1,720,962 research outputs found
New biologically active rubiginones from Streptomyces sp.
No full textFour new polyketides, named rubiginone D-2 (2), 4-O-acetyl-rubiginone D-2 (3), rubiginone H (6) and rubiginone I (7) were isolated from the cultures of Streptomyces sp. (strain Go N1/5). Their structures were established by a detailed spectroscopic analysis. The absolute configuration of 3 was determined by derivatization with chiral acids (Helmchen's method). The rubiginones inhibit the growth of some Gram-positive bacteria and are cytostatically active against different tumor cell lines
Streptazones A, B-1, B-2, C, and D: New piperidine alkaloids from streptomycetes
No full textFive new piperidine alkaloids (1-5), named streptazones A, B-1, B-2, C, and D, were isolated from Streptomyces strains FORM5 and Al. Their structures were established on the basis of detailed MS and NMR analysis. Streptazone A (1) exhibited significant cytotoxic activity against selected human tumor cell lines
New biologically active rubiginones from Streptomyces sp.
No full textFour new polyketides, named rubiginone D-2 (2), 4-O-acetyl-rubiginone D-2 (3), rubiginone H (6) and rubiginone I (7) were isolated from the cultures of Streptomyces sp. (strain Go N1/5). Their structures were established by a detailed spectroscopic analysis. The absolute configuration of 3 was determined by derivatization with chiral acids (Helmchen's method). The rubiginones inhibit the growth of some Gram-positive bacteria and are cytostatically active against different tumor cell lines
Determination of the absolute configurations of gamma-rubromycin and related spiro compounds by quantum chemical CD calculations
No full textThe absolute configurations of the spiro compounds gamma- and beta-rubromycin (2 and 3), natural antibiotics derived from actinomycetes, have been elucidated as (S) by quantum chemical calculations of their chiroptical properties and comparisons with the respective experimental CD spectra. Surprisingly, their spiro centers show an absolute configuration opposite to that of heliquinomycin (1), the only related spiro compound for which the configuration has hitherto been assigned. By further quantum chemical CD calculations, we were likewise able to confirm the absolute stereostructure of heliquinomycin (1), previously assigned by X-ray structural and degradative studies, thus providing independent corroboration of our results for gamma- and beta-rubromycin (2 and 3). Accordingly, it has emerged that diverse actinomycetes can generate different acetal configurations
Determination of the absolute configurations of gamma-rubromycin and related spiro compounds by quantum chemical CD calculations
No full textThe absolute configurations of the spiro compounds gamma- and beta-rubromycin (2 and 3), natural antibiotics derived from actinomycetes, have been elucidated as (S) by quantum chemical calculations of their chiroptical properties and comparisons with the respective experimental CD spectra. Surprisingly, their spiro centers show an absolute configuration opposite to that of heliquinomycin (1), the only related spiro compound for which the configuration has hitherto been assigned. By further quantum chemical CD calculations, we were likewise able to confirm the absolute stereostructure of heliquinomycin (1), previously assigned by X-ray structural and degradative studies, thus providing independent corroboration of our results for gamma- and beta-rubromycin (2 and 3). Accordingly, it has emerged that diverse actinomycetes can generate different acetal configurations
Structural and biosynthetic investigations of the rubromycins
No full textThe structure of the known secondary metabolite beta-rubromycin was corrected, based on spectroscopic and chemical investigations, from o-quinone 1 to p-quinone 6. By feeding [U-(13)C3]malonic acid to the rubromycin-producing strain, Streptomyces sp. Al, the polyketide origin of the skeleton was verified, but the identity of the starter unit and the folding mechanism of the polyketide chain are still unclear. From the culture broth of the strain A1, in addition to 6, the co-metabolites gamma-rubromycin (3), delta-rubromycin (4) and 3'-hydroxy-beta-rubromycin (7) were isolated. Their structures were determined or confirmed by detailed spectroscopic analysis. The rubromycins inhibit HIV-1 reverse transcriptase (RT) and are cytostatically active against different tumor cell lines
New co-metabolites of the streptazolin pathway
No full textVariation of the culture conditions of Streptomyces sp. strain Al, which produces streptazolin (1), resulted in the isolation of four new co-metabolites: 5-O-(beta -D-xylopyranosyl)streptazolin (3), 9-hydroxystreptazolin (4), 13-hydroxystreptazolin (5), and streptenol E (6). Their structures were established by spectroscopic and chemical methods. The possible biosynthetic relationship between the streptazolins and the streptenols is discussed
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
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
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