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991.
Compared with a standard gradient system, the new gradient system which we developed has a major advantage because it permits a wide range of acetonitrile content, e.g. more than the critical threshold, in the polypeptide solution and allows the quantitative analysis of the polypeptide with satisfactory analytical precision. Additionally, this new gradient system allows the enhancement of the sensitivity of the polypeptide analysis proportionate to the increased volume of solution loaded with the same levels of precision. In contrast, when using a standard gradient system it is difficult to analyze a polypeptide quantitatively with good precision due to either adsorption to various materials or to irregular change in the ratio between a retained and a passed peak of the polypeptide. Additionally, the appearance of a passed peak results in a loss in the sensitivity of the polypeptide analysis, although no adsorption of a polypeptide to various materials occurs in a solution with acetonitrile content more than the critical threshold. Consequently, the new gradient system is effective for the simultaneous and quantitative analysis of different polypeptides with good precision and without any loss of sensitivity due to either adsorption to various materials or the appearance of a passed peak. 相似文献
992.
I. M. Chung M. Ali S. C. Chun K. Y. San C. A. M. Peebles A. Ahmad 《Chemistry of Natural Compounds》2008,44(4):458-462
Two new compounds catharanthusopimaranoside A (1) and catharanthusopimaranoside B (2) along with three known compounds have been isolated from the hairy root cultures of Catharanthus roseus. Their structures have been elucidated with the help of 500 MHz NMR using 1D and 2D spectral methods viz: NMR, 1H-1H COSY, 1H-13C HETCOR, etc., and DEPT aided by EIMS, FABMS, and IR spectroscopy.
__________
Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 369–372, July–August, 2008. 相似文献
993.
F. Belzunce J. F. Pinar J. M. Ruiz 《Annals of the Institute of Statistical Mathematics》2005,57(4):803-815
In this paper we develop a new family of tests for the dilation order based in a characterization of the dilation order. This
family of tests statistics can be used for testing the exponentiality against HNBUE (HNWUE) alternatives. Asymptotic distributional
results are given for both families of tests. For the HNBUE (HNWUE) we also derive the exact distribution under the null hypothesis.
Supported by Ministerio de Ciencia y Tecnologia under Grant BFM2003-02497/MATE.
Supported by Fundación Séneca (CARM). 相似文献
994.
4-(2-N(1)-tosyl-N(3)-methyl-4-,4-dimethylimidazolidyl)-3-ketobutanoate reacts with tryptamine, in the presence of acetic acid, to give primary “carbon transfer” products, which can be conveniently converted to synthetically useful indole and dihydroindole derivatives. 相似文献
995.
Iron‐Catalyzed Cross‐Couplings in the Synthesis of Pharmaceuticals: In Pursuit of Sustainability
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《Angewandte Chemie (International ed. in English)》2018,57(35):11116-11128
The scarcity of precious metals has led to the development of sustainable strategies for metal‐catalyzed cross‐coupling reactions. The establishment of new catalytic methods using iron is attractive owing to the low cost, abundance, ready availability, and very low toxicity of iron. In the last few years, sustainable methods for iron‐catalyzed cross‐couplings have entered the critical area of pharmaceutical research. Most notably, iron is one of the very few metals that have been successfully field‐tested as highly effective base‐metal catalysts in practical, kilogram‐scale industrial cross‐couplings. In this Minireview, we critically discuss the strategic benefits of using iron catalysts as green and sustainable alternatives to precious metals in cross‐coupling applications for the synthesis of pharmaceuticals. The Minireview provides an essential introduction to the fundamental aspects of practical iron catalysis, highlights areas for improvement, and identifies new fields to be explored. 相似文献
996.
Generation of Aryl and Heteroaryl Magnesium Reagents in Toluene by Br/Mg or Cl/Mg Exchange
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Dorothée S. Ziegler Prof. Dr. Konstantin Karaghiosoff Prof. Dr. Paul Knochel 《Angewandte Chemie (International ed. in English)》2018,57(22):6701-6704
The alkylmagnesium alkoxide sBuMgOR?LiOR (R=2‐ethylhexyl), which was prepared as a 1.5 m solution in toluene, undergoes very fast Br/Mg exchange with aryl and heteroaryl bromides, producing aryl and heteroaryl magnesium alkoxides (ArMgOR?LiOR) in toluene. These Grignard reagents react with a broad range of electrophiles, including aldehydes, ketones, allyl bromides, acyl chlorides, epoxides, and aziridines, in good yields. Remarkably, the related reagent sBu2Mg?2 LiOR (R=2‐ethylhexyl) undergoes Cl/Mg exchange with various electron‐rich aryl chlorides in toluene, producing diorganomagnesium species of type Ar2Mg?2 LiOR, which react well with aldehydes and allyl bromides. 相似文献
997.
Lun An Yu‐Lan Xiao Prof. Dr. Shu Zhang Prof. Dr. Xingang Zhang 《Angewandte Chemie (International ed. in English)》2018,57(23):6921-6925
Although iron‐catalyzed cross‐coupling of Grignard reagents with alkyl halides has been well established, the adoption of the reaction for fluoroalkylations has not been reported because traditional catalytic systems often lead to defluorination reactions. Described herein is the investigation of an iron‐catalyzed cross‐coupling between arylmagnesium bromides and difluoroalkyl bromides with modified N,N,N′,N′‐tetramethyl‐ethane‐1,2‐diamine (TMEDA) as a ligand. The use of this bulky diamine, in which a butylene is substituted at one carbon atom of the ethylene backbone in TMEDA, enables the iron‐catalyzed difluoroalkylation under mild reaction conditions with a wide range of difluoroalkyl bromides, including vulnerable bromodifluoromethane, thus providing a general and cost‐efficient route for applications in medicinal chemistry. 相似文献
998.
Christian Fischer Prof. Dr. Christof Sparr 《Angewandte Chemie (International ed. in English)》2018,57(9):2436-2440
Despite the manifold use of heterocyclic fluorophores, only a fraction of the desired dye diversity can be accessed by contemporary synthetic approaches. Herein, we describe a modular method that converts various carboxylic acid esters directly into a broad spectrum of heteroanthrylium fluorophores. The double addition of heteroatom‐bridged 1,5‐bifunctional organomagnesium reagents to esters leads to the formation of acridinium, xanthylium, and SiR fluorophores after dehydrative acidic work‐up. This one‐step synthetic method provides access to organophotoredox catalysts for dual catalysis with nickel and dyes amenable to fluorescence enhancement. 相似文献
999.
SuFEx Chemistry of Thionyl Tetrafluoride (SOF4) with Organolithium Nucleophiles: Synthesis of Sulfonimidoyl Fluorides,Sulfoximines, Sulfonimidamides,and Sulfonimidates
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Dr. Bing Gao Dr. Suhua Li Dr. Peng Wu Dr. John E. Moses Dr. K. Barry Sharpless 《Angewandte Chemie (International ed. in English)》2018,57(7):1939-1943
Thionyl tetrafluoride (SOF4) is a valuable connective gas for sulfur fluoride exchange (SuFEx) click chemistry that enables multidimensional linkages to be created via sulfur–oxygen and sulfur–nitrogen bonds. Herein, we expand the available SuFEx chemistry of SOF4 to include organolithium nucleophiles, and demonstrate, for the first time, the controlled projection of sulfur–carbon links at the sulfur center of SOF4‐derived iminosulfur oxydifluorides (R1?N=SOF2). This method provides rapid and modular access to sulfonimidoyl fluorides (R1?N=SOFR2), another array of versatile SuFEx connectors with readily tunable reactivity of the S?F handle. Divergent connections derived from these valuable sulfonimidoyl fluoride units are also demonstrated, including the synthesis of sulfoximines, sulfonimidamides, and sulfonimidates. 相似文献
1000.
A Highly efficient route for the synthesis of 1,2-disubstituted acetylene derivatives has been developed by palladium catalyzed cross-couplings of alkynyl halides with (hetero)aryl aluminium reagents under mild conditions. This has given corresponding cross-coupling products good to excellent isolated yields of up to 99%. The aryls bearing electron-donating or electron-withdrawing groups in either alkynylhalides or arylaluminum substrates gave cross-coupling products good yields. This process was simple and easily performed, which provides an efficient method for the synthesis of 1,2-disubstituted acetylenes derivatives. On the basis of the experimental results, a possible catalytic cycle has been proposed. 相似文献