1,720,958 research outputs found
Generating cis-aza-diaryl and triaryl ethers via organoBrønsted acid catalysed aza-Darzens chemistry
No full textWe report the efficient combination of SNAr and organic Brønsted acid catalysis protocols for the construction of cis-aziridine-derived biaryl and triaryl ethers. Using aza-Darzens chemistry mono-cis-aziridine-biaryl and bis-(cis-aziridine)-triaryl ethers have been generated; these motifs have significant potential as easily synthesised, functionalised precursors of a glycopeptide backbone.</p
“Dial Up and Lock In”: Asymmetric organo-Brønsted acid catalysis incorporating stable isotopes
No full textAn operationally simple organo-Brønsted-acid-catalyzed asymmetric and regioselective “dial up and lock in” of one or more stable isotopes into organic compounds is unknown. Here, we describe a newly designed, chemically versatile protocol mediating single- or multiple-isotope incorporation into aziridines via a one-pot, three-component, two-step process. By exploiting easy-to-generate isotope-derived starting materials, it allows complete control of isotope positioning, affords >95 atom % isotope incorporation, and generates cis-aziridines with excellent optical activities and regioselectivities. Demonstrating a “low entry point,” and thus easy access to a broad range of researchers, it requires no specialist laboratory equipment and employs readily attainable reaction conditions. Demonstrating their utility, the aziridines are easily transformed into sought-after chiral non-racemic α-amino acids appended with one to three (or more) identical or different isotopes. The widespread use of these compounds ensures that our methodology will be of interest to biological, medicinal, pharmaceutical, agrochemical, biotechnology, materials, and process chemists alike
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
Organocatalytic synthesis of chiral non-racemic aziridines, labelled with 2H, 15N, 13C stable isotopes
No full textAziridines are ‘keystone’ synthetic building blocks - relatively reactive, three-membered heterocycles with the potential for generating ‘secondary’ high value entities such as α- or β-amino acids via ring-opening reactions. Within this thesis, a one-pot asymmetric organocatalytic methodology is utilised for the synthesis of enantiomerically enriched cis-N-aryl-3-aryl-aziridine-2-carboxylates, labelled with stable isotopes: 2H, 13C and 15N. The reactions were catalysed by (S)-BINOL derived N-triflylphosphoramide Brønsted acid and stable isotopes were selectively introduced within an aziridine ring with > 95% isotopic enrichment. The desired compounds were generated in yields of up to 81% and up to 87% e.e. Furthermore optically active β-bromo-α-amino acid derivatives were generated via aziridine ring-opening methodology without loss of the isotopic label or e.e.
α-Arylglycinols are α-amino-β-alcohols, that can be found as structural motifs in synthetic and natural compounds or used as building blocks to access other functional groups. When oxidised, α-arylglycinols are converted to the α-arylglycines - a class of α-amino acids found in a wide range of bioactive compounds such as vancomycin and teicoplanin glycopeptide antibiotics. Successful incorporation of 2H or 13C stable isotopes at α- or β-positions of enantiomerically enriched N-Cbz protected α-arylglycinols is reported with > 95% isotopic enrichment, yields of up to 73% and up to 98% e.e.
Teicoplanin is a glycopeptide antibiotic, used against methicillin-resistant Staphylococcus aureus (MRSA), but the emerging bacterial resistance has escalated the search for new antibiotics. The synthesis of a non-labelled model fragment of the glycopeptide antibiotic teicoplanin is reported. The fragment is synthesised via an aziridination reaction and can be used as a template to generate teicoplanin analogues, both non-labelled and labelled with stable isotopes.
It is anticipated that the stable isotope incorporating methodologies described within this thesis will be applicable not only to the synthesis of novel glycopeptide antibiotics, but also to other biologically active compounds. The installation of stable isotopes affords compounds with highly valuable properties that can be used to study drug metabolism, toxicology, pharmacokinetics and reaction mechanisms
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
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