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Efficient Lewis Acid Systems for the A3 Coupling reaction
No full textEfficient Lewis Acid Systems for the A3 Coupling reaction
Cimarelli C., a Navazio F.,a Rossi F. V.a, Del Bello F., Marcantoni E.a
aSchool of Science and Technology, Chemistry Division, University of Camerino, Via S. Agostino 1, 62032 Camerino; e-mail: [email protected]
Propargylamines are an attractive class of molecules because of their particular molecular skeleton, that contains an amine group located in β-position to an alkyne moiety suitable for many chemical transformations. In recent years they received a growing interest as key intermediates for several biologically active compound, natural products and also different heterocycles.[1,2]
Our goal was the development of green and simple methodologies for the synthesis of secondary propargylamines by Lewis acid catalyzed or promoted A3 reaction among aldehydes, alkynes and primary amines, that are in general less applied in such reactions because of their lower reactivity. In particular, we studied two different pathway: the CuSO4/NaI system in one pot fashion and the CeCl3/CuI system in one pot/two steps way (Scheme 1).
Scheme 1. CeCl3·7H2O/CuI and CuSO4/NaI catalyzed A3 reaction.
Heptahydrated CeCl3 is reported to be an excellent catalyst for many useful organic transformation as the synthesis of imines. Its efficacy as Lewis acid is enhanced in the presence of inorganic iodides/iodide salt and being cooper the transition metal of choice for A3 reactions, CuI was used.[3]
Also the CuSO4/NaI couple has revealed to be an interesting Lewis acid system as an alternative to CeCl3/CuI system which allow the formation of CuI in situ by quantitative spontaneous reaction that takes place in few seconds.[4]
Typically CuSO4/NaI catalysed reactions are faster than CeCl3·7H2O/CuI reactions, but suffer of some disadvantages, such as lower yields, and a narrower applicability. Both reaction conditions have been applied to different aldehydes (aromatic and aliphatic) and to chiral starting materials, the amine in general has no effect on the reaction outcome.
The relevant Glaser coupling drawback observed in the CuSO4/NaI system conditions has been suppressed by adding some benzoic acid, and has not been observed with the CeCl3/CuI system.
References:
1) Lauder, K.; Toscani, A.; Scalacci, N.; Castagnolo, D. Chem. Rev. 2017, 117, 14091.
2) Peshkov, V. A.; Pereshivko, O. P.; Van der Eycken, E. V. Chem. Soc. Rev. 2012, 41, 3790.
3) G. Bartoli, E. Marcantoni, M. Marcolini, L. Sambri, Chem. Rev. 2010, 110, 6104.
4) Bailey, A. D.; Cherney, S. M.; Anzalone, P. W.; Anderson, E. D.; Ernat, J. J.; Mohan, R. S. Synlett 2006, 215
The 2-substituted imidazoline ring linked to an aromatic moiety by a biatomic bridge: a bioversatile scaffold
Full text linkNo abstrac
Zinc coordination complexes as anticancer agents
No full textZinc, present in all forms of life, is an essential element for humans. It is one of the most abundant metals in our body. Because of its importance, any malfunctions of its homeostasis can lead to different disease states, also related to the development of cancer. On the other hand, several Zn complexes have been recognized for their biological activities principally for preventive effects on infectious diseases and for low toxicity. Among different applications in medicinal chemistry, zinc-based complexes have shown to be appealing as anticancer drugs with low toxicity or as photosensitizers in Photo Dynamic Therapy. Here we present an overview of Zn coordination complexes proposed in the last six years as anticancer agents, trying to find a correlation between their chemical features and biological activity, and to evidence the potential perspectives of their use. Despite the great amount of work done in this field, this is the first exhaustive review on antitumor zinc complexes, that might be of wide interest for the researchers in the design and synthesis of new antitumor zinc-based drugs alternative to platinum derivatives
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
DESIGN, SYNTHESIS AND BIOLOGICAL EVALUATION OF NOVEL POTENT MUSCARINIC RECEPTOR ANTAGONISTS BEARING THE 1,4-DIOXANE NUCLEUS
No full textThe muscarinic acetylcholine receptor (mAChR) family consists of five closely related members (M1-M5) with different molecular and signaling properties. mAChRs mediate several functions in the central nervous system, as well as in the periphery. The 1,4-dioxane ring has recently demonstrated to be a bioversatile scaffold for the development of compounds binding mAChRs. In particular, we have demonstrated that it is possible to obtain mAChR agonists or antagonists, depending on the nature of the substituent in position 6 of the 1,4-dioxane nucleus. Specifically, the presence of bulky substituents in position 6 allowed us to obtain potent antagonists, including the 6,6-diphenyl derivative 1. In addition to quaternary
ammonium compounds, such as 1, ligands bearing a tertiary amine (2) (Figure) also proved to act as antagonists at mAChRs, probably by binding in the cationic form.
In this study, we have designed and synthesized the quaternary ammonium compounds 3-5 and the tertiary amines 6-8 by inserting in position 2 of the potent 6,6-diphenyl-1,4-dioxane mAChR antagonists 1 and 2, respectively, substituents of
different steric bulk, with the aim of evaluating their role on the mAChR affinity. Moreover, considering the critical role of chirality in the mAChR affinity of 1,4-dioxanes, the enantiomers (+)-6 and (-)-6 were also prepared and studied. The most
interesting result was obtained with the 2-methyl derivative 6 and its enantiomers which, surprisingly, in binding studies exhibited a biphasic curve, showing two distinct pKi values for all the five mAChRs. Molecular modelling studies were
performed to rationalize this unexpected experimental observation
Temperature estimation of cooking vessel content via EKF and sliding mode observers in induction cooking systems
No full textVariations 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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