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1.
2.
Ferenc Sztaricskai Gyula Batta Zoltan Dinya Istvan F. Pelyvas Pal Herczegh Tamas E. Gunda Istvan Koczka 《Chemistry of Heterocyclic Compounds》1998,34(11):1296-1307
Starting from 3,5-dimethylisoxazole the carboxylic acids I and V, the amino acids VIII (L-) and IX (D-), and the ureido acids X (L-) and XI (D-) were prepared, which were used for the synthesis of the new cephalosporins XVIIb, XXa-c (L-), and XXIb (D-). Thein vitro antibacterial activity of these semi-synthetic antibiotics was studied. The resorption of XVIIb was investigated in mice.Research Group for Antibiotics of the Hungarian Academy of Sciences, H-4010 Debrecen, P.O. Box 70, Hungary. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1524–1535, November, 1998. 相似文献
3.
An efficient and concise approach to the synthesis of the macrolide core of the cryptophycins has been developed. A novel macrolactonization utilizing a reactive acyl-beta-lactam intermediate incorporates the beta-amino acid moiety within the 16-membered macrolide core. This modular approach, involving a cyanide-initiated acyl-beta-lactam ring opening followed by cyclization, was successfully applied to the total synthesis of cryptophycin-24. The strategy was also used in an efficient synthesis of the 6,6-dimethyl-substituted dechlorocryptophycin-52. In this case, the cyanide-initiated ring opening of the bis-substituted 2-azetidinone followed by macrolactonization was achieved through a catalytic process. 相似文献
4.
Pd-catalyzed coupling of the axially constrained, less reactive benzo[a]pyrene bay-region amino benzoates, derived from the tetrahydro and diol epoxides, with C-6 and C-2 halopurine deoxynucleosides offers an efficient approach to the synthesis of the corresponding nucleoside-epoxide adducts. Also reported are the first examples involving the coupling of a 6-chloropurine deoxynucleoside with these amines, a reaction that is difficult by direct halide displacement. Certain mechanistic aspects of this metal-catalyzed C-N bond formation are also discussed. [reaction--see text] 相似文献
5.
J. T. Hann 《Chromatographia》1987,24(1):510-512
Summary A quaternary mobile phase was optimized in conjunction with Fast LC techniques to separate α and β acids extracted from hops
in less than 4 minutes. The method is proposed for automated analysis of large numbers of hop samples and its usefulness is
demonstrated by comparing α-acid levels obtained by liquid chromatographic and conductometric techniques. Both assays provided
similar values for “fresh” hops but in “aged” hops liquid chromatography showed a lower level of α-acids. 相似文献
6.
Christina Haberhauer-Troyer Marizela Delic Brigitte Gasser Diethard Mattanovich Stephan Hann Gunda Koellensperger 《Analytical and bioanalytical chemistry》2013,405(6):2031-2039
A novel method for the simultaneous quantification of both glutathione (GSH) and its oxidized form glutathione disulfide (GSSG) by hydrophilic interaction chromatography–MS/MS has been developed and is critically discussed. Internal standardization based on isotopically labeled standards for both analytes is an absolute prerequisite for accurate quantification of this redox pair. Hence, a highly efficient and selective miniaturized procedure for the synthesis of isotopically labeled GSSG from commercially available glutathione-(glycine-13C2,15N) was established using H2O2 as oxidant and NaI as catalyst. Moreover, a tool is presented to monitor and hence uncover artifactual GSSG formation due to oxidation of GSH during sample preparation, which is the main source of systematic error in GSSG analysis. For this purpose, we propose to monitor the oxidation product formed by reaction of naturally occurring GSH with the isotopically labeled GSH used as internal standard. For the determination of GSH/GSSG ratios in yeast, different extraction methods based on (1) hot extraction with aqueous, acidic, or organic solvents, (2) mechanical cell lysis, and (3) extraction at subambient temperature were investigated in terms of recovery, extraction efficiency, and artifactual formation of GSSG. Total combined uncertainties of as low as 25–30 % (coverage factor?=?2) for the determination of GSH/GSSG ratios without derivatization were made possible by the addition of the internal standards early in the analytical procedure (before extraction) and immediate analysis of the analytes. 相似文献
7.
Dileep Kumar Kian-Eang Neo Malik Abdul Rub Ze Lene Tan Woan Lin Beh Hann Ling Wong 《Journal of Dispersion Science and Technology》2013,34(11):1657-1664
The present work is aimed at studying the interaction between copper-glycyltyrosine [(Cu(II)-Gly-Tyr)]+ and ninhydrin in water and in micelles formed by cetyltrimethylammonium bromide (CTAB) using spectrophometric measurements at 80°C and pH 5.0. The order of reaction remains the same in the two systems, that is, first- and fractional-order kinetics with respect to [Cu(II)-Gly-Tyr]+ and [ninhydrin], respectively, in the excess of ninhydrin over [Cu(II)-Gly-Tyr]+. It was observed that the product formed is same in both the media. The reaction is catalyzed by CTAB, and the maximum rate enhancement is about three fold. Quantitative kinetic analysis of kψ–[CTAB] data was explained in terms of pseudo-phase of the micelles (assuming the association/incorporation of both the reactants at the micellar surface). 相似文献
8.
An efficient synthesis of 13-epi-7-O-(triethylsilyl)baccatin III from 13-deoxybaccatin III is described. Oxidation of 13-deoxy-7-O-(triethylsilyl)baccatin III with tert-butyl peroxide, followed by reduction with SmI(2), produced 13-epi-7-O-(triethylsilyl)baccatin III in good overall yield. The preparation of 13-oxo-7-O-(triethylsilyl)baccatin III from 13-epi-7-O-(triethylsilyl)baccatin III using tetrapropylammonium perruthenate and N-methylmorpholine N-oxide is also reported. 相似文献
9.
Numerical modelling of the Gaussian beam diffraction by a wire near the Fraunhofer limit is presented. Two cases are considered: the case of the wire being on the axis of the beam and the case of the wire being off-axis. For the case where the wire is on the axis, the displacements of the diffracted minima are calculated. For the off-axis case, the changes in the positions of the maxima and minima and the power density are calculated. The conditions are determined at which the measurements made using a Gaussian beam can be calculated using the formula for plane waves. This work arises in connection with research being performed into the Doppler spectrum of big particles. 相似文献
10.
Certain anthracenophanes undergo photochemistry without light, sensitised by active oxalates. Although the quantum yield of sensitisation is extraordinarily high, no direct evidence for the expected radical cation intermediate has been found. 相似文献