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91.
A derivative of L-vancosamine, a carbohydrate component of the antibiotics vancomycin and sporaviridin, has been prepared from L-lactic acid in a highly stereoselective manner. 相似文献
92.
Noritaka Ohtani Yukihiko Inoue Yasumasa Kaneko Shinsuke Okumura 《Journal of polymer science. Part A, Polymer chemistry》1995,33(14):2449-2454
The dilute solution viscosity was investigated for several polystyrene-based cationic io-nomers. It was found that intramolecular aggregation among the ionic groups was strongly dependent on the sizes of quaternary onium groups and counter anions. The extent of the aggregation was controled by the solvent polarity and the solvation to the ionic groups. When there was a strong selective soivation to small counter ions, the structure of onium groups shows a minor effect on the viscosity behavior, indicating little aggregation among the ionic groups. A strong solvation to small quaternary cations also eliminates the intra-molecular aggregation and the influence of counter ions was barely observable. When the selective solvation to counter ions was disabled by the enlarged size of the counter ions, however, the viscosity depended on onium group structure or spacer chain length. If the solvent solvates neither counter ions nor quaternary groups, the smaller the sizes of onium cation and counter anion, the lower the reduced viscosity due to an enhancement of the ionic aggregate formation. © 1995 John Wiley & Sons, Inc. 相似文献
93.
[reaction: see text] A Pd-catalyzed asymmetric allylic amination using aspartic acid derived P-chirogenic diaminophosphine oxides (DIAPHOXs) is described. Asymmetric allylic amination of both linear and cyclic substrates proceeded at room temperature to give the chiral allylic amines in 72-99% ee. 相似文献
94.
Three new prenylated butylphloroglucinol derivatives, takaneones A-C (1-3), were isolated from the MeOH extracts of the aerial parts of Hypericum sikokumontanum together with two new prenylated phloroglucinol derivatives, takaneols A and B (4 and 5). The structures of the isolated compounds were elucidated by exhaustive spectroscopic analysis. The cytotoxicities of the isolated compounds against human cancer cell lines were evaluated. Compounds 2-4 showed cytotoxicities against K562/Adr multi-drug resistant (MDR) cancer cells with IC50 values ranging from 4.7 to 10.0 μg/mL, which were slightly more potent than doxorubicin. Their potency of cytotoxicities against MDR cancer cell lines (KB-C2 and K562/Adr) were similar to those against sensitive cell lines (KB and K562). 相似文献
95.
A first synthesis of ascidiacyclamide, a cytotoxic cyclic peptide from ascidian, has been achieved through the cyclodimerization with diphenyl phosphorazidate(DPPA), which has unambiguously determined the absolute configuration of ascidiacyclamide as . 相似文献
96.
The enantioselective formal synthesis of (?)-aurantioclavine is described. The core tricyclic skeleton was synthesized using a Pd-catalyzed Heck insertion–allylic amination cascade. The stereocenter was constructed by a highly enantioselective organocatalytic asymmetric aziridination reaction. 相似文献
97.
The real structure of patellamide A, a cytotoxic lipophilic cyclic peptide from a marine tunicate, has been unambiguously determined by the synthesis of both its proposed and revised structures. 相似文献
98.
Tadashi Eguchi Yasumasa Dekishima Hideyuki Tamegai Norihiko Misawa Haruo Seto 《Tetrahedron》2005,61(8):2027-2035
Carotenoids are important natural pigments produced by various microorganisms and plants. Specific deuterium-labeling of these compounds is invaluable in biochemical and physiochemical research. In this paper, preparation of highly deuterated zeaxanthin, lycopene, and β-carotene using engineered Escherichia coli with fully deuterated mevalonate is described. Also described are physico-chemical properties of the obtained deuterated carotenoids. 相似文献
99.
Youngji Cho Jun-Seok Ha Mina Jung Hyun-Jae Lee Seunghwan Park Jinsub Park Katsushi Fujii Ryuichi Toba Samnyung Yi Gyung-Suk Kil Jiho Chang Takafumi Yao 《Journal of Crystal Growth》2010,312(10):1693-1696
The present study focused on the effect of an intermediate-temperature (IT; ∼900 °C) buffer layer on GaN films, grown on an AlN/sapphire template by hydride vapor phase epitaxy (HVPE). In this paper, the surface morphology, structural quality, residual strain, and luminescence properties are discussed in terms of the effect of the buffer layer. The GaN film with an IT-buffer revealed a relatively lower screw-dislocation density (3.29×107 cm−2) and a higher edge-dislocation density (8.157×109 cm−2) than the GaN film without an IT-buffer. Moreover, the IT-buffer reduced the residual strain and improved the luminescence. We found that the IT-buffer played an important role in the reduction of residual strain and screw-dislocation density in the overgrown layer through the generation of edge-type dislocations and the spontaneous treatment of the threading dislocation by interrupting the growth and increasing the temperature. 相似文献
100.