1,721,086 research outputs found
Kampf gegen Tropenkrankheiten und Förderung des wissenschaftlichen Nachwuchses im Kongo: Kristallisationspunkt Naturstoffchemie
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Selective treatment of cancer: Synthesis, biological evaluation and structural elucidation of novel analogues of the antibiotic CC-1065 and the duocarmycins
No full textNovel diastereomerically pure beta-D-galactosidic prodrugs (+)-12a-e of the cytotoxic antibiotics CC-1065 and the duocarmycins were prepared for an antibody directed enzyme prodrug therapy (ADEPT) using 4 as a substrate via a radical cyclization to give rac-5 and rac-6 followed by a chromatographic resolution of the enantiomers of rac-5, glycosidation and linkage to the DNA-binding units 10a-e. These only slightly toxic compounds can be toxified enzymatically by an antibody-p-D-galactosidase conjugate at the surface of malignant cells to give the cytotoxic drugs, which then alkylate DNA. The new prodrugs were tested in in vitro cytotoxicity assays showing excellent QIC(50) values of 4800 and 4300 for (+)-12a and (+)-12b, respectively. The absolute configuration of precursor (+)-5 was determined by comparison of the experimental CD spectrum with the theoretically predicted CD spectra and by X-ray structure analysis
Phenalinolactones A–D, terpenoglycoside antibiotics from Streptomyces sp. Tü 6071
No full textFour new terpenoglycoside antibiotics, phenalinolactones A-D were isolated from Streptomyces sp. Tu 6071. The structures were elucidated on the basis of detailed NMR and MS analyses. Phenalinolactones combine a diterpenoid tricycle, a 2,3,6-trideoxysugar a pyrrole-carboxylic acid and an uncommonly oxidized unsaturated gamma-lactone in a unique manner. Phenalinolactones show an inhibitory activity against Gram-positive bacteria. The Journal of Antibiotics (2011) 64, 229-232; doi:10.1038/ja.2010.165; published online 22 December 201
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
ChemInform Abstract: (+)‐Flavipucine (I), the Missing Member of the Pyridione Epoxide Family of Fungal Antibiotics
No full textSiamese-Twin Porphyrin: A Pyrazole-Based Expanded Porphyrin of Persistent Helical Conformation
No full textThe 3+3-type synthesis of a pyrazole-based expanded porphyrin 22H(4), a hexaphyrin analogue named Siamese-twin porphyrin, and its homobimetallic diamagnetic nickel(II) and paramagnetic copper(II) complexes, 22Ni(2) and 22Cu(2), are described. The structure of the macrocycle composed of four pyrroles and two pyrazoles all linked by single carbon atoms, can be interpreted as two conjoined porphyrin-like subunits, with the two opposing pyrazoles acting as the fusion points. Variable-temperature 1D and 2D NMR spectroscopic analyses suggested a conformationally flexible structure for 22H(4). NMR and UV/Vis spectroscopic evidence as well as structural parameters proved the macrocycle to be non-aromatic, though each half of the molecule is fully conjugated. UV/Vis and NMR spectroscopic titrations of the free base macrocycle with acid showed it to be dibasic. In the complexes, each metal ion is coordinated in a square-planar fashion by a dianionic, porphyrin-like {N-4} binding pocket. The solid-state structures of the dication and both metal complexes were elucidated by single-crystal diffractometry. The conformations of the three structures are all similar to each other and strongly twisted, rendering the molecules chiral. The persistent helical twist in the protonated form of the free base and in both metal complexes permitted resolution of these enantiomeric helimers by HPLC on a chiral phase. The absolute stereostructures of 22H(6)(2+), 22Ni(2), and 22Cu(2) were assigned by a combination of experimental electronic circular dichroism (ECD) investigations and quantum-chemical ECD calculations. The synthesis of the first member of this long-sought class of expanded porphyrin-like macrocycles lays the foundation for the study of the interactions of the metal centers within their bimetallic complexes.Fonds der Chemischen Industrie; DAAD; NSF [CHE-0517782, 1058846
(+)-Flavipucine, the Missing Member of the Pyridione Epoxide Family of Fungal Antibiotics
No full textFrom the culture extracts of the endophytic fungus, Phoma sp., isolated from the plant Salsola oppositifolia, five secondary metabolites were isolated and characterized. On biomalt agar medium, the strain produced the known substances chrysophanol (1) and hypothemycin (2), while from liquid-surface fermentations on a glucose/maltose medium, 2,4-pyridione derivatives were obtained. Interestingly, one of the isolated compounds, flavipucine (3a), showed a positive [a]D; it, thus, was the enantiomer of the known, but configurationally as yet unassigned (-)-flavipucine (3b). By using quantum-chemical circular-dichroism calculations, the absolute configuration of 3a was established. Moreover, the dihydro analog 5 of flavipucine was isolated for the first time. The stereostructures were determined by extensive spectroscopic data analysis, quantum-chemical circular dichroism calculations, and X-ray analysis. With the two enantiomeric side-chain analogues of flavipucine, fruit rot toxin A (FRT-A) (6a) and the recently published sapinopyridione (6b), the family of four naturally occurring substituted 2,4-pyridiones has become complete. Compound 3a exhibits antifungal activity against Phytophthora in fastens and moderate inhibitory activity against gram-positive and gram-negative bacteria
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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