1,720,963 research outputs found
Application of organocatalysis to the synthesis of pharmacological relevant scaffolds: chiral \u3b2-fluoroamines and aziridines. Total synthesis of carpanone, polemannone b & c and brevisamide, and a general approach for the construction of azabicyclic ring-containing alkaloids
Full text linkApplication of organocatalysis to the synthesis of pharmacological relevant scaffolds: chiral β-fluoroamines and aziridines. Total synthesis of carpanone, polemannone b & c and brevisamide, and a general approach for the construction of azabicyclic ring-containing alkaloids
No full textIn the field of organocatalysis, the use of small organic molecules has had a significant impact on chemical synthesis, providing a mild and practical alternative to the more conventional metal based catalyst. The selective introduction of fluorine in organic molecules has been shown to enhance binding interactions, improve metabolic stability, increase CNS penetrability and eliminate ancillary ion channel activity by attenuating amine basicity (pKa). On this basis, we have developed a rapid, general route to enantiopure β-fluoroamines (65-82% yield, 94-98% ee) and β,β-difluoroamines (64-78% yield) employing organocatalysis in both a two and one-pot procedure as relevant therapeutic scaffolds. Based on the extension of enantioselective α- fluorination of aldehydes to enantiopure β-fluoroamines, a simple, direct, one-pot organocatalytic approach to the formation of optically active non-activated aziridines will be presented. The approach is based on enantioselective α-chlorination of aldehydes, followed by reductive amination with readily available amines and subsequent base induced cyclization to afford chiral aziridines.
A catalytic CuCl2/(-)-sparteine oxidative β,β-phenolic coupling/tandem inverse-electron demand Diels-Alder reaction cascade of styrenyl phenols to give highly oxygenated benzoxanthanone natural product polemannones B & C, carpanone, and related unnatural congeners was achieved. The total synthesis of brevisamide, a marine cyclic ether alkaloid from Karenia brevis, was completed. This streamlined synthesis proceeds in 21 steps, in 5.2% overall yield and features a key SmI2 reductive cyclization step to access the tetrasubstituted pyran core.
The azabicyclic ring skeleton is an important structural subunit present in numerous biologically active alkaloid natural products and pharmaceutically significant compounds. Notable examples are pyrrolidine, quinolizidine, indolizidine, azocine and azepine (such as stemona alkaloids) alkaloids. A novel approach for the construction of highly diastereoselective azabicyclic compounds has been developed. The methodology is been applied towards the total synthesis of indolizidine and azepine alkaloids (stemaphylline and grandisine A & D)
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
What Comes Next? Simple Practices to Improve Diversity in Science
Full text linkRelative to our occurrence in the American workforce, black and brown scientists are underrepresented in science, technology, engineering, and math (STEM) fields. Though not insulated from cynics, there generally appears to be manifold support among the chemistry community to ensure underrepresented groups have equal participation in the field. This is clear given the emergence of support statements from several high-profile faculty members, many of whom are editors and board members of the fields' most important journals. What's lacking, however, are tractable action plans that can eliminate structural prejudice in science. In today's climate, a passionate plea against inequity (often delivered through social media or other powerful platforms) will rightfully and undoubtedly attract viewership. However, as the civil rights activists of the 1950s and 1960s would say, What happens after the message is delivered? In this editorial, we highlight examples of bias in science. Based on our experiences (chemists from industry, a historically black college and university (HBCU), and both private and public R1 universities), we offer solutions that will ensure scientists from underrepresented groups gain and maintain equal participation in science
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