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排序方式: 共有116条查询结果,搜索用时 15 毫秒
1.
Nobuo IKEKAWA Yoshinori FUJIMOTO Masaji ISHIGURO 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2013,89(8):349-369
Natural sterols often occur as a heterogeneous mixture of homologs, which had disturbed the progress of steroid research. Development and application of GC methodology overcame this difficulty and enabled us to obtain detailed sterol profiles. Together, fine synthesis of stereo-defined isomers and homologs of steroids having oxygenated side chains allowed us to compare them with natural samples as well as to investigate structure-activity relationship. Advance of HPLC technology also facilitated the determination of the stereochemical structure of naturally occurring steroidal compounds, which were obtained only in minute amounts. This review highlights three topics out of our steroid research that have been performed mainly at Tokyo Institute of Technology around 1970–1990. These are sterol metabolism in insects focusing on the mechanism of the conversion of plant sterols to cholesterol and ecdysone biosynthesis, the synthesis and biochemical research of active forms of vitamin D3 derivatives, and the synthesis and microanalysis of plant hormone brassinosteroids. 相似文献
2.
We study the enzymatic degradation of xenobiotic polymers mathematically. As a mathematical model, we derive a linear second-order hyperbolic partial differential equation which governs the evolution of the weight distribution with respect to the molecular weight. Given an initial weight distribution and a final weight distribution, we formulate a problem to determine a degradation rate. We establish a necessary and sufficient condition for which the problem has a local solution. We also introduce a numerical technique based on our analysis, and present a numerical result that we obtained applying weight distributions before and after enzymatic degradation of polyvinyl alcohol. 相似文献
3.
Twenty one methyl 5-phenoxy-2-furancarboxylates prepared from the reaction of methyl 5-nitro-2-furan-carboxylate with phenoxides via displacement of the nitro group. In the reaction of potassium 2-nitrophen-oxide with methyl 5-nitro-2-furancarboxylate at 110°-120°, 2,2′-dinitrodiphenyl ether was obtained as a main product. 相似文献
4.
Hamao Umezawa Tomohisa Takita Yukio Sugiura Masami Otsuka Susumu Kobayashi Masaji Ohno 《Tetrahedron》1984,40(3):501-509
Biosynthetic intermediates and synthetic analogues of bleomycin (BLM) have been investigated for their metal binding, dioxygen activation, and DNA cleavage. Molecular O2 was activated by the Fe(II) complex of a synthetic model ligand. Nucleotide sequence specificities in DNA cleavage by the BLM-Fe(II) and deglyco-BLM-Fe(II) complexes were almost identical. It has been shown that (1) the β-aminoalanine-pyrimidine-β-hydroxyhistidine portion of BLM is essential for the metal binding and dioxygen activation and (2) the bithiazole moiety contributes to the specific binding to guanine base of DNA. 相似文献
5.
Kunitaka Muramatsu Masaji Shimazu Junzo Tanaka Shigeo Horiuchi 《Journal of solid state chemistry》1981,36(2):179-182
Complex bismuth oxides with layered structure are prepared with a series of compositions in the system Bi2CaNb2O9-NaNbO3. It is found by X-ray powder diffraction that each compound is composed of more than two phases, which are described by a formula Bi2CaNan?2NbnO3n+3, e.g., in the sample with the nominal composition Bi2CaNb2O9 · 8NaNbO3, the phases with n = 6 to 8 appear predominantly. These phases are closely intergrown to each other. Moreover, high-resolution electron microscopy reveals that microsyntactic intergrowth frequently occurs in the phases with n > 5. The occurrence of the latter intergrowth is explained in terms of the bond length obtained. 相似文献
6.
The influence of amino acids on the formation of hematite particles from a forced hydrolysis reaction of acidic FeCl3 solution was examined. The spherical particles were produced on the systems with L-phenylalanine (L-Phe), L-serine (L-Ser) and L-alanine (L-Ala), though L-glutamine (L-Gln) and L-glutamic acid (L-Glu) gave ellipsoidal hematite particles. This morphological change in hematite particles is consistent with the order of stability constant of amino acids against to Fe3+ ions (K). The hematite particles produced with L-Glu, L-Gln and L-Ser were highly porous because they are formed by aggregation of cluster particles. These particles exhibited microporous behavior by outgassing the particles below 200 degrees C while they changed to mesoporous after treating above 300 degrees C by elimination of amino acids molecules remained between the cluster particles within the hematite particles. The hematite particles strongly depended on the nature of amino acids such as alternation of solution pH and adsorption affinity to beta-FeOOH and/or polynuclear primary (PN) particles. The systems on L-Ala and L-Phe, showing very rapid phase transformation from beta-FeOOH to hematite, exhibited the Ostwald ripening. A rotational particle preparation procedure suggested that the morphology of hematite particle is governed by the mode and strength of amino acid adsorption onto beta-FeOOH and/or PN particles. 相似文献
7.
The titled [3]radialenes are the first, water-soluble hexaaryl[3]radialenes with considerably high electron affinity, their alkali metal reduction giving rise to anion-radicals and dianions stepwise as fairly stable species in degassed tetrahydrofuran. 相似文献
8.
The first total synthesis of (±)-2-isocyanopupukeanane, a sesquiterpenoid of marine origin, has been completed following a strategy in which a common intermediate serves both for this synthesis and that of an isomeric, naturally occurring allomone, 9-isocyanopupukeanane. 相似文献
9.
The parent bicyclo[6.2.0]decapentaene is synthesized for the first time by thermal ring opening of its valence isomer. Thermal dimerization of the compound is also described. 相似文献
10.