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991.
Matsunaga S Yoshida T Morimoto H Kumagai N Shibasaki M 《Journal of the American Chemical Society》2004,126(28):8777-8785
Full details of a direct catalytic asymmetric Mannich-type reaction of a hydroxyketone using a Et2Zn/(S,S)-linked-BINOL complex are described. By choosing the proper protective groups on imine nitrogen, either anti- or syn-beta-amino alcohol was obtained in good diastereomeric ratio, yield, and excellent enantiomeric excess using the same zinc catalysis. N-Diphenylphosphinoyl (Dpp) imine 3 gave anti-beta-amino alcohols in anti/syn = up to >98/2, up to >99% yield, and up to >99.5% ee, while Boc-imine 4 gave syn-beta-amino alcohols in anti/syn = up to 5/95, up to >99% yield, and up to >99.5% ee. The high catalyst turnover number (TON) is also noteworthy. Catalyst loading was successfully reduced to 0.02 mol % (TON = up to 4920) for the anti-selective reaction and 0.05 mol % (TON = up to 1760) for the syn-selective reaction. The Et2Zn/(S,S)-linked-BINOL complex exhibited far better TON than in previous reports of catalytic asymmetric Mannich-type reactions. Mechanistic studies to clarify the reason for the high catalyst efficiency as well as transformations of Mannich adducts are also described. 相似文献
992.
Lee SH Yoshida K Matsushita H Clapham B Koch G Zimmermann J Janda KD 《The Journal of organic chemistry》2004,69(25):8829-8835
Primary ureas have been used as substrates in rhodium-catalyzed N-H insertion reactions with an array of diazocarbonyls. The insertion reaction is efficient and gives excellent selectivity and yields. The products from the insertion reaction with diazoketones cyclize readily in the presence of acid to yield the corresponding imidazolones that can be further derivatized by N-alkylation with alkyl, allyl, and benzyl halides. Alternatively, the imidazolones were treated with phosphorus oxybromide to form the corresponding 2-bromoimidazoles that were further functionalized using a Suzuki coupling reaction. 相似文献
993.
Shigehiro Kagaya Zanariah Abdul Malek Yasuko Araki Kiyoshi Hasegawa 《Analytical sciences》2002,18(8):923-926
By applying an internal standardization, we could use a rapid coprecipitation technique using lanthanum phosphate as a coprecipitant for preconcentration of iron(III) and lead in their flame atomic absorption spectrometric determination. Indium as an internal standard was added to the initial sample solution together with lanthanum and phosphoric acid; the coprecipitation of iron(III) and lead was then carried out at pH about 3. After measuring the atomic absorbances of iron, lead, and indium in the final sample solution, we determined the contents of iron(III) and lead in the original sample solution by using the internal standardization with indium. In this method, complete collection of the precipitate was not required after the coprecipitation of iron(III), lead, and indium, because the ratio of the recovery of iron(III) or lead to that of indium was almost constant regardless of the recovery of the precipitate. This method was simple and rapid, and was available for the determination of 2-300 micrograms L-1 of iron(III) and 5-400 micrograms L-1 of lead in some water samples. 相似文献
994.
Maekawa Y Inaba T Hobo H Narita T Koshikawa H Moon S Kato J Yoshida M 《Chemical communications (Cambridge, England)》2002,(18):2088-2089
Radiation-induced reactions of cinnamic acid derivatives have been examined and compared with photoreactions in the crystalline state; all the reaction products were exactly the same as those of the photoreactions, indicating that the reactions proceed only via the lowest excited state to give [2 + 2] cycloadducts, E/Z isomerization products, or starting molecules. 相似文献
995.
Shiomi K Breedlove BK Kitayama H Nishioka T Kinoshita I Koga N Isobe K 《Chemical communications (Cambridge, England)》2002,(16):1756-1757
The parallel thiosulfite ligand (SSO2) in a rhodium complex, which is formed by oxygenation of a bridging disulfide, is converted to a bridging hydrocarbyl thiolate ligand and sulfur dioxide gas by the reaction with hydrocarbyl halides. 相似文献
996.
Tanaka R Yano T Nishioka T Nakajo K Breedlove BK Kimura K Kinoshita I Isobe K 《Chemical communications (Cambridge, England)》2002,(16):1686-1687
The novel thia-calix[n]pyridines (n = 3, 4, 6) coordinated to copper ions through nitrogen and sulfur atoms to give multinuclear complexes whose structures have been determined by X-ray crystallography and NMR spectra. 相似文献
997.
998.
This work performed fundamental studies for the extraction of gallium(III) with 2-methyl-8-quinolinol (HMQ) and 2-methyl-5-butyloxymethyl-8-quinolinol (HMO(4)Q) into supercritical carbon dioxide (SF-CO(2)) from a weakly acidic solution. The distribution constants of HMO(4)Q between aqueous and SF-CO(2) phases were determined at 45 degrees C, 8.6-20.4 MPa and I=0.1 M (H, Na)NO(3) (M=mol dm(-3)). At 45 degrees C and 15.7 MPa, gallium(III) was hardly extracted with HMQ into SF-CO(2), but was quantitatively extracted with HMO(4)Q in the pH range of 2.20-2.84. The extraction constant, K(ex, SF-CO(2)) (=[Ga(OH)(MO(4)Q)(2)](SF-CO(2))[H(+)](3)[Ga(3+)](-1)[HMO(4)Q](SF-CO(2))(-2)), of gallium(III) with HMO(4)Q was determined to be 10(-2.6+/-0.1) at 45 degrees C, 15.7 MPa and I=0.1 M (H, Na)NO(3), which was 63 times larger than that in heptane at 45 degrees C and 0.10 MPa. It was also found that the addition of 3,5-dichlorophenol as a synergist enhanced the extractability of gallium(III) with HMO(4)Q into SF-CO(2). 相似文献
999.
de la Cruz L Nguyen TH Ozawa K Shin J Graham B Huber T Otting G 《Journal of the American Chemical Society》2011,133(47):19205-19215
The two-component dengue virus NS2B-NS3 protease (DEN NS2B-NS3pro) is an established drug target, but inhibitor design is hampered by the lack of a crystal structure of the protease in its fully active form. In solution and without inhibitors, the functionally important C-terminal segment of the NS2B cofactor is dissociated from DEN NS3pro ("open state"), necessitating a large structural change to produce the "closed state" thought to underpin activity. We analyzed the fold of DEN NS2B-NS3pro in solution with and without bound inhibitor by nuclear magnetic resonance (NMR) spectroscopy. Multiple paramagnetic lanthanide tags were attached to different sites to generate pseudocontact shifts (PCS). In the face of severe spectral overlap and broadening of many signals by conformational exchange, methods for assignment of (15)N-HSQC cross-peaks included selective mutation, combinatorial isotope labeling, and comparison of experimental PCSs and PCSs back-calculated for a structural model of the closed conformation built by using the structure of the related West Nile virus (WNV) protease as a template. The PCSs show that, in the presence of a positively charged low-molecular weight inhibitor, the enzyme assumes a closed state that is very similar to the closed state previously observed for the WNV protease. Therefore, a model of the protease built on the closed conformation of the WNV protease is a better template for rational drug design than available crystal structures, at least for positively charged inhibitors. To assess the open state, we created a binding site for a Gd(3+) complex and measured paramagnetic relaxation enhancements. The results show that the specific open conformation displayed in the crystal of DEN NS2B-NS3pro is barely populated in solution. The techniques used open an avenue to the fold analysis of proteins that yield poor NMR spectra, as PCSs from multiple sites in combination with model building generate powerful information even from incompletely assigned (15)N-HSQC spectra. 相似文献
1000.
Hattori R Yamada K Hasegawa K Ishikawa Y Ito Y Sakamoto Y Yoshida N 《Rapid communications in mass spectrometry : RCM》2008,22(21):3410-3414
The isotope ratios of ethanol, an important constituent or ingredient of some foods and various beverages and fuels, provide information about biological and geographical origin and quality. We have developed an improved method for measuring the isotope ratio of ethanol in various samples by gas chromatography-high temperature conversion or combustion-isotope ratio mass spectrometry (GC-TC/C-IRMS) with headspace solid-phase microextraction (HS-SPME). A HS-SPME method was developed by optimizing several different parameters, including salt addition, incubation temperature and time, and extraction time. The HS-SPME method enabled us to determine the isotope ratio at low ethanol concentrations (0.08 mM) in 50 min with good precision (+/-0.3 per thousand for delta(13)C and +/-5 per thousand for deltaD). An advantage of this technique is that it can be adapted for use with samples which have high viscosity and contain many matrix compounds, such as alcoholic and non-alcoholic beverages. 相似文献