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排序方式: 共有212条查询结果,搜索用时 31 毫秒
1.
Satoshi Ito Kazuya Koizumi Katsuhiko Fukuda Naohiro Kameta Tsukasa Ikeda Toru Oba Kazuhisa Hiratani 《Tetrahedron letters》2006,47(48):8563-8566
A new series of BINOL-based macrocycles with two phenolic protons have been synthesized via oxidative coupling reaction using CuCl(OH)-TMEDA. 相似文献
2.
3.
Makoto Oba 《Journal of organometallic chemistry》2006,691(6):1151-1153
A novel [2.2]metacyclophane in which two benzene rings are linked together with a carbon-carbon double bond and a disilane unit was prepared. Photolysis of the cyclophane in the presence of oxygen afforded the 4,5-dihydro-4,5-disilapyrene derivative via a transannular dehydrogenation reaction. 相似文献
4.
Onodera K Nakamura H Oba Y Ohizumi Y Ojika M 《Journal of the American Chemical Society》2005,127(29):10406-10411
Zooxanthellamide Cs (ZAD-Cs), C(128)H(220)N(2)O(53)S(2) (ca. 2.7 kDa), was obtained from a cultured marine dinoflagellate of the genus Symbiodinium as an inseparable isomeric mixture of polyhydroxylated 61- to 66-membered macrolides. The chemical structures of the components were clarified by detailed 2D NMR analysis to be the macrolactonized analogues of zooxanthellamide A (ZAD-A), which had been previously isolated from the same microalgae. Chemical lability of ZAD-Cs suggests that ZAD-A is an artifact derived from ZAD-Cs during the isolation steps. Three of the components possess the largest (63-, 64-, and 66-membered) ring sizes found to date among the natural macrolides. ZAD-Cs exhibited higher vasoconstrictive activity than that of the zooxanthellatoxins, the first vasoconstrictive macrolides from Symbiodinium sp. The structure-activity relationship suggests that the huge macrolactone structure is important for biological activity. The relationship between the structures of the polyol metabolites and the phylogenetic systematics of Symbiodinium sp. is also discussed. 相似文献
5.
Keishi Nishio Yuichi Watanabe Toshio Tsuchiya 《Journal of Sol-Gel Science and Technology》2003,26(1-3):245-250
In this study, we prepared Sr
x
Ba1 – x
Nb2O6 (x = 0.3, 0.5 and 0.7) thin film on 0.75 wt% La doped SrTiO3 (100) and (110) single crystal substrates. A homogeneous coating solution was prepared with Sr and Ba acetates and Nb(OEt)5 as raw materials, and acetic acid and diethlene glycol monomethyl ether as solvents. The substrates were coated with the solution by spin coating method. As-coated thin films were heated from 973 to 1273 K in air. The grains of the thin film on La doped SrTiO3 (100) were pillar shaped and arranged in right angle to each other. On the other hand, the grains of these thin films on La doped SrTiO3 were pillar shape and arranged in one direction. The crystallographic relationship of the thin film between Sr
x
Ba1 – x
Nb2O6 and substrate that the 130 and 310 direction of the thin film on the substrate were oriented with c-axis in parallel to the substrate surface. On the other hand, (hk0) phase diffractions of Sr
x
Ba1 – x
Nb2O6 thin film on the substrate (110) were investigated in the XRD theta-2theta measurement. It is expected that the Sr
x
Ba1 – x
Nb2O6 (x = 0.3, 0.5 and 0.7) were highly oriented or epitaxial growing on La doped SrTiO3 (110) single crystal substrate. 相似文献
6.
The quenching rate of singlet oxygen (1O2) by seven kinds of flavonoids (flavone, flavonol, chrysin, apigenin, rutin, quercetin, and myricetin) with 2,3-double bonds has been measured spectrophotometrically in ethanol at 35 degrees C. The overall rate constants kQ (= kq + kr, physical quenching + chemical reaction) increased as the number of OH groups substituted to the flavone skeleton (that is, the total electron-donating capacity of flavonoids) increases. The existence of catechol or pyrogallol structure in the B-ring is essential for the 1O2 quenching of flavonoids. Log kQ was found to correlate with their peak oxidation potentials, E(P); the flavonoids that have smaller E(P) values show higher reactivities. Similarly, log kQ values of flavonoids correlate with the energy level of the highest occupied molecular orbital (E(HOMO)), calculated by the PM3 MO method, and the longest wavelength pi pi* excitation energy (E(ex)). The contribution of the chemical reaction (kr) was found to be negligible in these flavonoids. The kQ values of rutin, quercetin, and myricetin [(1.21 approximately 5.12) x 10(8) M(-1) s(-1)] were found to be larger than those of lipids [(0.9 approximately 6.4) x 10(4) M(-1) s(-1)], amino acids (<3.7 x 10(7) M(-1) s(-1)), and DNA (5.1 x 10(5) M(-1) s(-1)). The result suggests that these flavonoids may contribute to the protection of oxidative damage in foods and plants, by quenching 1O2. 相似文献
7.
Hiroshi Hata Dr. Shigeru Yamaguchi Goro Mori Satomi Nakazono Taisuke Katoh Keishi Takatsu Satoru Hiroto Hiroshi Shinokubo Prof. Dr. Atsuhiro Osuka Prof. Dr. 《化学:亚洲杂志》2007,2(7):849-859
Highly regioselective and efficient borylation of a variety of porphyrins has been achieved by reaction with bis(pinacolato)diboron through C? H bond activation under iridium catalysis on the basis of the synthetic protocol developed by Miyaura, Hartwig, and Smith. A boryl group can be selectively introduced at sterically uncongested positions in the peripheral aryl groups of porphyrin substrates whose peripheral β‐positions are sterically hindered. Curiously, β substituents adjacent to the aryl group to be borylated have unexpectedly large effects on the regioselectivity, because the iridium catalyst can discriminate between subtle steric differences. Chemoselective borylation was also achieved for several functionalized porphyrins. This borylation protocol can be applied to various monomeric and oligomeric functional porphyrins, hence offering an efficient route to elaborate multiporphyrin‐based molecular constructs. 相似文献
8.
Abstract Bacteriochlorophyll d analogues that possessed a series of bulky substituents of OMe, OCOMe, and OCO t Bu at the C71-position were synthesized (Zn-complexes of methyl 71-substituted-3-(1-hydroxy-methyl)pyropheophorbide a). Aggregation behavior of these pigments was examined in comparison with a natural-type compound (C71-H) to elucidate the effects of size of the C71-moiety on self-assembly of the chlorins. These C71-substituted Zn-chlorins formed self-aggregates in 1% THF/hexane. The aggregates gave almost the same visible absorption bands, especially a ca. 2000-cm?1 red-shifted Qy peak; the spectra were essentially similar to those of the natural-type Zn-chlorin (C71-H). All the aggregates of the C71-substituted compounds showed similar exciton-type CD couplets in the red-shifted Qy region, which were different from the feature of the couplet of the C71-H Zn-chlorin aggregate. These spectral data suggested that the C71-moiety did not interrupt the intermolecular linkages between chlorin molecules but altered the supramolecular structure which influences the long-range chirality. 相似文献
9.
Analyse von Protease‐Inhibitor‐Interaktionen unter Nutzung evolvierbarer tricyclischer Microviridine
10.
Toni Neuwirth Dr. Anne-Catrin Letzel Cedric Tank Dr. Keishi Ishida Michael Cyrulies Dr. Lisa Schmölz Prof. Dr. Stefan Lorkowski Prof. Dr. Christian Hertweck 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(68):15855-15858
The anaerobe Clostridium acetobutylicum belongs to the most important industrially used bacteria. Whereas genome mining points to a high potential for secondary metabolism in C. acetobutylicum, the functions of most biosynthetic gene clusters are cryptic. We report that the addition of supra-physiological concentrations of cysteine triggered the formation of a novel natural product, clostrisulfone ( 1 ). Its structure was fully elucidated by NMR, MS and the chemical synthesis of a reference compound. Clostrisulfone is the first reported natural product with a diphenylsulfone scaffold. A biomimetic synthesis suggests that pentamethylchromanol-derived radicals capture sulfur dioxide to form 1 . In a cell-based assay using murine macrophages a biphasic and dose-dependent regulation of the LPS-induced release of nitric oxide was observed in the presence of 1 . 相似文献