs is calculated. We found that the effect of the microscopic molecular details of the solvent is a key aspect to interpreting the structural and dynamic data because a competition between electrostatic interactions between the ions and the stability of the solvation shell is established. Furthermore, we show that solvent-shared structures weakly bound to the POM anion play a crucial role in the determination of the dynamic properties of the anion. The nature of these ion pairs, structurally characterized for the first time, is consistent with experimental data available. 相似文献
995.
A mechanistically new palladium-pincer complex catalyzed allylation of sulfonimines is presented. This reaction involves C-H bond functionalization of allyl nitriles under mild conditions. The reaction proceeds with a high regioselectivity, without allyl rearrangement of the product. Modeling studies indicate that the carbon-carbon bond formation process proceeds via (eta (1)-allyl)palladium pincer complex intermediates. 相似文献
996.
An efficient palladium pincer-complex catalyzed reaction has been developed for alpha-C-H bond functionalization of benzyl nitriles. The studied coupling reaction with sulfonylimines affords beta-aminonitriles with usually high levels of stereoselectivity. The stereoselectivity of the process is highly dependent on the electronic effects of the ortho substituents of the benzyl moiety. Promising levels of enantiomeric excess are obtained using chiral pincer complexes as catalysts. 相似文献
997.
The viability of the toluate moiety as a radical precursor has been examined by studying deoxygenation and cyclization reactions. 相似文献
998.
Allylsilane and various vinyl substrates undergo selective C-H bond functionalization based boronation reactions using iridium catalysis. The products were further reacted with aryl and vinyl halogenides in a one-pot sequence. This method is suitable for regio- and stereoselective synthesis of various allylsilanes and dienylsilanes. 相似文献
999.
Pérez-Nueno VI Ritchie DW Borrell JI Teixidó J 《Journal of chemical information and modeling》2008,48(11):2146-2165
HIV entry inhibitors have emerged as a new generation of antiretroviral drugs that block viral fusion with the CXCR4 and CCR5 membrane coreceptors. Several small molecule antagonists for these coreceptors have been developed, some of which are currently in clinical trials. However, because no crystal structures for the coreceptor proteins are available, the binding modes of the known inhibitors within the coreceptor extracellular pockets need to be analyzed by means of site-directed mutagenesis and computational experiments. Previous studies have indicated that there is more than one binding site within the CCR5 extracellular pocket. This article investigates and develops this hypothesis using a novel spherical harmonic-based consensus shape clustering approach. The consensus shape approach is evaluated using retrospective virtual screening of CXCR4 and CCR5 inhibitors. Multiple combinations of CCR5 ligands in multiple trial superpositions are constructed to find consensus queries that give high virtual screening enrichments. Receiver-operator-characteristic performance analyses for both CXCR4 and CCR5 inhibitors show that the new consensus shape matching approach gives better virtual screening enrichments than existing shape matching and docking virtual screening techniques. The results obtained also provide strong evidence to support the notion that there are three main binding sites within the CCR5 extracellular cavity. 相似文献
1000.
Santana Rodríguez JJ Sosa Ferrera Z Vega Moreno D Torres Padrón ME Mahugo Santana C 《Analytical and bioanalytical chemistry》2008,391(3):725-733
The establishment of new analytical methods which improve quality and sensitivity in the determination of environmental pollutants
in liquid and solid samples is demanded. The use of micellar systems have become an advantageous tool for the extraction of
pollutant compounds, due to their easy handling, biodegradability, and the one-step procedure, and they are compatible with
the hydroalcoholic mobile phases used in HPLC. The focus of this review is to present recently developed methods and the main
trends in the use of micellar media combined with solid-phase microextraction and solid-phase extraction in the chromatographic
analysis of organic compounds in different types of environmental matrix, including water, sediments, and biological samples.
Selected samples illustrate the benefits of these systems in the whole of analytical process. The advantages of micellar media
over conventional extractants are reduction of solvent usage, low cost, easy handling, and non-toxic procedure. 相似文献