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T-Muurolol Sesquiterpenes from the Marine Streptomyces sp M491 and Revision of the Configuration of Previously Reported Amorphanes
No full textTwo new sesquiterpenes, 15-hydroxy-T-muurolol (3d) and 11,15-dihydroxy-T-muurolol (3e), along with the plant cadinenes T-muurolol (3f) and 3 alpha-hydroxy-T-muurolol (3g), were isolated from the marine-derived Streptomyces sp. M491. Their absolute configuration was established via NMR spectroscopy and X-ray crystallography of 3-oxo-T-muurolol (3a), which was reisolated from this strain. In addition, the absolute configuration of further sesquiterpenes previously reported from this strain was revised. These products were tested for their cytotoxicity against 37 human tumor cell lines using the MTT method. Only 3d was cytotoxic against a range of human tumor cell lines with a mean IC(50) of 6.7 mu g/mL
Electrophile- and Lewis acid-induced nitrone formation and 1,3-dipolar cycloaddition reactions in the 13 alpha- and 13 beta-estrone series
No full textdelta-Alkenyl oximes of 13 alpha-estrone 3-methyl ether undergo intramolecular 1,3-dipolar cycloaddition reactions with BF(3)center dot OEt(2) as catalyst, furnishing isoxazolidines. The reactions of the 13 alpha- and 13 beta-estrone oximes with electrophiles lead to cyclic nitrones in high yields via attack of the oxime nitrogen on the intermediate halonium ions. In the intermolecular cycloadditions of 16-halomethyl nitrones to N-phenylmaleimide, single condensed aza-D-homo isoxazolidines are formed with high chemo- and stereoselectivity
Electrophile- and Lewis acid-induced nitrone formation and 1,3-dipolar cycloaddition reactions in the 13 alpha- and 13 beta-estrone series
No full textdelta-Alkenyl oximes of 13 alpha-estrone 3-methyl ether undergo intramolecular 1,3-dipolar cycloaddition reactions with BF(3)center dot OEt(2) as catalyst, furnishing isoxazolidines. The reactions of the 13 alpha- and 13 beta-estrone oximes with electrophiles lead to cyclic nitrones in high yields via attack of the oxime nitrogen on the intermediate halonium ions. In the intermolecular cycloadditions of 16-halomethyl nitrones to N-phenylmaleimide, single condensed aza-D-homo isoxazolidines are formed with high chemo- and stereoselectivity
Enantio‐ and Diastereoselective Synthesis of Duocarmycine‐Based Prodrugs for a Selective Treatment of Cancer by Epoxide Opening
No full textFor the enantio- und diastereoselective synthesis of the prodrug 2, the N-tert-butyloxycarbonyl-protected amine 7 was alkylated with the enantio-pure epoxide 14 to give the amide 10. A regio- and facial-selective metal-mediated cyclisation by using a cuprate led to 17 with an inversion of configuration at C10. Subsequent transformation of the hydroxy group in 17 by using the Appel procedure afforded (1S,10R)-9 with an unusual double inversion owing to neighbouring-group participation of the N-tert-butoxycarbonyl group. (IS,10R)-9 is the key intermediate in the synthesis of the prodrug 2, which has been developed for a selective treatment of cancer based on the antibody-directed enzyme prodrug therapy as an analogue of the natural antibiotic duocarmycine SA (1)
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Computer-aided structure analysis of an epimerized dehydroepiandrosterone derivative and its biological effect in a model of reactive gliosis
No full textThe naturally occurring steroid dehydroepiandrosterone (DHEA) is reported to reduce glial fibrillary acidic protein (GFAP) overexpression in a model of reactive gliosis due to its conversion to estradiol by the enzyme aromatase. In the present study we examined the biological effect of a new epimerized derivative of DHEA, 16 alpha-iodomethyl-13 alpha-dehydroepiandrosterone derivative (16 alpha-iodomethyl-13 alpha-DHEAd, 16 alpha-iodomethyl-13 alpha-androst-5-en-3 beta,17 beta-diol), using the same model system, and compared the 3D structure of this molecule with that of DHEA and two steroidal type aromatase inhibitors, formestane and exemestane. The synthetic compound. in contrast to the reported effect of DHEA, was able to reduce GFAP overexpression only if the enzyme aromatase was inhibited. Data obtained from Computational calculations fortified by X-ray crystallography revealed that contrary to the nearly planar sterane framework of DHEA, the synthetic derivative 16 alpha-iodomethyl-13 alpha-DHEAd has a bent sterane skeleton, resulting in a 3D structure that is similar to that of formestane or exemestane. Moreover, 16 alpha-iodomethyl-13 alpha-DHEAd resulted to be metabolically more stable than DHEA. The results suggest that epimerization of the sterane skeleton of DHEA inclines the plane of the D ring, leading to a significantly altered biological activity. The synthetic molecule has a DHEA-like effect on GFAP overexpression when the enzyme aromatase is inhibited and the naturally occurring DHEA is ineffective in this respect. On the other hand, based on their Structural similarity it can be hypothesized that 16 alpha-iodomethyl-13 alpha-DHEAd applied alone might have a biological effect similar to that of formestane or exemestane. (C) 2010 Elsevier Inc. All rights reserved
Cyclopropyl Building Blocks for Organic Synthesis. Part 109. Cyclopentenones from a Novel [4 + 1]Cocyclization of Methylenecyclopropanes with Fischer Carbenechromium Complexes.
No full textVariations on the Author
Get PDF“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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