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81.
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Sudhir Kashyap 《Tetrahedron letters》2007,48(51):8960-8962
C-2 Methylene glycosides were synthesized from C-2 propargyloxymethyl glycals in a stereoselective manner using a catalytic quantity of AuCl3. The Au-catalyzed reaction was explored using various aglycones. The current protocol enables the preparation of C-2 methylene glycosides, tolerates diverse functional groups and is fast, catalytic and mild. 相似文献
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This paper describes validated high-performance column liquid chromatographic (HPLC) and high-performance thin-layer chromatographic (HPTLC) methods for simultaneous estimation of acetylsalicylic acid (ASA) and clopidogrel bisulfate (CLP) in pure powder and formulations. The HPLC separation was achieved on a Nucleosil C8 column (150 mm length x 4.6 mm id, 5 microm particle size) using acetonitrile-phosphate buffer, pH 3.0 (55 + 45, v/v) mobile phase at a flow rate of 1.0 mL/min at ambient temperature. The HPTLC separation was achieved on an aluminum-backed layer of silica gel 60F254 using ethyl acetate-methanol-toluene-glacial acetic acid (5.0 + 1.0 + 4.0 + 0.1, v/v/v/v) mobile phase. Quantitation was achieved with UV detection at 235 nm over the concentration range 4-24 microg/mL for both drugs, with mean recoveries of 99.98 +/- 0.28 and 100.16 +/- 0.66% for ASA and CLP, respectively, using the HPLC method. Quantitation was achieved with UV detection at 235 nm over the concentration range of 400-1400 ng/spot for both drugs, with mean recoveries of 99.93 +/- 0.55 and 100.21 +/- 0.83% for ASA and CLP, respectively, using the HPTLC method. These methods are simple, precise, and sensitive, and they are applicable for the simultaneous determination of ASA and CLP in pure powder and formulations. 相似文献
86.
The stepwise addition of thiophenol to benzoquinone gives thiophenylbenzoquinone (1b), 2,5-and 2,6-di-(thiophenyl)benzoquinone (2,3),2,3,6-tri(thiophenyl)benzoquinone (4) and 2,3,5,6-tetra(thiophenyl)benzoquinone. (5). Compounds1–4 can be crystallized, and the13C NMR spectra are readily interpreted. Compound5 could not be crystallized easily, and the NMR showed more than twice as many lines as the number of carbon atoms. Slow evaporation in an NMR tube produced three distinct crystals. X-ray analysis of two crystals (5a and5c) showed the compounds to be conformational polymorphs. Direct synthesis of5 from tetrachlorobenzoquinone and thiophenol yielded only conformer5a, and the13C NMR spectrum showed only the 6 lines expected for four equivalent phenyl substituents on benzoquinone. Subjecting5a to a variety of solvents, reagents and temperatures did not regenerate the original13C NMR spectrum. The crystal structures, conformations, and polymorphs are discussed. 相似文献
87.
M. E. Vieira Segatto F. N. Timofeev R. Wyatt R. Kashyap J. R. Taylor 《Optics Communications》2001,190(1-6):165-171
We demonstrate transmission of two wavelength division multiplexed (WDM) bit parallel channels over 100 km of standard single mode fibre link using direct-modulated laser diodes at 10 Gbit/s channel. Step-chirped fibre gratings are used to simultaneously compensate to bit skew and dispersion. Bit skew of approximately 2.5 ns due to the fibre dispersion is completely compensated. Our work show shows that the step-chirped fibre grating technique can eliminate the bit skew for bit parallel WDM systems operating at Gbit rate over hundreds of kilometres of fibre link. 相似文献
88.
We consider theoretically a mechanism for laser cooling in rare-earth-doped low-phonon materials based simultaneously on two cooling cycles: a traditional cooling cycle with an anti-Stokes fluorescence transition as well as an infrared-to-visible upconversion cycle, to overcome the self-termination effects in either anti-Stokes or upconversion cooling on its own. Our simulations, performed for erbium-doped potassium-lead chloride crystal (Er3+:KPl2Cl5) known to be an extremely low phonon energy host, uses two pump wavelengths corresponding to the long wavelength tails of the absorption spectra of the 4I15/2 → 4I13/2 and 4I15/2 → 4I9/2 transitions. The contribution of each pump source to the cooling process is comprehensively investigated. We show that, although the energy gap between 4I15/2 and 4I9/2 levels exceeds the energy gap between 4I15/2 and 4I13/2 levels and cooling process is more efficient with the cycle based on the 4I15/2 → 4I13/2 transition, the second cooling cycle based on the 4I15/2 → 4I9/2 transition can be used as a supplementary one. 相似文献
89.
Shah Dimal A. Rana Jainika P. Baldania Sunil L. Chhalotiya Usmangani K. Bhatt Kashyap K. 《平面色谱法杂志一现代薄层色谱法》2014,27(1):52-57
JPC – Journal of Planar Chromatography – Modern TLC - A simple, sensitive, and precise high-performance thin-layer chromatographic method has been developed for the estimation of... 相似文献
90.
DMAP was found to accelerate significantly the rate of Pd(OAc)2 catalyzed Barbier type allylation of carbonyl compounds by allylbromide using SnCl2·2H2O as reducing agent. Both aldehyde as well as ketones produced excellent yields within a short reaction time in the presence of 3 mol % of Pd(OAc)2 and 12 mol % of DMAP at room temperature. Aldehydes could be allylated within 5–10 min whereas, in case of ketones, the reaction completes in 45–120 min. 相似文献