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191.
Introduction of carbohydrate auxiliary into enanine-based catalyst provided a novel enantiocontrol for aqueous aldol reaction. Methyl 2-(l-prolyl)amido-2-deoxy-α-d-glucopyranosides led to the enantiocontrol as parent amino acids did in the reaction of acetone with 4-nitrobenzaldehyde, and provided R-aldol in an improved efficiency compared with that of l-proline in aqueous media. The enantioreversal control of that with parent amino acid was observed in the reaction with methyl 2-(l-tert-leucyloxy)-α-d-glucopyranoside, which provided S-aldol predominantly in moderate efficiency. The novel enantiocontrol system was proposed to occur as a result of the generation of the transition state through the reaction of enamine with hydroxyl group on glucoside auxiliary. 相似文献
192.
Lee XP Kumazawa T Fujishiro M Hasegawa C Arinobu T Seno H Ishii A Sato K 《Journal of mass spectrometry : JMS》2004,39(10):1147-1152
Paraquat (PQ) and diquat (DQ) in human whole blood and urine were analyzed by high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) with positive ion electrospray ionization (ESI). The compounds were extracted with Sep-Pak C18 cartridges from whole blood and urine samples containing ethyl paraquat as an internal standard. The separation of PQ and DQ was carried out using ion-pair chromatography with heptafluorobutyric acid in 20 mM ammonium acetate and acetonitrile gradient elution for successful coupling with MS. Both compounds formed base peaks due to [M-H]+ ions by HPLC/ESI-MS and the product ions produced from each [M-H]+ ion by HPLC/MS/MS. Selective reaction monitoring (SRM) showed much higher sensitivity for both body fluids. Therefore, a detailed procedure for the detection of compounds by SRM with HPLC/MS/MS was established and carefully validated. The recoveries of PQ and DQ were 80.8-95.4% for whole blood and 84.2-96.7% for urine. The calibration curves for PQ and DQ showed excellent linearity in the range of 25-400 ng ml(-1) of whole blood and urine. The detection limits were 10 ng ml(-1) for PQ and 5 ng ml(-1) for DQ in both body fluids. The intra- and inter-day precision for both compounds in whole blood and urine samples were not greater than 13.0%. The data obtained from the determination of PQ and DQ in rat blood after oral administration of the compounds are also presented. 相似文献
193.
Stanislaw Dzwigaj Masaya Matsuoka Masakazu Anpo Michel Che 《Research on Chemical Intermediates》2003,29(7-9):665-680
VxSiβ catalysts with x=0.05, 0.2 and 1.75 V wt%, prepared by a two-step post-synthesis method, have been characterised by physical techniques and their photocatalytic reactivity investigated in the decomposition of NO. XRD and diffuse reflectance UV-Vis spectroscopy show that vanadium is incorporated as tetrahedral Vv species, a result confirmed by XANES and EXAFS. Photoluminescence spectra of V x Siβ catalysts show well-resolved vibrational fine structures due to three different kinds of tetrahedral VV (α, β, γ) species, with different degrees of distortion. Their relative amounts depend on V content and calcination/hydration treatments. Calcined-hydrated V1.75Siβ, calcined V1.75Siβ and calcined V0.05Siβ exhibit mainly the α, γ and β kind of tetrahedral vanadium, respectively. These samples are active in the decomposition of NO under UV-irradiation, leading mainly to N2 and O2. The decomposition of NO is strongly enhanced in presence of propane, leading to higher yield of N2. The latter strongly depends on the distortion of tetrahedral V species. The highest activity is found for the catalyst with tetrahedral V of highest distortion, lowest V=O bond length and biggest lifetime of its excited triplet state. 相似文献
194.
For the purpose of exploring a new reaction of acylzirconocene chloride as an acyl anion donor, Cu(I)-catalyzed cross-coupling and conjugate addition reactions of acylzirconocene chloride were studied. The coupling reaction with allylic or propargylic halides efficiently proceeded to yield β,γ-unsaturated ketone or allenyl ketone derivatives, respectively. The conjugated addition reaction to ,β-enones was carried out in the presence of 2 equiv. of BF3·OEt2 giving 1,4-diketone compounds. 相似文献
195.
Kim Y Zhao F Mitsuishi M Watanabe A Miyashita T 《Journal of the American Chemical Society》2008,130(36):11848-11849
The paper describes a flexible approach to building up high-quality ultrathin SiO2 films under deep UV light irradiation at room temperature. The ultrathin hybrid nanosheet possessing polyoctahedral silsesquioxane (POSS) has been designed to prepare densely packed ultrathin POSS films by the Langmuir-Blodgett (LB) technique. The LB technique enables POSS to have a multilayered structure with nanoscale precision. The films' hardness and modulus changed considerably from 0.1 and 2.6 GPa to 1.7 and 32.2 GPa, respectively, after deep UV light irradiation. Subsequent FTIR measurements revealed that the organic components were removed completely and that the POSS cage structure turned to an Si-O-Si network structure. X-ray photon spectroscopy also confirmed high-quality SiO2 formation with no suboxides. 相似文献
196.
A versatile synthetic method for the preparation of the allenylboronates, Cu(I)-catalyzed reaction of propargylic carbonates with a diboron, is described. A Cu(O-t-Bu)-Xantphos catalyst system was effective for the preparation of various allenylboron compounds, allenylboronates with different substitution patterns, those with functional groups, and an axially chiral one. The Lewis acid promoted stereoselective addition to aldehydes leading to homopropargylic alcohols showed the usefulness of the new allenylboronates. 相似文献
197.
198.
Ochiai M Yoshimura A Mori T Nishi Y Hirobe M 《Journal of the American Chemical Society》2008,130(12):3742-3743
Reported here for the first time are the oxidative couplings of alkynes and primary alcohols yielding conjugated enones. Although the BF3-catalyzed reaction of terminal alkynes with p-trifluoromethylphenyl(difluoro)-lambda3-bromane results in the fluoro-lambda3-bromanation of triple bonds to afford (E)-beta-fluorovinyl-lambda3-bromanes, reaction of an alkyne with the difluoro-lambda3-bromane in the presence of an alcohol and BF3-Et2O affords directly conjugated enones in good yields. The reaction proceeds in a highly stereo- and regioselective manner under metal-free conditions. Interestingly, no formation of enones was detected, when difluoro-lambda3-iodane p-CF3C6H4IF2 was used instead of the lambda3-bromane. A mechanism involving a lambda3-bromane-induced oxidation of an alcohol to an aldehyde, [2 + 2] cyclization with alkynes yielding 2H-oxetes, and finally the electrocyclic ring opening is discussed. 相似文献
199.
Takemoto Y Watanabe H Uchida K Matsumura K Nakae K Tashiro E Shindo K Kitahara T Imoto M 《Chemistry & biology》2005,12(12):1337-1347
Cancer cell migration is a required step in cancer metastasis. We screened for inhibitors of cancer cell migration of microbial origin, and obtained moverastin, a member of the cylindrol family, from Aspergillus sp. F7720. However, the results of an NMR spectroscopic analysis raised the possibility that moverastin is a mixture of two diastereomers. Separation of the C-10 epimers of synthetic moverastin and a bioassay revealed that both diastereomers (moverastins A and B) had inhibitory effects on cell migration. Furthermore, we demonstrated that moverastins A and B inhibited FTase in vitro, and they also inhibited both the membrane localization of H-Ras and the activation of the PI3K/Akt pathway in EC17 cells. Thus, moverastins inhibited the migration of tumor cells by inhibiting the farnesylation of H-Ras, and subsequent H-Ras-dependent activation of the PI3K/Akt pathway. 相似文献
200.
Sangita Karanjit Masaya Kashihara Atsushi Nakayama Lok Kumar Shrestha Katsuhiko Ariga Kosuke Namba 《Tetrahedron》2018,74(9):948-954
A palladium(0) nanocluster supported on hydrotalcite has been prepared and tested for the Suzuki coupling reaction. The prepared catalyst showed very efficient catalytic activity for cross coupling of iodo- and bromoarenes under very mild reaction conditions, affording >90% yield. Under the optimized reaction conditions, chloroarenenes also showed very good reactivity. Transmission electron microscopic imaging data showed the formation of very small Pd(0)-nanoclusters (d = 2.2 ± 0.5 nm) well dispersed on the support, which enhanced the activity and stability of the catalyst for the Suzuki cross-coupling reaction. This catalytic system offers an easy method of preparation with good activity and reusability up to five cycles. 相似文献