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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Organokatalytische Synthesen biologisch aktiver Naturstoffe : Totalsynthesen von Amaminol A und B und (+)-Mitsugashiwalacton sowie Synthesen 2,6-disubstituierter Tetrahydropyranen
No full textAmaminol A and B are two diastereomeric 1,2-aminoalcohols of marine origin with a basic structure of a trans-fused bicyclononane. This work, for the first time, developed a complete synthesis of amaminol B, which, starting from 2E,4E-hepta-2,4-dien-1-ol and in a process of only eleven steps achieves a total yield of 21%. The overall concept of the complete synthesis of amaminol A and B is characterised by three key organocatalytic steps. The basic structure of amaminol A and B including the desired configuration of the four stereocenters was realized in one single organocatalytic step by an intramolecular Diels-Alder reaction of a synthesised tetraenal with an imidazolidinone-derivative as effective organocatalyst and TFA as co-catalyst. This reaction yielded the desired indane core with high selectivity, high endo/exo-selectivity and a surplus of enantiomers of 98% ee. As it turned out in the course of development of the total synthesis, not the initially explored organocatalytic transferhydration of a 1,2-unsaturated aldehyde in the presence of additional double bonds, but rather the reduction of an 1,2-unsaturated ester with magnesium successfully yielded the substrate for an organocatalyzed Henry reaction. The reaction also generated a new and interesting tricycle as a by-product, which occurs as a complex fragment in biologically active natural compounds. The preliminarily investigated selective nitroaldol reactions to generate the precursors of amaminol warrant further studies. In order to complete the synthesis by introducing the aminofunction, aminoacid derivatives from the chiral pool were used. Under optimised Masamune-Roush conditions a Horner-Wadsworth-Emmons reaction generated N-Boc-aminoketones. A Raney® nickel reduction of the conjugated double bond and, in the case of amaminol A, a syn-selective and, in the case of amaminol B, an anti-selective reduction resulted in N-Boc-amaminole A und B with very attractive yields and adequate selectivities. A comparison of the 1H-,13C-NMR-spectra of the synthesised N-Boc-amaminols and the naturally occurring amaminol derivatives confirmed the correct stereoconfiguration of the produced compounds. As a second project, the complete synthesis of the naturally occurring monoterpenoid (+)-Mitsugashiwalactone based on a biomimetic key step was realized. Starting out with succinalaldehyde, via only eight steps of reactions, the (+)-Mitsugashiwalactone could be synthesised with a total yield of 22%. It could be shown, that, similar to a Rauhut-Currier reaction, a symmetrical diendienal is transformed into a cyclopentene derivative in an organocatalytic 5-exo-trig-cyclization. In this reaction the required stereocenter is generated using diarylprolinolsilylethers as organocatalysts. In this set-up, under optimised conditions, enantioselectivities of up to 59% ee were achieved for the first time. The ample choices for expansion of the range of substrates and for additional optimisation of reactions that this dienamine-catalyzed cyclization provides, should be further explored in the future. Finally, preliminary investigations were undertaken of the feasibility of one-step proline-catalysed aldol reactions with subsequent palladium(II)-catalysed cyclization to form 2,6-disubstituted tetrahydropyranes. Direct aldol reactions of long-chain aldehydes as acceptors and cyclopentanons as donors result in 4,5-unsaturated syn- and anti-hydroxyketones with reasonable yields. Extensions of the aliphatic chains reduce the diastereoselectivities. For the first time, thus, 2,6-disubstituted tetrahydropyranes with a cyclization in the 2-position could be synthesised. These preliminary results of a palladium(II)-enabled cyclization of unsaturated hydroxyketones should facilitate further investigations, which could lead to selective syntheses of 2,6-cis-2,2´-syn- and 2,6-trans-2,2´-syn-tetrahydropyrane derivatives
Variations on the Author
Get PDF“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
Get PDFWe 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
Organokatalytische Synthesen biologisch aktiver Naturstoffe : Totalsynthesen von Amaminol A und B und (+)-Mitsugashiwalacton sowie Synthesen 2,6-disubstituierter Tetrahydropyranen
No full textAmaminol A and B are two diastereomeric 1,2-aminoalcohols of marine origin with a basic structure of a trans-fused bicyclononane. This work, for the first time, developed a complete synthesis of amaminol B, which, starting from 2E,4E-hepta-2,4-dien-1-ol and in a process of only eleven steps achieves a total yield of 21%. The overall concept of the complete synthesis of amaminol A and B is characterised by three key organocatalytic steps. The basic structure of amaminol A and B including the desired configuration of the four stereocenters was realized in one single organocatalytic step by an intramolecular Diels-Alder reaction of a synthesised tetraenal with an imidazolidinone-derivative as effective organocatalyst and TFA as co-catalyst. This reaction yielded the desired indane core with high selectivity, high endo/exo-selectivity and a surplus of enantiomers of 98% ee. As it turned out in the course of development of the total synthesis, not the initially explored organocatalytic transferhydration of a 1,2-unsaturated aldehyde in the presence of additional double bonds, but rather the reduction of an 1,2-unsaturated ester with magnesium successfully yielded the substrate for an organocatalyzed Henry reaction. The reaction also generated a new and interesting tricycle as a by-product, which occurs as a complex fragment in biologically active natural compounds. The preliminarily investigated selective nitroaldol reactions to generate the precursors of amaminol warrant further studies. In order to complete the synthesis by introducing the aminofunction, aminoacid derivatives from the chiral pool were used. Under optimised Masamune-Roush conditions a Horner-Wadsworth-Emmons reaction generated N-Boc-aminoketones. A Raney® nickel reduction of the conjugated double bond and, in the case of amaminol A, a syn-selective and, in the case of amaminol B, an anti-selective reduction resulted in N-Boc-amaminole A und B with very attractive yields and adequate selectivities. A comparison of the 1H-,13C-NMR-spectra of the synthesised N-Boc-amaminols and the naturally occurring amaminol derivatives confirmed the correct stereoconfiguration of the produced compounds. As a second project, the complete synthesis of the naturally occurring monoterpenoid (+)-Mitsugashiwalactone based on a biomimetic key step was realized. Starting out with succinalaldehyde, via only eight steps of reactions, the (+)-Mitsugashiwalactone could be synthesised with a total yield of 22%. It could be shown, that, similar to a Rauhut-Currier reaction, a symmetrical diendienal is transformed into a cyclopentene derivative in an organocatalytic 5-exo-trig-cyclization. In this reaction the required stereocenter is generated using diarylprolinolsilylethers as organocatalysts. In this set-up, under optimised conditions, enantioselectivities of up to 59% ee were achieved for the first time. The ample choices for expansion of the range of substrates and for additional optimisation of reactions that this dienamine-catalyzed cyclization provides, should be further explored in the future. Finally, preliminary investigations were undertaken of the feasibility of one-step proline-catalysed aldol reactions with subsequent palladium(II)-catalysed cyclization to form 2,6-disubstituted tetrahydropyranes. Direct aldol reactions of long-chain aldehydes as acceptors and cyclopentanons as donors result in 4,5-unsaturated syn- and anti-hydroxyketones with reasonable yields. Extensions of the aliphatic chains reduce the diastereoselectivities. For the first time, thus, 2,6-disubstituted tetrahydropyranes with a cyclization in the 2-position could be synthesised. These preliminary results of a palladium(II)-enabled cyclization of unsaturated hydroxyketones should facilitate further investigations, which could lead to selective syntheses of 2,6-cis-2,2´-syn- and 2,6-trans-2,2´-syn-tetrahydropyrane derivatives
Organocatalysed transformations of alpha,beta-unsaturated carbonyl compoundsthrough iminium ion intermediates
No full textThis chapter looks at how organocatalysed transformations of alpha,beta-unsaturated carbonyl compounds through iminium ion intermediates
Synthese eines 4-Desoxy-4-Fluor-Glucosyl-Derivats des phenolischen Glycolipids I von Mycobacterium Leprae und Synthese von C-Glycosiden durch Gold-katalysierte Oxidative Cyclisierung-Arylierung von Hex-5-En-2-Olen
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