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111.
A rapid radiochcmical procedure was developed for the separation of indium radionuclides from a mixed fission-product solution. An alcoholic pyridine solution is added to a uranium solution containing indium and tin carriers. The resulting tin precipitate is separated from the indium-containing solution by filtering through a cellulose membrane filter. The decontamination factor for tin is 2·103. Other fission products are only partially removed. The chemical yield of indium is about 44%, and the time required for the separation is about 10 sec. After the tin-separated indium has decayed, the tin daughters of indium are removed from all the other fission products at a specified time and measured, so that the amount of indium present at the time of the tin precipitation is determined. 相似文献
112.
Thevis M Opfermann G Schmickler H Schänzer W 《Journal of mass spectrometry : JMS》2001,36(9):998-1012
The steroid glucuronide conjugates of 16,16,17-d(3)-testosterone, epitestosterone, nandrolone (19-nortestosterone), 16,16,17-d(3)-nortestosterone, methyltestosterone, metenolone, mesterolone, 5alpha-androstane-3alpha,17beta-diol, 2,2,3,4,4-d(5)-5alpha-androstane-3alpha,17beta-diol, 19-nor-5alpha-androstane-3alpha,17beta-diol, 2,2,4,4-d(4)-19-nor-5alpha-androstane-3alpha,17beta-diol and 1alpha-methyl-5alpha-androstane-3alpha/beta,17beta-diol were synthesized by means of the Koenigs-Knorr reaction. Selective 3- or 17-O-conjugation of bis-hydroxylated steroids was performed either by glucuronidation of the corresponding steroid ketole and subsequent reduction of the keto group or via a four-step synthesis starting from a mono-hydroxylated steroid including (a) protection of the hydroxy group, (b) reduction of the keto group, (c) conjugation reaction and (d) removal of protecting groups. The mass spectra and fragmentation patterns of all glucuronide conjugates were compared with those of the commercially available testosterone glucuronide and their characterization was performed by gas chromatography/mass spectrometry and nuclear magnetic resonance spectroscopy. For mass spectrometry the substances were derivatized to methyl esters followed by trimethylsilylation of hydroxy groups and to pertrimethylsilylated products using labelled and unlabelled trimethylsilylating agents. The resulting electron ionization mass spectra obtained by GC/MS quadrupole and ion trap instruments, full scan and selected reaction monitoring experiments are discussed, common and individual fragment ions are described and their origins are proposed. 相似文献
113.
The reaction of the azomethine ylides 2a–c with cyclopropenones 3 and of 2a with methylene cyclopropenes 7 leads via (3+3)-cycloaddition to pyridones-4 5 and 1,4 - dihydro - N - methyl - 4 - methylene - pyridines 8, respectively. The merocyanine systems 8 exhibit marked solvatochromic and thermochromic properties. 相似文献
114.
Hydrocarbon oxidation vs C-C bond-forming approaches for efficient syntheses of oxygenated molecules
[Reaction: see text] A hydrocarbon oxidation approach has been applied to the construction of several linear (E)-allylic alcohols that have served as intermediates in the synthesis of natural products and natural product-like molecules. In the original syntheses, these intermediates were constructed using a standard Wittig-type olefination approach. We report here that routes to these same intermediates designed around a hydrocarbon oxidation approach are more efficient both in the total number of functional group manipulations (FGMs) and overall steps, as well as in the overall yield. 相似文献
115.
Barbara A. Bierl-Leonhardt Daniel S. Moreno Meyer Schwarz JoAn Fargerlund Jack R. Plimmer 《Tetrahedron letters》1981,22(5):389-392
The sex attractant pheromone of the citrus mealybug, (Risso), has been Identified as (1-)-(+)-2,2-dimethyl-3-(1-methylethenyl)cyclobutanemethanol acetate (VI). 相似文献
116.
Analytical procedures for quantification of peptides in pharmaceutical research by liquid chromatography–mass spectrometry 总被引:6,自引:0,他引:6
John H Walden M Schäfer S Genz S Forssmann WG 《Analytical and bioanalytical chemistry》2004,378(4):883-897
Peptide quantification by liquid chromatography–mass spectrometry (LC–MS) combines the high resolving power of reversed-phase (RP) chromatography with the excellent selectivity and sensitivity of mass spectrometric detection. On the basis of comprehensive practical experience in the analysis of small molecules, pharmaceutical research is developing technologies for analysis of a growing number of peptidic drug candidates. This article is a detailed review of procedures based on LC–MS techniques for quantitative determination of peptides. With the focus on pharmaceutical applications several technologies for sample preparation, various aspects of peptide chromatography, important characteristics of ESI–MS, selectivity of MS-detection modes, the large variability of internal standards, and modern instrumentation are discussed. The demand for reliable, robust, sensitive, and accurate methods is discussed using numerous examples from the literature, complemented by experiments and results from our laboratory. 相似文献
117.
Frédérique-Marie Rattis Josette Péguet-Navarro Pascal Courtellemont Gérard Redziniak Daniel Schmitt 《Photochemistry and photobiology》1995,62(5):914-916
Abstract— -Urocanic acid (UCA) represents the major ultraviolet B (UVB, 290–320 nm)-absorbing component of the skin. Trans-UCA is naturally produced in the stratum corneum and converts to the cis isomer upon UVB irradiation. In this study, we examined the effect of purified cis -UCA (about 99% of cis isomer) on the human Langerhans cell (LC) allostimulatory function by using the mixed epidermal cell-lymphocyte reaction (MELR). We found that addition of increasing amounts (6.5–400 μg/mL) of purified cis-UCA or (rara-UCA did not modify the T-cell response supported by enriched LC (eLC: 8–25% LC) as well as purified LC (pLC: 70–90% LC) suspensions. Because cis-UCA had no effect on the allostimulatory function of untreated LC, we investigated whether this compound could modify T-cell proliferation induced by UVB-irradiated LC. The UVB exposure of eLC or pLC to 100 J/m2 significantly inhibited the capacity of both suspensions to mount a T-cell response. However, addition of cis- UCA did not potentiate this UVB-induced immunosuppression. The eLC or pLC were then incubated with cis-UCA for 18 h at 37°C and washed before adding to allogeneic T cells. The obtained proliferative response was similar to that induced by control LC incubated in medium alone, demonstrating that pretreatment with cis -UCA did not alter human LC function. In conclusion, these results strongly suggest that cis-UCA has no direct effect on human LC antigen-presenting function. 相似文献
118.
Urocanic acid (UCA) is a chromophore in the stratum corneum. Ultraviolet radiation (ultraviolet B) has been shown to suppress mammalian cell-mediated immunity. The photoisomerization of trans -UCA to cis -UCA was proposed as the initiator of the suppression process. Cis -urocanic acid has been demonstrated to suppress immunity by a variety of experiments. Investigators should be aware that laboratory illumination may be capable of interconverting trans -UCA and cis -UCA during experimental manipulations. This possible inadvertent contamination of one isomer by the other may influence results. We demonstrated that fluorescent lamps, daylight, sunlight and incandescent lamps were able to bring about isomerization. Window glass and container materials of plastic and clear glass did not filter out effective wavelengths, but three commercial plastic diffusers on fluorescent fixtures prevented the isomerization. Because the molar extinction coefficient (ɛ) for cis -UCA is less than that of trans -UCA, we have exposed 0.1 m M trans -UCA to ambient light and monitored the change in absorbance. A method is given to calculate the percentage of trans and cis isomers from the absorbance at 277 nm when the initial purity and absorbance are known. Using this procedure, we validated the molar extinction coefficient of cis -UCA. 相似文献
119.
3-(Dimethylamino)-2,2-dimethyl-2H,-azirine as an α-Aminoisobutyric-Acid (Aib) Equivalent: Cyclic Depsipeptides via Direct Amid Cyclization In MeCN at room temperature, 3-(dimethylamino)-2,2-dimethyl-2H-azirine ( 1 ) and α-hydroxycarboxylic acids react to give diamides of type 8 (Scheme 3). Selective cleavage of the terminal N,N-dimethylcarboxamide group in MeCN/H2O leads to the corresponding carboxylic acids 13 (Scheme 4). In toluene/Ph SH , phenyl thioesters of type 11 are formed (see also Scheme 5). Starting with diamides 8 , the formation of morpholin-2,5- diones 10 has been achieved either by direct amide cyclization via intermediate 1,3-oxazol-5(4H)-ones 9 or via base-catalyzed cyclization of the phenyl thioesters 11 (Scheme 3). Reaction of carboxylic acids with 1 , followed by selective amide hydrolysis, has been used for the construction of peptides from α-hydroxy carboxylic acids and repetitive α-aminoisobutyric-acid (Aib) units (Scheme 4). Cyclization of 14a, 17a , and 20a with HCI in toluene at 100° gave the 9-, 12-, and 15-membered cyclic depsipeptides 15, 18 , and 21 , respectively. 相似文献
120.
Wolfgang Oppolzer Mark Kurth Daniel Reichlin Frank Moffatt 《Tetrahedron letters》1981,22(27):2545-2548
The chiral induction in the Diels-Alder addition → , assessed reliably by 19F-NMR-spectroscopy of the endo-esters , varied between 47 - 93% in favor of the 2-(R)-adducts depending on the auxiliary chiral group and the Lewis-acid catalyst. 相似文献