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101.
Tatsuaki Yamaguchi Kimitoshi Saito Toshio Tsujimoto Hidetaka Yuki 《Journal of heterocyclic chemistry》1976,13(3):533-537
Nmr spectra of structural analogs of tenuazonic acid such as 3-acetyltetramic acid, 3-acetyltetronic acid, 3-acetylthiotetronic acid and others were investigated for elucidation of the tautomeric structures. These compounds have completely enolized β,β′-triketone systems, and the position of the nmr signals for the enolic proton shows that the strength of their intramolecular hydrogen-bonding is weaker than those of acyclic β,β′-triketones and six-membered cyclic triketones. The assignment was made for nmr signals split by the difference of the diamagnetic anisotropic effect in each tautomers. The percentages of each of the tautomers were calculated from the intensities of the corresponding nmr signals. The results were confirmed by means of 13C-nmr spectroscopy. 相似文献
102.
Kazuo Iguchi Soichiro Kaneta Kenichiro Mori Yasuji Yamada Atsushi Honda Yo Mori 《Tetrahedron letters》1985,26(47):5787-5790
New halogenated marine prostanoids, chlorovulone I, II and III were isolated from the stolonifer Quoy and Gaimard. The structure elucidation and the antitumor activity of chlorovulones were described. 相似文献
103.
Masahito Segi Katsuhiko Tanno Masumi Kojima Mitsunori Honda Tadashi Nakajima 《Tetrahedron letters》2007,48(13):2303-2306
1,3-Dipolar cycloaddition between aromatic selenoaldehydes, generated by thermal retro Diels-Alder reaction of anthracene cycloadducts, and nitrile oxides or nitrile imines proceeded efficiently to give the corresponding [3+2] cycloadducts as a single isomer in good yields, being 1,4,2-oxaselenazoles or 1,3,4-selenadiazoles, respectively. 相似文献
104.
Koji Yoshida Nobutaka Yamamoto Shinya Hosokawa Alfred Q.R. Baron Toshio Yamaguchi 《Chemical physics letters》2007,440(4-6):210-214
Inelastic X-ray scattering experiments have been performed on methanol as a function of density from ambient to the supercritical state. Positive dispersion of the sound velocity, as compared to the hydrodynamic values, is 50% in the ambient condition and decreases to zero at 0.50 g cm−3 over the momentum transfer Q = 1–10 nm−1 with lowering density; however, it increases again with a further decrease in density down to 0.20 g cm−3in the supercritical state only in the Q-range above 5 nm−1. These results have been interpreted as the formation of small oligomers in the low-density supercritical methanol. 相似文献
105.
Capillary zone electrophoresis was used for characterising nine samples of natural organic matter (NOM) using phosphate buffer (25 mM, pH 7) and various modifiers; methanol (50 mM), acetonitrile (10%,v/v), dimethyl sulfoxide (5%,v/v), and urea (5 M). Principal component analysis (PCA) was used to examine whether the electrophoretic profiles can be utilised as fingerprints for tracing the NOM samples to their source and/or type of location. It was found that all modifiers except methanol affect the electropherograms. Furthermore, it was found that the PCA analysis carried out on the electrophoretic profiles recorded in buffer solution modified by urea gave the best results for fingerprinting. The distribution of the fingerprints suggests a model for the humic substances in which all samples can be regarded as mixtures between two endmembers: autochtonous and allocthoneous NOM. 相似文献
106.
[reaction: see text] Phosphates from 3-substituted 4,4,4-trifluorobut-2-en-1-ols were found to be effective for construction of CF3-containing quaternary carbon centers by way of Cu(I)-catalyzed Grignard reactions in the presence of catalytic amounts of CuCN and trimethylsilyl chloride (TMSCl) in an anti S(N)2' manner. 相似文献
107.
Abstract— The title aminodioxetane prepared by photooxygenation of 2–(l-methyl-3-indolyl-3-phenyl-1,4-dioxene is fairly stable at ?46°C and gives on warming to room temperature an ultraviolet light at Λmax 320 nm, which corresponds to 377kJ/mol; the highest energy ever observed among the efficient chemiluminescent compounds. The efficiency of chemiluminescence and excited singlet molecule formation in n-hexane were 3.6% and at least 50%, respectively. Substitution and solvent effects suggest polar nature of the transition state as expected from the ‘CIEEL’ mechanism. In polar solvents, the dioxetane gives visible light (Λmax 400 nm in dichloromethane) as well as the UV light; the former being quenched by methanol. This is interpreted in terms of an intramolecular exciplex formation between the indole and phenyl groups. This is the first example of an intramolecular exciplex produced by the dioxetane decomposition. 相似文献
108.
Yuzuru Katagiri Kenzo Kanohta Kazuhiko Nagasawa Tadao Okusa Toshio Sakai Osamu Tsumura Yasuhiko Yotsui 《Analytica chimica acta》1981,133(4):535-543
A practical search system for proton n.m.r. spectra is reported. The coding rules and search algorithms are described in detail. Data for 8000 spectra have been converted into a computer-readable file from printed charts. Several search tests are used to evaluate the usefulness of the search system, and various effects of experimental conditions such as different instruments, frequencies and solvents on recall efficiency are described. The results presented indicate that the system should be applicable to routine analytical work. 相似文献
109.
110.
Biomimetic formation of gramicidin S by dimerization-cyclization of pentapeptide precursor on solid support 总被引:1,自引:0,他引:1
The biomimetic formation of gramicidin S, cyclo(-d-Phe-Pro-Val-Orn-Leu-)2, by the dimerization and cyclization of pentapeptide precursor without the protection of δ-amino group of the Orn residue was examined on a solid support. The cyclization of H-d-Phe-Pro-Val-Orn-Leu-oxime on a resin with an oxime group of 0.62 mmol/g in 1,4-dioxane directly gave gramicidin S in a 50% yield. The dimerization-cyclization mode on the solid support was similar to that of the biosynthesis of gramicidin S on an enzyme. 相似文献