1,720,981 research outputs found
Photocatalyzed site- and stereoselective functionalization of β-fucosides
Full text linkThe modification of carbohydrates plays a crucial role in drug design and development. However, while functionalization at the anomeric position is widely explored, C-H bond activation still remains underdeveloped. In this context, photocatalysis allows access to traditionally hindered reactivity[1] and hydrogen atom transfer (HAT) reactions pave the way towards the direct editing of the sugar backbone.[2]
Here we present the photocatalyzed C-5 functionalization of β-fucosides. This is achieved using decatungstate anion (TBADT) as catalyst: the oxygen centers in its excited state are highly electrophilic[3] and, after deactivation of fucosides’ positions 1-4, they are able to generate an oxygen-stabilized tertiary nucleophilic radical in position 5.
A scope of several fucosides was carried out, with different yields according to the nature of the substituent at the anomeric position. The most promising substrates were treated with several vinylic olefins, achieving full regio- and stereoselectivity.
To the best of our knowledge, this work represents the first example of direct C-H functionalization at position 5 of monosaccharides.
References
1. D.J. Gorelik, S.P. Desai, S. Jdanova, J.A. Turner, M.S. Taylor, Chem Sci 2024, 15, 1204.
2. L. Capaldo, D. Ravelli, M. Fagnoni, Chem. Rev. 2022, 122, 1875.
3. V. De Waele, O. Poizat, M. Fagnoni, A. Bagno, D. Ravelli, ACS Catal. 2016, 6, 7174
Selectivity study in the functionalization of organic compounds promoted by radical and radical-like species
Full text linkOxidative C-H functionalization of organic substrates promoted by cheap, eco-friendly, and selective systems has received a great attention in recent years, since it allows to convert relatively unreactive bonds, ubiquitous in organic molecules, into functional groups suitable for further transformations. Oxidation of sulfides to sulfoxides is another important process due to the presence of sulfinyl functional group in many natural products and biologically active compounds, like anti-inflammatory or antibiotic drugs. Moreover, sulfoxides are important reagents in organic synthesis: in fact, chiral sulfoxides have been used as auxiliaries in asymmetric synthesis. In this thesis, the use of biomimetic nonheme iron complexes and N-hydroxyphthalimide (NHPI) as efficient and selective catalysts for the oxidation of alkylaromatic compounds, alcohols, and sulfides by hydrogen atom transfer (HAT) or S-oxidative processes has been described. Concerning the former systems, elucidation of mechanism and reactivity patterns of [(N4Py)FeII]2+ complex have been investigated in detail with respect to the generation of the iron-oxo and iron-peroxo active species both in common organic solvents and in non-common fluorinated solvents. For the N-hydroxyphthalimide catalyst, reactivity, and selectivity patterns of the corresponding N-oxyl radical (PINO) in S-oxidation from sulfur compounds have been analysed by kinetic and product studies.
In addition, the two systems can be used together in a mediated system, in which NHPI acts as efficient mediator in the oxidations of organic compounds promoted by the nonheme iron(IV)-oxo complex, enhancing its reactivity and expanding its oxidizing ability. In the mediated system, the increase of reactivity is associated to the oxidation of the mediator to the corresponding phthalimide-N-oxyl radical, which efficiently abstracts hydrogen atoms from the substrates regenerating the mediator NHPI. The possibility of a change of selectivity in the C-H functionalization of alkylaromatic compounds and alcohols has been studied in the presence of the NHPI mediator as a result of the different polar effects operating in the HAT processes promoted by [(N4Py)FeIV=O]2+ and PINO radical. Furthermore, a change of chemoselectivity in the competitive oxidation of sulfides, alkylaromatic compounds and alcohols by effect of variation of the oxidizing species in the absence or in the presence of the NHPI mediator has been investigated
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
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