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241.
3-Epi-6,7-dideoxyxestobergsterol A (2), an analogue of xestobergsterol A, has been synthesized from dehydroepiandrosterone (3) in 15 steps. The key synthetic intermediate, 15beta,16alpha-dioxypregn-17(20)E-ene derivative 8, was prepared from the corresponding 15beta,16beta-epoxide 6 by treating with acetic acid and titanium tetraisopropoxide. The 23-oxo side chain was constructed stereoselectively by orthoester Claisen rearrangement of 8 followed by introduction of an isobutyl group. Basic treatment of the 15,23-diketone 12 followed by deprotection gave the title compound 2. 相似文献
242.
D. Mondieig M. A. Cuevas-Diarte Y. Haget 《Journal of Thermal Analysis and Calorimetry》1989,35(7):2491-2500
Combination of three techniques of thermal analysis (hot stage polarising microscope, DSC, Guinier-Lenne) enabled the determination of the polymorphic behaviour of tetra 1,2,4,5-X benzene (X=Cl, Br). Thermal, calorimetric and crystallographic characterizations have been carried out. This study puts forward an interesting problem: theβ phase (P21/a, stable at room temperature) of the tetra chlorobenzene has similar arrangement to the two solid piases P21/a of tetra bromobenzene. Which one of these two forms is actually isomorphic with tetra chlorobenzene. 相似文献
243.
J. F. Chemin J. Roturier B. Saboya G. Y. Petit 《Journal of Radioanalytical and Nuclear Chemistry》1972,12(2):221-232
The use of direct observation of nuclear reactions (p,p′γ) is discussed. The main characteristics of this method are presented
and applied to the case of the miroanalysis of Si, S and Zn in GaSb. 相似文献
244.
245.
246.
I. Sakurada Y. Ikada T. Kawahara 《Journal of polymer science. Part A, Polymer chemistry》1973,11(9):2329-2342
The graft copolymerizations of styrene onto poly(ethylene terephthalate) (PET) and nylon fibers were carried out by the mutual irradiation and preirradiation methods. True graft copolymers were isolated from the products by extraction and characterized by hydrolysis and osmometry. Among the swelling agents employed, methanol was most effective for increasing the extent of grafting onto PET. In both methods of the grafting, the molecular weight of polystyrene formed in the substrate matrix was higher than one million if no chain-transfer agent was added to the monomer solution. Similar to the case of radiation grafting onto poly(vinyl alcohol) and cellulose, the isolated graft copolymer carried only one branch per copolymer molecule in both cases. Of great interest is the particularly low extent of grafting in the case of PET–styrene. This should be attributed to the low sensitivity of PET to radiation. The grafting site on the mother polymer molecule is discussed on the basis of the solution behavior of the branch polymers separated from the backbone. 相似文献
247.
Spectrophotometric determination of procaine hydrochloride is described. The procaine hydrochloride reacts with p-dimethylaminobenzalhyde in glacial acetic acid to form an Schiff base which is a yellow compound, and its maximum absorption wavelength is at 455nm, 455=3.46×104. The absorbance for procaine hydrochloride from 0.2 to 15 μg ml−1 obeys Beer's law. The linear regression equation of the calibration graph is C=5.866A−0.02, with a linear regression correlative coefficient is 0.9994 and relative standard deviation (RSD) of 1.7%; the detection limit is 0.1 μg ml−1; recovery is from 92.0 to 110.0%. Effects of reaction medium, temperature, gentamycin, beneylpenicillin, kanamycin, streptomycin, foreign ions, and stand for time on the determination of procaine hydrochloride have been examined. The results obtained by this method agreed with those by the official method (dead-stop titration). This method is rapid and simple, and can be used for the determination of procaine hydrochloride in injection solution of procaine hydrochloride. 相似文献
248.
Gallic acid was separated from a n-butanol extract of the fruit of Cornus officinalis Sieb. et Zucc by high-speed countercurrent chromatography in two steps using two solvent systems composed of ethyl-acetate-ethanol n-butanol-water (5:1.8:6, v/v/v) and ethyl acetate-ethanol-water (5:0.5:6, v/v/v) successively. From 1 g of n-butanol extract the method produced 60 mg of gallic acid at a purity of 97%. 相似文献
249.
250.
Y Suzuki 《Journal of chromatography. A》1991,569(1-2):407-419
The electrophoretic approaches for detection of mutant proteins in inherited diseases are briefly reviewed and discussed. Mutation of a protein, known to be associated with a specific inherited disease, is detected by immunoblotting, immunoprecipitation or enzyme staining, combined with various electrophoretic techniques. Some instrumental and technological devices for two-dimensional electrophoresis have been reported for the screening of mutant proteins in diseases of currently unknown etiology. 相似文献