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51.
First stereoselective total synthesis of naturally occurring bioactive cyclodepsipeptide alveolaride C has been achieved using a convergent approach. This synthetic study enabled us to establish unambiguously the stereochemistry of three unassigned chiral centres embedded in the nonpeptidic segment as well as revised the stereochemistry of the proposed β-phenylalanine counterpart of the molecule. The key strategic features of this synthesis include Sharpless asymmetric dihydroxylation for installing the vicinal diol moiety, Julia–Kocienski olefination for constructing the aliphatic side chain, the Shiina protocol for intermolecular esterification, amide coupling and macrolactamization for the ring formation.First total synthesis of natural cyclodepsipeptide alveolaride C has been accomplished with an unambiguous solution to its structural riddle. 相似文献
52.
This work integrates rapid techniques for mutation detection by producing single-stranded DNA and (renatured) double-stranded DNA on-chip, labeling these with fluorescent DNA stains and then performing two complementary methods of mutation detection-single stranded conformation polymorphism (SSCP) analysis and heteroduplex analysis (HA). This involves the denaturation of double-stranded polymerase chain reaction (PCR) product into single-stranded DNA, the mutation analysis of the single-stranded DNA by SSCP and the rehybridized double-stranded DNA by HA. These steps were performed entirely on-chip within several minutes of operation. The combination of these two mutation detection methods on-chip provides a highly sensitive method of mutation detection for either genotyping or screening. Many mutation analysis methods rely upon fluorescently labeled samples from a PCR with fluorescently labeled primers. By labeling on-chip we not only attain improved signal strength, but the method is considerably more versatile. Although we used PCR products in this work, this method could be used to analyze DNA from any source. We believe that this combination of several procedures on a single chip represents a significant step in the development of higher levels of integration upon microfluidic devices. 相似文献
53.
Beomsue Kim Masahiro Fukuda Jung‐Yeol Lee Dongdong Su Srikanta Sanu Aymeric Silvin Audrey T. T. Khoo Taejoon Kwon Xiao Liu Weijie Chi Xiaogang Liu Sejong Choi Diana S. Y. Wan Sung‐Jin Park Jin‐Soo Kim Florent Ginhoux H. Shawn Je Young‐Tae Chang 《Angewandte Chemie (International ed. in English)》2019,58(24)
54.
55.
Karan Singh Vinayak Suneel Kumar 《The European Physical Journal A - Hadrons and Nuclei》2012,48(7):1-7
One-neutron knockout reactions in a 9Be target have been investigated at relativistic energies, near 700 MeV/u, for a set of sd-shell, neutron-rich nuclei. The experiment was performed in the FRS spectrometer, at GSI. ??-ray measurements were carried out by means of the MINIBALL ??-ray spectrometer and allowed the determination of partial cross-sections and branching ratios corresponding to the final states of the emerging knockout fragments. Experimental results are presented for 17C, 19N, 21O and 25F projectiles. The role of excited states of the N ? 1 fragments in the composition of the ground state of these neutron-rich projectiles is outlined in this work. 相似文献
56.
Costunolide and dehydrocostus lactone are two guianolide sesquiterpene lactones present in abundance in Saussurea costus, a plant popularly known as `costus' and renowned throughout the world for its medicinal properties. A simple densitometric
TLC method for simultaneous quantification of costunolide and dehydrocostus lactone, without derivatization, has been developed
as an alternative to gas chromatography. The method enables rapid, sensitive, and reproducible simultaneous analysis of a
variety of samples. The method was validated for precision, repeatability, and accuracy in accordance with ICH guidelines.
Amounts of costunolide and dehydrocostus lactone in different samples of costus, estimated by use of this method, were in
the range 0.46 to 1.00% and 0.81 to 1.21%, respectively. The proposed method is simple, precise, specific, sensitive, and
accurate and can be used by the herbal drug industry for routine quality control of the crude drug costus. 相似文献
57.
The present work reports the application of the WCl6–e?–Al–CH2Cl2 catalyst system to the ring‐opening metathesis polymerization of norbornene. Analysis of the polynorbornene microstructure by means of 1H and 13C NMR spectroscopy indicates that the polymer contains a mainly cis stereoconfiguration of the double bonds (σc = 0.61) and a blocky distribution (rtrc > 1) of cis and trans double bonds (rtrc = 3.37). This catalytic system is reluctant to facilitate the competing addition reactions of cycloalkenes while proceeding with the polymerization reactions with good conversions and at short periods. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
58.
Magnetic proximity effects can lead to novel phenomena in the transport properties of topological insulators. In this study, we demonstrate a characteristic fourfold symmetry in the angular dependence of magnetoresistance in the topological insulator BiSbTeSe2 exfoliated onto magnetic insulator yttrium iron garnet substrates. The observed symmetry is seen to arise when the external magnetic field is in‐plane to the current direction and gets enhanced at large field magnitudes. Increasing the temperature and current density diminishes the fourfold symmetry. The symmetry seems to be a signature of the proximity effect from the underlying magnetic substrate on BiSbTeSe2. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
59.
Poonam Kumari Sumit Sood Anil Kumar Karan Singh 《Journal of heterocyclic chemistry》2020,57(2):796-804
The synthesis of 4-formylpyrazoles using Vilsmeier-Haack reagent is a common protocol in pyrazole chemistry. An efficient microwave-assisted synthesis of 4-formylpyrazoles by employing Vilsmeier-Haack reagent (OPC-VH) derived from phthaloyl dichloride/dimethylformamide has been described. This method offers the advantages of operational simplicity, avoiding the use of POCl3 as toxic reagents and reuse of the by-product in the preparation of phthaloyl dichloride. 相似文献
60.
Karan Arora 《合成通讯》2014,44(24):3552-3562
Synthesis of novel bicyclo[2.2.2]octenones endowed with a β,γ-enone system in which γ-carbon is substituted with an electron-withdrawing group from simple aromatics is described. Oxa-di-pi-methane reaction of bicyclo[2.2.2]octenones to functionalized bicyclo[3.3.0]octanes and their transformation to bicyclo[3.2.1]octane framework are also presented. 相似文献