1,720,986 research outputs found
SEPARATION OF 18-ALPHA-GLYCYRRHETINIC AND 18-BETA-GLYCYRRHETINIC ACID BY HIGH-PERFORMANCE THIN-LAYER CHROMATOGRAPHIC DENSITOMETRY
No full textA high-performance thin-layer chromatographic method with scanning densitometry was developed for the simultaneous separation and determination of 18-alpha- and 18-beta-glycyrrhetinic acid
DETERMINATION OF THE REACTIVITY OF URACIL DERIVATIVES WITH RESPECT TO METHYL-IODIDE BY HIGH-PERFORMANCE THIN-LAYER CHROMATOGRAPHIC DENSITOMETRY
No full textA high-performance thin-layer chromatographic method is described for the investigation of the methylation rates of uracil, 5-fluoro-, 5-chloro-, 5-bromo-, 5-methyl- and 5-nitrouracil and their N1- and N3-methyl derivatives. The method allowed the amounts of compounds obtained, the time required to complete the reaction and therefore the reactivity of the uracil derivatives to be determined. The N1- and N3-methyl and N1,3-dimethyl derivatives were synthesized and separated by droplet countercurrent chromatography and/or medium-pressure liquid chromatography and their R(F) values were determined in different solvent systems by thin-layer chromatography
THE METHYLATION, OXIDATION AND CRYSTALLOGRAPHIC CHARACTERIZATION OF IMIDAZOLE DERIVATIVES
No full textCompounds 2, 3 and 4 were synthesized and the crystal and molecular structures of 1 and 4 were determined. An hptlc technique for studying the methylation rate of 1 and the oxidation rate of 2 was applied
Synthesis and aldose reductase inhibitory activity of benzoyl-amino acid derivatives
No full textA series of N-(4-methoxy, 4-fluoro, 4-trifluoromethyl and 4-nitrobenzoyl)-L-amino acids was synthesized and their inhibitory activity towards bovine lens aldose reductase (ALR2) was tested. (C) 1998 Elsevier Science S.A. AII rights reserved
Crystal and molecular structure of 18α-glycyrrhetinic acid
No full textThe crystal structure of 18-alpha-glycyrrhetinic acid (trans junction of the D/E rings) has been determined in order to compare its stereochemical features with those of the known 18-beta form (cis junction of the D/E rings). The two stereoisomers exhibit different physiological actions. A comparison of their common moieties shows significant differences between the conformations of the unsaturated C ring, with some torsion angles differing by more than ten degrees. Further differences involve the convexity of the ABCD region, which in the alpha-form is smaller than that observed in the beta-isomer, and smaller than that reported for the mean steroid configuration.The crystal structure of 18α-glycyrrhetinic acid (trans junction of the D/E rings) has been determined in order to compare its stereochemical features with those of the known 18β form (cis junction of the D/E rings). The two stereoisomers exhibit different physiological actions. A comparison of their common moieties shows significant differences between the conformations of the unsaturated C ring, with some torsion angles differing by more than ten degrees. Further differences involve the convexity of the ABCD region, which in the α form is smaller than that observed in the β isomer, and smaller than that reported for the mean steroid configuration
SYNTHESIS, CHARACTERIZATION, AND CRYSTALLOGRAPHIC ANALYSIS OF SOME BENZOIMIDAZOLE DERIVATIVES
No full textA number of benzenesulfonyl derivatives of benzoimidazol-2-ylamine and 1-methyl-benzoimidazol-2-ylamine were synthesized, their synthesis reactions under different experimental conditions being monitored by hptlc. The crystal and molecular structures of N-(1-benzenesulfonyl-1,3-dihydrobenzoimidazol-2-ylidene)benzenesulfonamide (4) and N-(1-benzenesulfonyl-3-methyl-1,3-dihydro-benzoimidazol-2-ylidene)-benzenesulfonamide (7) were determined by X-ray diffraction analysis. The structure of compound 4 is made up of two crystallographically independent molecules and that of compound 7 of one molecule. In both cases, the structure contains the imido form of the molecules. There are strong conjugative effects between the imido groups and the imidazolic rings. Weak intramolecular C-H ... O hydrogen bonding interactions could influence the molecular conformations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Synthesis, antimicrobial and genotoxic properties of some benzoimidazole derivatives
No full textA number of 1H-benzoimidazol-2-ylamine and of 1-methyl-1H-benzoimidazol-2-ylamine derivatives were synthesized and the crystal and molecular structure of N-[4-(2-amino-benzoimidazole-1-sulfonyl)-phenyl] acetamide was determined by X-ray diffraction analysis. The compounds obtained were investigated for antimicrobial and genotoxic activities
Synthesis, characterization, crystallographic analysis, antifungal and genotoxic properties of some 1-methyl-1H-imidazoles
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