1,720,987 research outputs found
Asymmetric synthesis of threo-(2S,3R)-2-amino-3-hydroxypentanedioic acid 5-amide (threo-gamma-hydroxyl-L-glutamine)
No full textEnantioselective Synthesis of (-)-(R)-5-hydroxy-1-(4-hydroxy-3-methoxyphenyl)3-decanone [(-)-(R)-(6)-gingerol]
No full textLEWIS ACID PROMOTED ALDOL ADDITIONS OF ALPHA-THIOSILYLKETENE ACETALS TO ALPHA-ALKOXY ALDEHYDES - DIASTEREOSELECTIVE SYNTHESIS OF SYN-ALPHA-METHYLENE-BETA-HYDROXY-GAMMA-ALKOXY ESTERS
No full textMgBr2 mediated addition of Methyl α-methylthio propionate silylketene acetal to α and α,β-alkoxy aldehydes is highly 3,4 -selective (18:1). -α- methylene-β- hydroxy-∂-alkoxy esters (6) and (8) are synthesized
ASYMMETRIC-SYNTHESIS OF 3,4-CIS-SUBSTITUTED BETA-LACTAMS VIA CHIRAL NOREPHEDRINE-DERIVED OXAZOLIDINES
No full textA diastereo- and enantioselective approach to functionalized 3,4-cis-β-lactams 9 and 16 was developed based on the use of chiral norephedrine-derived oxazolidines. The key-steps in the synthesis of 9 (Scheme 1) are the potassium hypochlorite epoxidation of aldehyde 1 and the lithium dimethylcuprate addition to acid 2, both steps proceed regio- and stereoselectively (98%) and in high yield. Standard synthetic methods and the Miller hydroxamate procedure for NC cyclization were used to complete the synthesis of the target cis-β-lactwn 9 (98% enantiomeric excess). In the synthesis of cis-substituted 3-amino-2-azetidinone 16 (Scheme 4) the key-step is the aqueous ammonia opening of epoxy acid 2 which proceeds regio- and stereoselectively (98%). The Miller-type cyclization of hydroxamate 15a under Mitsunobu conditions failed to give 16a in a yield higher than 35%
TITANIUM TETRACHLORIDE-MEDIATED ENANTIOSELECTIVE SYNTHESIS OF TRANS BETA-LACTONES
No full textPharmacologically interesting trans beta-lactones 11 and 16 were synthesized using a titanium tetrachloride-mediated enantioselective aldol reaction as the key synthetic step (see Scheme 2)
Stereoselective Synthesis of t -Butyl 2-Amino-2,5-dideoxy-L-lyxo-pentanoate: Formal Synthesis of L-Daunosamine
No full textEnantiomerically pure t-Butyl 2-amino-2,5-dideoxy---pentanoate 4c is synthesized via the highly diastereoselective MgBr2 mediated addition of dibenzylamino acetate silylketene acetal 2 to O-benzyl lactic aldehyde 3. The synthesis of γ-lactone 5c, a known intermediate in the synthesis of L-daunosamine and L-vancosamine, is also described
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
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