1,720,968 research outputs found
Convergent high stereoselective preparation of the C12-C24 fragment of Macrolactin A.
No full textThe convergent synthesis of the C12-C24 fragment (lower part) of macrolactin A is described. The
adapted strategy allowed building up the lower moiety by the assembly of three key intermediates
via organometallic addition. One hydroxylic stereogenic center was introduced by the application
of chiral sulfoxides methodology on fragment C19-C24. The preparation of the versatile 1,3-anti
diol synthon C12-C16 was achieved via opening of chiral epoxide and subsequent oxidation to a
hydroxy ketone. Finally, reductive elimination of the appropriate allylic dibenzoate with Na/Hg
introduced directly the C16-C19 (E,E)-diene unit, in a highly efficient stereoselective fashion
Concise Total Synthesis of Permethylated Anigopreissin A, a New Benzofuryl Resveratrol Dimer
No full textGoing 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
A Concise and Efficient Stereoselective Synthesis of the C1-C11 Fragment of Macrolactin A
No full textA stereoselective synthesis of the C1–C11 fragment of
macrolactin A, using original approaches for the introduction of the Z,E-diene stereochemistry and the C-7 stereogenic center, is reported.
The adopted strategy has allowed us to build up the fragment by the assembly of three key intermediates via cross-metathesis, Still–Gennari, and Wittig olefinations. Opening of the commercially available chiral benzyl glycidol epoxide to the corresponding homoallylic alcohol introduced the C-7 chiral center. A cross-metathesis reaction was used to create the C5–C4 E double bond. The Still–Gennari reaction introduced the 2Z,4E-diene moiety and finally the Wittig reaction with a propargylic triphenylphosphorane introduced directly the 1,3-enyne unit in a highly efficient stereoselective fashion
Synthèse totale du myricanol par macrocyclisation biarylique
No full textLe myricanol est un diarylheptanoïde cyclique extrait du Myrica cerifera (1) qui possède un fort potentiel de réduction du niveau de protéine tau dans les cellules (effet anti Alzheimer).(2) Il est également capable d’inhiber la production de NO.(3) et possède des propriétés anti-inflammatoires et des effets anti-androgènique(4). De plus, Il a été montré récemment que le myricanol était un candidat clinique pour la prévention et le traitement du cancer du poumon.(5) Comme pour la plupart des composés cycliques, l’étape clef de la synthèse du myricanol est la macrocyclisation, qui dans le cas des diarylheptanoïdes représente un challenge très important. Les contraintes imposées par le système macrocyclique empêchent généralement la rotation autour de la liaison biarylique des cyclophanes conférant au myricanol deux centres stéréogènes.(6)
Notre approche rétrosynthétique est illustrée par le Schéma 1. Le myricanol 1 est obtenu à partir du dérivé seco 2 par l’intermédiaire d’une réaction de Suzuki-Miyaura domino(7) qui n’a jamais été réalisé sur ce type de précurseur. Le diarylhepanoide dihalogéné 2 peut être facilement obtenu par métathèse croisée entre les composés insaturés 3 et 4. L’alcool allylique 3 peut être préparé énantiomériquement pur par allylation énantiosélective(8), nous ouvrant l’accès à la synthèse totale du (+)-aR,11S-myricanol.
(1) Tene, M.; Wabo, H. K.; Kamnaing, P.; Tsopmo, A.; Tane, P.; Ayafor, J. F.; Sterner, O. Phytochemistry 2000, 54 (8), 975–978.
(2) Jones, J. R.; Lebar, M. D.; Jinwal, U. K.; Abisambra, J. F.; Koren, J.; Blair, L.; O’Leary, J. C.; Davey, Z.; Trotter, J.; Johnson, A. G.; Weeber, E.; Eckman, C. B.; Baker, B. J.; Dickey, C. A. J. Nat. Prod. 2011, 74 (1), 38–44.
(3) Tao, J.; Morikawa, T.; Toguchida, I.; Ando, S.; Matsuda, H.; Yoshikawa, M. Bioorg. Med. Chem. 2002, 10 (12), 4005–4012.
(4) Matsuda, H.; Yamazaki, M.; Matsuo, K.; Asanuma, Y.; Kubo, M. Biol. Pharm. Bull. 2001, 24 (3), 259–263.
(5) Dai, G.; Tong, Y.; Chen, X.; Ren, Z.; Ying, X.; Yang, F.; Chai, K. Int. J. Mol. Sci. 2015, 16 (2), 2717–2731.
(6) Gulder, T.; Baran, P. Nat. Prod. Rep. 2012, 29 (8), 899–934.
(7) Ogura, T.; Usuki, T. Tetrahedron 2013, 69 (13), 2807–2815.
(8) Roush, W. R.; Hoong, L. K.; Palmer, M. A. J.; Park, J. C. J. Org. Chem, 1990, 55, 4109–4117
Approccio alla sintesi totale della Macrolattina A; potente inibitore del virus dell’HIV
No full textA General Protocol for the Regio High Yielding Opening of Different Glycidol Derivatives
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
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