1,720,961 research outputs found
Photocatalytic Vicinal Aminopyridylation of Methyl Ketones by a Double Umpolung Strategy
No full text© 2020 Wiley-VCH GmbHA photocatalytic double umpolung strategy for the vicinal aminopyridylation of ketones was developed using pyridinium N−N ylides. The inversion of the polarity of the pyridinium N−N ylides by single-electron oxidation successfully enables radical-mediated 1,3-dipolar cycloadditions with enolsilanes formed in situ from ketones, followed by homolytic cleavage of the N−N bond. Intriguingly, the nucleophilic amino and electrophilic pyridyl groups in the ylides can be installed at the nucleophilic α-position and electrophilic carbonyl carbon, respectively, which are typically inaccessible by their innate polarity-driven reactivity. This method accommodates a broad scope, and the utility was further demonstrated by the late-stage functionalization of complex biorelevant molecules. Moreover, the strategy can be successfully applied to enamides11sciescopu
Palladium(II)-Catalyzed Tandem Synthesis of Acenes Using Carboxylic Acids as Traceless Directing Groups
No full textA straightforward synthetic strategy for generating useful anthracene derivatives was developed involving palladium(II)-catalyzed tandem transformation with carboxylic acids as traceless directing groups. Carboxyl-directed C-H alkenylation, carboxyl-directed secondary C-H activation and rollover, intramolecular C-C bond formation, and decarboxylative aromatization are proposed as the key steps in the tandem reaction pathway. This novel synthetic route utilizes a broad range of substrates and provides a convenient synthetic tool that allows access to acenes
(c) 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim116151sciescopu
Visible-Light-Induced C–O Bond Formation for the Construction of Five- and Six-Membered Cyclic Ethers and Lactones
No full textVisible-light-induced
intramolecular C–O bond formation
was developed using 2,4,6-triphenylpyrylium tetrafluoroborate (TPT),
which allows the regiocontrolled construction of cyclic ethers and
lactones. The reaction is likely to proceed through the single-electron
oxidation of the phenyl group, followed by the formation of a benzylic
radical, thus preventing a competing 1,5-hydrogen abstraction pathway.
Detailed mechanistic studies suggest that molecular oxygen is used
to trap the radical intermediate to form benzyl alcohol, which undergoes
cyclization. This new approach serves as a powerful platform by providing
efficient access to valuable five- and six-membered cyclic ethers
and lactones with a unified protocol
Palladium-Catalyzed Divergent Arylation with Triazolopyridines: One-Pot Synthesis of 6-Aryl-2-alpha-styrylpyridines
No full textWe have developed a new strategy for palladium-catalyzed arylation reactions with triazolopyridines, wherein two different chemical transformations (C-3 vs. C-7) are observed by differentiating the substrates using different bases. The reactive palladium carbenoids were directly generated from triazolopyridines and underwent denitrogenative arylations with aryl bromides. Intriguingly, when potassium carbonate was replaced with potassium tert-butoxide, direct C-H arylation occurred at the most acidic position (C-7). Moreover, two different catalytic arylation events were successfully performed in a one-pot sequence, providing a convenient access to 6-aryl-2-alpha-styrylpyridines
(c) 2016 Wiley-VCH Verlag GmbH&Co. KGaA, Wein1661sciescopu
N-Heterocyclic carbene-catalyzed deaminative cross-coupling of aldehydes with Katritzky pyridinium salts
No full textThis journal is © The Royal Society of Chemistry.By employing an N-heterocyclic carbene (NHC) catalyst, we developed a versatile catalytic system that enables deaminative cross-coupling reactions of aldehydes with redox-active pyridinium salts. Katritzky pyridinium salts behave as single-electron oxidants capable of generating alkyl radicals enabled by the redox properties of the enolate form of Breslow intermediates. The resultant alkyl radical undergoes efficient recombination with the NHC-bound aldehyde-derived carbonyl carbon radical for the formation of a C-C bond. The mild and transition metal-free reaction conditions tolerate a broad range of functional groups, and its utility has been further demonstrated by the modification of a series of peptide feedstocks and application to the three-component dicarbofunctionalization of olefins11sciescopu
Identification of β-lapachone analogs as novel MALT1 inhibitors to treat an aggressive subtype of diffuse large B-cell lymphoma
No full textThe treatment of activated B cell-like DLBCL (ABC-DLBCL) is one of the urgent unmet medical needs because it is the most resistant DLBCL subtype to current therapies eagerly awaiting effective therapeutic strategies. Recently, the paracaspase MALT1 has emerged as a promising therapeutic target for the treatment of ABC-DLBCL. Herein, we report a new class of MALT1 inhibitors developed by high-throughput screening and structure-based drug design. The original hit, 4-amino-1,2-naphthoquinone series inhibited MALT1 activity but suffered from poor cellular activity. The extensive pharmacophore search led to the discovery of structurally similar β-lapachone that is a direct inhibitor of MALT1 and possesses favorable physicochemical properties. Molecular simulation studies suggested the possibility of the formation of a covalent bond between MALT1 and β-lapachone, which was corroborated by experimental wash-out studies. Inspired by this, we explored the structure-activity relationships by incorporating electron-withdrawing substituents at C8 position of β-lapachone. These MALT1 inhibitors exhibited potent antiproliferative activity to OCI-LY3 cell line and inhibited the cleavage of CYLD mediated MALT1. © 2015 American Chemical Society131111sciescopu
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
- …
