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11.
Shaginian A Rosen MC Binkowski BF Belshaw PJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(17):4334-4340
We describe the first solid-phase synthesis of dihydrovirginiamycin S(1), a member of the streptogramin B family of antibiotics, which are nonribosomal-peptide natural products produced by Streptomyces. These compounds, along with the synergistic group A components, are "last line of defense" antimicrobial agents for the treatment of life-threatening infections such as vancomycin-resistant enterococci. The synthesis features an on-resin cyclization and is designed to allow production of streptogramin B analogues with diversification at positions 1', 1, 2, 3, 4, and 6. Several synthetic challenges known to hinder the synthesis of this class of compounds were solved, including sensitivity to acids and bases, and epimerization and rearrangements, through the judicious choice of deprotection conditions, coupling conditions, and synthetic strategy. This work should enable a better understanding of structure-activity relationships in the streptogramin B compounds, possible identification of analogues that bypass known resistance mechanisms, and perhaps the identification of analogues with novel biological activities. 相似文献
12.
Toshimi Anzo 《Tetrahedron letters》2007,48(48):8442-8448
A formal synthesis of the antimicrobial tricyclic macrolides, tubelactomicins A and E, featured by a transannular Diels-Alder (TADA) approach, has been explored. The key issue for the transannular cyclization was the synthesis of a 24-membered macrolactone equipped with all the requisite functionalities, which has been achieved using an intramolecular Hiyama cross-coupling strategy. The Hiyama coupling reaction spontaneously triggered off the TADA reaction. From the endo-TADA adduct, formal syntheses of tubelactomicins A and E were achieved. The 24-membered macrolactone formation was also achieved via an intramolecular ring-closing metathesis approach. 相似文献
13.
Study on oxidation of polymers treated by high LET radiation 总被引:2,自引:0,他引:2
Wang Ruiyu Ha Hongfei Wang Yugang Zhao Weijiang Yan Sha Jin Changwen Wang Guanghui Wu Jilan 《Radiation Physics and Chemistry》1998,52(1-6):251-256
The oxidation of medical silicone rubber and segmented polyether urethane which were bombarded with 11.2 MeV Si+ or F+ at the dose of 5 × 1014 ions/cm2 was studied. In XPS measurements, it was found that the oxygen concentration on the surface of the implanted polymeric membranes had been increasing in three months at least. ESR measurement showed that some free radicals existed in these membranes and their quantities decreased with time. Chemical analysis proved that peroxides were generated in the γ irradiated membranes. The reason for the increasing of oxygen concentration was that free radicals combined with oxygen in the air and produced peroxides on the membrane surface. Moreover, in order to demonstrate the radiation mechanism, low LET (γ rays) radiation of such polymeric membranes was carried out for comparison 相似文献
14.
Shigeru Matsuo Tomoyoshi Murakami Ryuichi Takasawa 《Journal of polymer science. Part A, Polymer chemistry》1993,31(13):3439-3446
Crystalline poly(arylene ether nitrile) could be prepared by the polycondensation of 2,6-dihalobenzonitrile with resorcinol at 200°C in N-methylpyrrolidone in the presence of sodium carbonate. A reaction temperature of at least 200°C was necessary to attain high molecular weight polymer. Spectral data indicated that the polymer had the structure of a poly(meta-phenylene ether) with pendent nitrile groups on every other phenylene unit. Despite this structure, the crystallinity and the crystallization rate of the polymer were greater than those of the corresponding polymer with a para-linked structure. The glass transition temperature and the melting temperature of the polymer were almost the same as those of poly(etheretherketone) (PEEKTM). A series of other new poly(arylene ether nitriles) were also examined. The polymers derived from 4,4′-biphenol, dihydroxytetra-phenylmethane, dihydroxydiphenylsulfone, and 1,5-isoquinolinediol had high glass transition temperatures. The poly(arylene ether nitriles) exhibited excellent tensile strength compared with the corresponding ketone- or sulfone-containing polymers. Comparing the three different kinds of polymers containing the same bisphenol units, the order of glass transition temperature was found to be sulfone- > nitrile- > ketone-containing polymers, while the order of tensile strength was nitrile- > ketone- > sulfone-containing polymers. The excellent mechanical properties are attributable to dipole-dipole interactions of nitrile groups. © 1993 John Wiley & Sons, Inc. 相似文献
15.
Lämmerhofer M 《Journal of chromatography. A》2005,1068(1):31-57
A review on the advantages, peculiarities, and the potential of enantioselective capillary electrochromatography (CEC) in nonaqueous media is presented. Some fundamentals on CEC with particular focus on enantioselective CEC are discussed. The strategies, concepts, preferentially utilized chiral selectors and column technologies that have been utilized to succeed in highly efficient enantiomer separations by nonaqueous CEC are described thoroughly. 相似文献
16.
<正> 聚酯聚醚嵌段共聚物具有十分良好的物理和机械性能,能加工成橡胶、纤维、塑料胶粘剂等,近年来也有作为医用高分子材料的报道。所以对聚酯聚醚嵌段共聚物的研究十分活跃。然而,有关其光物理性质的研究还很少见。本文报道了混合聚醚-聚酯嵌段共聚物(MPEE)与反式1,4-二咔唑环丁烷(1,4-DCC)在激发态和基态下的相互络合作用。结果表明,MPEE可以猝灭1,4-DCC的荧光,同时形成激基复合物。在分散 相似文献
17.
18.
镧系与二甘醇-二-(邻羟基苯基)醚配合物的合成与表征 总被引:4,自引:0,他引:4
本文合成14种镧系高氯酸盐及硝酸盐分别与二甘醇-二-(邻羟基苯基)醚(记为EO_2(HOP)_2,EO=ethylene oxide,HOP为邻羟基苯基)形成的新配合物,确证组成为Ln(ClO_4)_3·EO_2(HOP)_2·nH_2O(Ln:La-Eu,n=10,Ln:Gd,Dy-Tm,Y,n=7),La_3(NO_3)_9·(EO_2(HOP)_2)_2·3H_2O及La(ClO_4)_2·EO_2H(OP)_25H_2O。文中研究了配合物红外,紫外、~1HNMR谱及~(13)C纵向弛豫时间T_1等,并讨论了共存阴离子、溶剂及配体不同端基对成配的影响。 相似文献
19.
In this work the potential of hydrophilic interaction chromatography (HILIC) is explored for the analysis of tetracycline antibiotics. The choice of the polar stationary phase is first discussed and it is demonstrated that aminopropyl stationary phases lead to higher efficiencies and peak symmetry than bare silica ones. The influence of the composition of the mobile phase is studied next : the concentration of the weaker solvent (acetonitrile), the nature and concentration of the more polar solvent (water or methanol), pH, the nature and ionic strength of the buffer. It is shown that high efficiencies are reached only with a citrate buffer that impairs the interactions with the residual silanol groups whatever the mobile phase pH is. We demonstrate that the citrate buffer strongly interacts with the cationic moiety of the aminopropyl stationary phase and thus reduces the accessibility of silanols. The separation of oxytetracycline, tetracycline and chlortetracycline is achieved in a few minutes at pH 3.5 or 5, with no peak tailing as usually observed in reversed phase liquid chromatography with an opposite elution order when compared with reversed phase liquid chromatography. 相似文献
20.
Osamu Sangen Singo Masuda Hidehiko Nakano Kazusige Yamana Kenichi Sasaki Naoki Ikeda 《Journal of polymer science. Part A, Polymer chemistry》1992,30(6):1171-1175
A new synthetic pathway of A–B–A tri-block copolyether which is composed of a hydrophilic poly(oxyethylene) unit as an A part and a hydrophobic poly(oxy-2-methyl-trimethylene) unit as a B part is proposed. Telechelic α-tosyl-ω-tosyloxypoly(oxy-2-methyl-trimethylene) derived from tosylation of poly(oxy-2-methyl-trimethylene glycol) (PMTG) was allowed to react with poly(ethylene glycol) (PEG) in the presence of sodium hydroxide. Tg of the resulting A–B–A tri-block copolyether (PEMG) (M?n = 1600) was ?72°C and its specific gravity [D415] was 1.055. 相似文献