1,720,963 research outputs found
Azaprostaglandins. Synthesis and antiulcer activity of 11-deoxy-8-azaprostaglandin analogs
No full textI and II were prepd. from Me 2-formyl-5-oxo-1-pyrrolidineheptanoate. They had less antiulcer activity than was expected from consideration of their structure
Influence of complexation with cyclodextrins on photo-induced free radical production by the common sunscreen agents octyl-dimethylaminobenzoate and octyl-methoxycinnamate
No full textThe influence of complexation with hydroxypropyl-b-cyclodextrin (HP-b-CD) or b-cyclodextrin (b-CD) on the photo-induced production of free radicals by the sunscreen agents octyl-dimethylaminobenzoate (ODAB), oxybenzone (OB) and octyl-methocycinnamate (OMC) was investigated. The formation of radical species during irradiation was detected by spin trapping electron paramagnetic resonance spectroscopy. 2,2,6,6-tetramethylpiperidine-1-oxyl, nitroxide radical (TEMPO) and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) were used as spin traps. Following the 4h illumination with simulated sunlight, OB didi not generate radicals. On the other hand, photoexcitation of solutions containing ODAB or OMC produced a marked decrease (> 40%) of the TEMPO signal intensity, demonstrating the formation of carbon-centered radicals. In addition, the results obtained on irradiation of ODAB solutions containing DMPO as spin trap indicated the generation of oxygen-centred radicals. Complexation of ODAB with HP-b-CD and OMC with b-CD markedly inhibited (>64%) the formation of free radicals generated by the sunscreens on exposure to simulated sunlight. Therefore, inclusion of ODAB and OMC into the cyclodextrin cavities minimizes their photosensitizing potential
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
An efficient approach to chiral nonracemic trans- and cis-decalin scaffolds for drimane and labdane synthesis
No full textOptically active trans - and cis -ring junction decalinic intermediates, which represent useful precursors for the synthesis of more complex natural targets, have been conveniently prepared starting from the β-ketoester obtained by standard chemistry from β-ionone and dimethyl carbonate. The chiral auxiliary (−)-menthol, easily attached to the β-ketoester through DMAP-catalyzed transesterification, allowed a clean separation of the diastereomers obtained in the key electrocyclization step, which were further elaborated to chiral intermediates already taken to drimane and labdane sesquiterpenes
A formal total synthesis (±)-forskolin through [3+2] nitrile oxide cycloaddition chemistry
No full textA formal synthesis of (±)-forskolin 1 has been accomplished utilizing 1,3-dipolar nitrile oxide cycloaddition chemistry either for an alternative and convenient preparation of the key enedione starting building block 3 as well as for the introduction of the suitably functionalized carbon framework required for assembling the pyranone unit. The synthetic sequence constitues a new synthetic route to the natural target since the enone 29 has been previously converted to (±)forskolin
A New Approach to Kainoids through Tandem Michael Reaction Methodology: Application to the Enantioselective Synthesis of (+)- and (−)-α-Allokainic Acid and to the Formal Synthesis of (−)-α-Kainic Acid
No full textA convergent, one-pot construction of functionalized pyrrolidine ring systems has been developed. The method is based on a tandem Michael reaction initiated by an intermolecular conjugate addition of a nitrogen nucleophile to an electrophilic olefin followed by trapping of the generated enolate by a built-in α,β-unsaturated acceptor. After model studies verified the feasibility of the process and gave information about its stereochemical outcome, the strategy was successfully applied to kainoid synthesis. The construction of the basic pyrrolidine skeleton of all the members of the family requires coupling of a suitable electrophilic subunit with a common donor‒acceptor fragment containing the nitrogen nucleophile. Thus, the enantioselective synthesis of (+)-α-allokainic acid (2) and the formal synthesis of its C-4 epimer (-)-α-kainic acid (1), have been accomplished using methyl vinyl ketone and 2-nitro-3-methyl-1,3-butadiene, respectively, as electrophilic partners of (S)-4-(benzylami..
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
Formal Synthesis of (±)-Ambrox®
No full textThe immediate precursor of (±)-Ambrox®1 has been conveniently prepared in a seven-step sequence starting from the readily available methyl 2-oxo-5,5,8a-trimethyldecahydronaphthalene-1-carboxylate 2, in turn derived by stannic chloride-mediated cyclization of methyl 3-oxo-5-(2,6,6-trimethylcyclohexen-1-yl)pentanoate. © 1995 Elsevier Science Ltd
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