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991.
A robust method based on high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection has been developed
for simultaneous determination of six important ginsenosides (Rg1, Re, Rb1, Rc, Rb2, and Rd) in pharmaceutical preparations.
For sample preparation, simple and efficient extraction by ultrasonication, combined with solid-phase extraction (SPE) for
clean-up, was effective without consuming large amounts of solvent. Chromatographic separation was performed on an ODS column
with optimized gradient elution by means of a dual-solvent-pumping system. The validated method results in excellent separation,
and quantitative determination is highly precise and accurate. The problem of co-elution of ginsenosides Rg1 and Re is also
solved, with good resolution (RS approx. 1.5). Intraday variation was between 0.2 and 4.4% and interday variation was between 0.4 and 6.5% (n=5 for both). The accuracy was satisfactory—in the range 93.9 to 103.4% from replicate evaluation at three different spiking
concentrations. Overall limits of detection based on a typical injection volume of 5 μL were from 1.16 to 1.58 ng μL−1. The validated method enabled complete assessment for quality control of ginseng samples. The technique may be performed
with less sample preparation and, consequently, reduced possibility of sample loss. 相似文献
992.
Kazuhiko Sakaguchi Masahiro Yamamoto Takeshi Yamada Keiko Shimamoto 《Tetrahedron letters》2004,45(30):5869-5872
The synthesis of four types of optically active β-carbon-substituted analogs of threo-β-hydroxy aspartate (THA) and a β-carbon-substituted analog of threo-β-benzyloxy aspartate (TBOA), which are potent blockers of excitatory amino acid transporters in the mammalian central nervous system, via the chirality-transferring ester-enolate Claisen rearrangement of α-acyloxytrialkylsilane is described. 相似文献
993.
994.
The reactions of aryl Grignard reagents with p- and m-bromochlorobenzenes catalyzed by non-ligated NiCl2 give selectively chlorobiphenyl derivatives. By the stepwise reaction, an unsymmetrical terphenyl was synthesized in a good yield. 相似文献
995.
Optical Review - Optical discs are being sought as low-cost, earth-friendly storage candidates in response to increasing data volumes. To increase the recording density of optical disc, analog... 相似文献
996.
997.
Abstract The influence of dopants on the threshold electric field for switching anti-ferroelectric liquid crystals was determined from the optical response curve obtained by using a triangular wave. The effect of dopant concentration on the transition temperatures of the mixtures with a host material was also investigated. The threshold electric field was diminished depending on (i) the chemical structure of the additive and (ii) increasing amounts of the additive. The upper limits of the temperature region of the S*C A phases also decreased with increasing amount of additive, and these phases disappeared at 40 mol% of additive in all cases. Compound (C) is the most effective with respect to the threshold electric field. It is a two ring compound and has a chiral part similar to that of the host antiferroelectric liquid crystal compound. 相似文献
998.
999.
1000.
Tomohiro Ichitsuka Ikko Takahashi Nagatoshi Koumura Kazuhiko Sato Sh Kobayashi 《Angewandte Chemie (International ed. in English)》2020,59(37):15891-15896
Aryl amines are important pharmaceutical intermediates among other numerous applications. Herein, an environmentally benign route and novel approach to aryl amine synthesis using dehydrative amination of phenols with amines and styrene under continuous‐flow conditions was developed. Inexpensive and readily available phenols were efficiently converted into the corresponding aryl amines, with small amounts of easily removable co‐products (i.e., H2O and alkanes), in multistep continuous‐flow reactors in the presence of heterogeneous Pd catalysts. The high product selectivity and functional‐group tolerance of this method allowed aryl amines with diverse functional groups to be selectively obtained in high yields over a continuous operation time of one week. 相似文献