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91.
Nagamitsu T Takano D Marumoto K Fukuda T Furuya K Otoguro K Takeda K Kuwajima I Harigaya Y Omura S 《The Journal of organic chemistry》2007,72(8):2744-2756
The total synthesis of borrelidin has been achieved. The best feature of our synthetic route is macrocyclization at C11-C12 for the construction of an 18-membered ring after esterification between two segments. A detailed examination of the macrocyclization led us to the samarium(II) iodide-mediated intramolecular Reformatsky-type reaction as the most efficient synthetic approach. The two key segments were synthesized through regioselective methylation, directed hydrogenation, stereoselective Reformatsky-type reaction, and MgBr2.Et2O-mediated chelation-controlled allylation. 相似文献
92.
Takeda Y Isai N Masuda T Honda G Takaishi Y Ito M Otsuka H Ashurmetov OA Khodzhimatov OK 《Chemical & pharmaceutical bulletin》2001,49(8):1039-1041
From the aerial parts of Phlomis spinidens, two new flavonol bisglycosides, phlomisflavosides A (1) and B (2), were isolated together with the known compounds, astragalin, isoquercitrin, lamiridoside, phlomoside A, shanzhiside methyl ester, 8-O-acetylshanzhiside methyl ester, phlorigidoside C, rodioloside (=salidroside), forsythoside B, citroside A and lariciresinol-4'-O-beta-D-glucoside. The structures of the new compounds were elucidated based on spectral and chemical evidence. 相似文献
93.
H Terao T Sugawara Y Kita N Sato E Kaho S Takeda 《Journal of the American Chemical Society》2001,123(43):10468-10474
The crystal structure of a hydrated crystal of bis(squaryl)biphenyl (BSQB*4H2O), in which two squaric acid moieties are connected with a 4,4'-biphenyl unit, was characterized by the presence of a one-dimensional hydrogen-bonded chain composed of BSQB and water molecules. X-ray crystallographic analysis showed that BSQB exists in a dianion form and that, on average, two of the four water molecules are protonated. The enhanced temperature dependence of the thermal parameters of the oxygen atoms of the water molecules suggested dynamic disorder of the water molecules. The solid-state magic angle spinning deuterium NMR spectrum of BSQB*4D2O revealed that deuterons are exchanged between heavy water molecules and oxonium ions with an exchange rate of ca. 700 Hz around 250 K and that deuterons start to migrate in a hydrogen-bonded cluster of water molecules. Ac dielectric measurements were also used to examine the dynamic process in the hydrated crystal. The dielectric permittivity of the crystal dramatically increased above 250 K with a distinct frequency dependence (epsilon' = 4.7 x 10(4) at 340 K and 1 kHz). The frequency dependence of tan delta at 290 K exhibited a maximum at 3.0 kHz, and this maximum shifted to lower frequencies when the temperature of the crystal decreased. These experimental results suggested that in the one-dimensional hydrogen-bonded chain of BSQB*4H2O a proton relay between oxonium ions and water molecules occurred within a cluster of four water molecules and that the relay was transmitted to the adjacent cluster mediated by the modulation of the negative charge distribution of the BSQB dianion. These phenomena were interpreted as the solitonic migration of the charged domain boundaries along the one-dimensional hydrogen-bonded chain. 相似文献
94.
Thin-layer chromatographic behavior of rare earths on silica gel with aqueous alkaline earth metal nitrate solutions as mobile phases 总被引:1,自引:0,他引:1
The TLC behavior of all the rare earths except Pm has been surveyed on silica gel (pH 7.0) pretreated with 0.1 mol L(-1) tris(hydroxymethyl)aminomethane and 0.1 mol L(-1) HCl with aqueous nitrate solutions of alkaline earth metals as mobile phases. The RF values of the lanthanides varied in a regular and characteristic way accompanied by the tetrad effect with increasing atomic number, and when the mobile phases were changed the RF values of each metal decreased in the order Mg2+ > Ca2+ > Sr2+ > Ba2+, as the crystal ionic radii of the alkaline earth metals increased. This adsorption sequence was not observed with alkali metal nitrate and alkali metal chloride mobile phases. A brief discussion concerning the effect on RF values of the solvent cations and the adsorption mechanism is included; also presented are typical chromatograms for the separation of multi-component mixtures containing adjacent lanthanides. 相似文献
95.
Dr. Yogesh Kumar Maurya Dr. Pingchun Wei Takahide Shimada Dr. Kazuhisa Yamasumi Dr. Shigeki Mori Prof. Dr. Ko Furukawa Dr. Hajime Kusaba Prof. Dr. Tatsumi Ishihara Prof. Dr. Yongshu Xie Dr. Masatoshi Ishida Prof. Dr. Hiroyuki Furuta 《化学:亚洲杂志》2021,16(7):743-747
A facile synthetic strategy towards conformationally stable chiral chromophores based on dimeric porphyrinoids has been established. A peculiar class of face-to-face intramolecularly interlocked corrole dimers were formed by the oxidative C−C coupling linked at the inner carbon sites upon simple treatment of copper(II) ions. Their intrinsic electronic structures were modulated by the peripheral corrole ring annulations, which lead to distinct optical properties and redox profiles. The stereogenic carbon centers implemented in the confused corrole skeleton provided a rationale for designing novel chiral materials. 相似文献
96.
Kunihisa Yoshida Yoshimasa Toyo-Oka Kazusada Takeda 《Journal of heterocyclic chemistry》1995,32(2):701-702
The electrooxidation of 1-methylpyrazole in methanol containing sodium cyanide produced 1-methyl-pyrazole-4-carbonitrile 2 and ?5-carbonitrile 3 in yields of 23 and 8%, respectively (2e-oxidation products), together with 4-methoxy-1-methylpyrazole-5-carbonitrile 4 (4e-oxidation product, 4%). 相似文献
97.
Kikuo Takeda Chikashi Akamatsu Yasuhiko Inoue 《Fresenius' Journal of Analytical Chemistry》1991,339(1):50-54
Summary Trace amounts of tin were concentrated by coprecipitation and determined by electrothermal atomisation atomic absorption spectrometry. Yttrium hydroxide coprecipitated quantitatively 0.1–3 g of tin from 50–500 ml of sample solution at pH 9.5–11.2. The atomic absorbance of tin increased about twice by using an impregnated graphite tube with yttrium. The impregnated graphite tube, furthermore, improved the reproducibility of the measurement of tin. A linear calibration graph was obtained in the range of 0.004–0.12 g/ml of tin. Twenty-three foreign ions did not interfere seriously. The method was applicable to the determination of tin in zinc metal. 相似文献
98.
A rapid, sensitive and selective high-performance liquid chromatographic method is described for simultaneous determination of eight sulfa drugs in meat and meat products using pre-column derivatization with fluorescamine. The drugs are sulfisomidine, sulfadiazine, sulfamerazine, sulfadimidine, sulfamonomethoxine, sulfamethoxazole, sulfadimethoxine and sulfaquinoxaline. The method includes blender extraction of 3-g samples with chloroform, partition with 3 M hydrochloric acid, derivatization with fluorescamine at pH 3.0 and subsequent high-performance liquid chromatographic analysis on a C18 column with fluorescence detection at an excitation wavelength of 405 nm and an emission wavelength of 495 nm. The drugs were separated with a mobile phase of acetonitrile-2% acetic acid (3:5) at 55 degrees C. The average recovery from samples fortified at 0.1 ng/g was 92.6% with a coefficient of variation of 6.2%. The detection limit was 0.01 ng/g for sulfaquinoxaline and 0.005 ng/g for the other seven drugs. The method was field-tested in a survey of 37 samples including beef (five), pork (seven), chicken (seven), ham (five), sausage (eight), bacon (two) and roast beef (three). Sulfadimidine was detected in one pork sample at the level of 0.295 ng/g and in ham at 0.178 ng/g. 相似文献
99.
Terauchi T Kamikawai T Vinogradov MG Starodubtseva EV Takeda M Kainosho M 《Organic letters》2011,13(1):161-163
A stereoarray isotope labeled (SAIL) lysine, (2S,3R,4R,5S,6R)-[3,4,5,6-(2)H(4);1,2,3,4,5,6-(13)C(6);2,6-(15)N(2)]lysine, was synthesized by the "head-to-tail" conversion of SAIL-Glu, (2S,3S,4R)-[3,4-(2)H(2);1,2,3,4,5-(13)C(5);2-(15)N]glutamic acid, with high stereospecificities for all five chiral centers. With the SAIL-Lys in hand, the unambiguous simultaneous stereospecific assignments were able to be established for each of the prochiral protons within the four methylene groups of the Lys side chains in proteins. 相似文献
100.
Novel neutral glycosphingolipids isolated from the plerocercoids of a tapeworm, Spirometra erinacei, may be expected to be involved in host-parasite interactions. We have synthesized this glycosphingolipid analogue containing 2-branched fatty alkyl residue in place of ceramide. Glycosylation of nonreducing-end trisaccharide derivative 15 with the reducing-end disaccharide derivative 17 in the presence of trimethylsilyl triflate (TMSOTf) gave the desired oligosaccharide derivative in good yield. The fully per-O-acylated 2-(trimethylsilyl)ethyl glycoside 19 was converted to glycosylimidate 20, which was condensed with 2-(tetradecyl)hexadecanol and subsequently deacylated to give the target glycosphingolipid analogue 22. 相似文献