1,720,968 research outputs found
Benzo-fused nitroheterocycles via benzannulation with nitro-1,3-butadienes: synthesis and application.
No full textNitroindoles, despite their scanty occurrence in nature, are attractive reactive intermediates in organic synthesis thanks to the coupling of the properties of the nitro group and of the indole moiety.[1] While nitration of the pyrrole nucleus can be easily achieved, nitration on the benzene ring represents a more challenging target. Ex-novo construction of the pyrrole onto a functionalized benzene derivative is, by far, the synthetic strategy most frequently exploited to access indole nitrated on the benzene ring. Herein, we expand the synthetic access to such nitroindoles reporting an original protocol based on the ex-novo construction of the benzene ring onto pyrrole employing mono- or dinitro-1,3-butadienes as powerful C4 benzannulating agents. This appealing, metal-free process characterized by high atom economy and mild reaction conditions allows to synthesize nitroindoles characterized by patterns of substitution not easy to be obtained otherwise.[2] Such unusual substitution patterns have demonstrated to be promising for further elaborations, i.e. the application of the classic Cadogan reaction conditions in order to access pyrrolocarbazoles with a rarely reported ring fusion.[3]
A very interesting side project regarded the synthesis of a series of atropisomeric naphthyl nitroindoles with two stereogenic axes originated from steric hindrances forcing the naphthyl groups out of the indole plane; the asymmetry of the indole “spacer” makes both the syn and anti diastereoisomers entail an atropisomeric pair. A stereodynamic analysis of such new atropisomeric nitroindoles has been done resolving atropisomers by chiral HPLC and determining their absolute configuration and the rotational barriers of the indole–naphthyl axes.[4]
This work, within an Erasmus+ project, demonstrates also the photochemical activity of electron donor-acceptor (EDA) complexes providing a way to generate radicals under mild conditions. This strategy has recently found application in chemical synthesis. Reported methods classically relied on the formation of intermolecular EDA complexes. Herein, we further expand the synthetic utility of this strategy demonstrating that indole-tethered ynones form an intramolecular electron donor-acceptor complex that can undergo visible-light-induced charge transfer to promote thiyl radical generation from thiols.[5] This initiates a novel radical chain sequence, based on dearomatizing spirocyclization with concomitant C–S bond formation. Sulfur-containing spirocycles are formed in high yields using this simple and mild synthetic protocol, in which neither transition metal catalysts nor photocatalysts are required. The proposed mechanism is supported by various mechanistic studies, and the unusual radical initiation mode represents only the second report of the use of an intramolecular electron donor-acceptor complex in synthesis.
[1] G. W. Gribble, in Prog. Heterocycl. Chem., Vol. 31, Elsevier, 2020, pp. 83-117.
[2] A. Pagano, M. Mancinelli, L. Bianchi, G. Giorgi, M. Maccagno, G. Petrillo, C. Tavani, Tetrahedron 2019, 75, 4506-4515.
[3] A. Benzi, L. Bianchi, M. Maccagno, A. Pagano, G. Petrillo, C. Tavani, Molecules 2019, 24, 3802.
[4] A. Pagano, E. Marotta, A. Mazzanti, G. Petrillo, C. Tavani, M. Mancinelli, Synlett 2018, 29, 2161-2166.
[5] H. E. Ho, A. Pagano, J. A. Rossi-Ashton, J. R. Donald, R. G. Epton, M. J. James, P. O'Brien, R. J. K. Taylor, W. P. Unsworth., Chem. Sci. 2020, DOI: 10.1039/c9sc05311e
New insights into oocyte cytoplasmic lattice-associated proteins
No full textOocyte maturation and preimplantati on embryo development are critical to successful pregnancy outcomes and the correct establishment and maintenance of genomic imprinting. Thanks to novel technologies and omics studies in human patients and mouse models, the importance of the proteins associated with the cytoplasmic lattices (CPLs), highly abundant structures found in the cytoplasm of mammalian oocytes and preimplantation embryos, in the maternal to zygotic transition is becoming increasingly evident. This review highlights the recent discoveries on the role of these proteins in protein storage and other oocyte cytoplasmic processes, epigenetic reprogramming, and zygotic genome activation (ZGA). A better comprehension of these events may significantly improve clinical diagnosis and pave the way for targeted interventions aiming to correct or mitigate female fertility issues and genomic imprinting disorders
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
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