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Saponins of Allium elburzense
No full textA phytochemical investigation of the bulbs of Allium elburzense has been undertaken, leading to the isolation of 13 furostanol and spirostanol saponins, eight of which are new, namely, elburzensosides A1/A2 (1a/1b), B1/B2 (2a/2b), C1/C2 (3a/3b), and D1/D2 (4a/4b). On the basis of spectroscopic analysis, mainly 2D NMR and mass spectrometry, and chemical methods, the structures of the new compounds were determined as furost-2alpha,3beta,5alpha,6beta,22alpha-pentol 3-O-beta-D-glucopyranosyl 26-O-beta-D-glucopyranoside (1a), furost-2alpha,3beta,5alpha,6beta,22alpha-pentol 3-O-beta-D-glucopyranosyl-(1-->4)-O-beta-D-glucopyranosyl] 26-O-beta-D-glucopyranoside (2a), furost-2alpha,3beta,5alpha,22alpha-tetrol 3-O-beta-D-glucopyranosyl 26-O-beta-D-glucopyranoside (3a), and furost-2alpha,3beta,5alpha,22alpha-tetrol 3-O-[beta-D-xylopyranosyl-(1-->3)-O-beta-D-glueopyranosyl-(1-->4)-O-beta -D-galactopyranosyl 26-O-beta-D-glucopyranoside (4a), and the corresponding epimers at position 22 (1b-4b). Along with these compounds we have isolated the corresponding 22-O-methyl derivatives that we consider extraction artifacts. All the new elburzensosides A1/A2-D1/D2 possess as a common structural feature an OH-5alpha that is rare among furostanol saponins. The reported compounds have been isolated in large amounts, and this makes A. elburzense a prolific producer of saponins of the furostanol and spirostanol types
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
The sapogenin atroviolacegenin and its diglycoside atroviolaceoside from Allium atroviolaceum
No full textA phytochemical analysis of broadleaf wild leek, Allium atroviolaceum, has led to the isolation of a new sapogenin, named atroviolacegenin (1, Chart 1), and its diglycoside derivative, named atroviolaceoside (2), both possessing a hydroxyl group at C-27, a rare feature among sapogenins and saponins. On the basis of chemical and spectroscopic analyses, including 2D NMR spectroscopy and mass spectrometry, the structures of the new compounds were elucidated as (25R)5 alpha-spirostan-2 alpha,3 beta,6 beta,27-tetrol (1) and (25R)-5 alpha-spirostan-2 alpha,3 beta,6 beta,27-tetrol 3-O-beta-D-glueopyranosyl-(1 -> 4)-O-beta-D-galactopyranoside (2). These compounds are accompanied by three known spirostanol and furostanol saponins. In addition, 4,4'-dihydroxy-3-methoxychalcone, p-coumaroyl-N-tyrosine, and p-feruloyl-N-tyrosine have been found in the flowers and bulbs. Atroviolacegenin and atroviolaceoside were assayed to evaluate their antispasmodic activity in the guinea-pig isolated ileum and the data compared to those previously found for tropeosides (3a/3b and 4a/4b) from Tropea red onion bulbs. The absence of activity for both atroviolacegenin and atroviolaceoside highlighted the key role of the furostanol-type aglycone moiety for antispasmodic activity
Structure-activity relationships for Saponins from Allium hirtifolium and Allium elburzense and their antispasmodic activity
No full textA phytochemical study of Allium hirtifolium Boiss flowers has led to the isolation of high amounts of six new furostanol and spirostanol saponins, named hirtifoliosides A1/A2 (1a/1b), B(2), C1/C2 (3a/3b), and D (4) along with three known spirostanol saponins, alliogenin 3-O-beta-D-glucopyranoside, gitogenin 3-O-beta-D-glucopyranosyl-(1 -> 4)-O-beta-D-glucopyranoside, and agapanthagenin 3-O-beta-D-glucopyranoside. High concentrations of the following known flavonol glycosides have been isolated from both flowers and bulbs: kaempferol 3-O-beta-D-rhamnopyranosyl-(1 -> 2)-glucopyranoside, kaempferol 3-O-beta-D-glucopyranosyl-(1 -> 4)-glucopyranoside, kaempferol 3-O-glucopyranoside, kaempferol 7-O-glucopyranoside. The isolated saponins along with the four saponins elburzensosides A1/A2 and C1/C2 and the sapogenin agapanthagenin, previously described from A. elburzense, have been subjected to biological assays for evaluating possible antispasmodic activity in the guinea-pig isolated ileum. The obtained results served as a basis for the establishment of structure-activity relationships within this class of antispasmodic agents. They highlight the positive effects of a hydroxyl group at position 5 and of a glucose unit at position 26 and demonstrate the detrimental effects of both a hydroxyl group at position 6 and of a glucose unit at position 3. Among the tested compounds, elburzensosides C1/C2 and agapanthagenin showed the highest activity in reducing induced contractions as measured by the reduction of histamine release by about 50%. The observed effect therefore contributes to the explanation of the traditional use of onion and garlic in the treatment of disturbances of the gastrointestinal tract
Saponins from Allium minutiflorum with antifungal activity
No full textThree saponins, named minutoside A (1), minutoside B (2), minutoside C (3), and two known sapogenins, alliogenin and neoagigenin, were isolated from the bulbs of Allium minutiflorum Regel. Elucidation of their structure was carried out by comprehensive spectroscopic analyses, including 2D NMR spectroscopy and mass spectrometry. The structures of the new compounds were identified as (25R)-furost-2 alpha,3 beta,6 beta,22 alpha,26-pentaol 3-O-[beta-D-Xyl0pYranosyl-(1 -> 3)-O-beta-D-glucopyranosyl-(14)-O-beta-D-galactopyranosyl] 26-O-beta-D-glucopyranoside (1), (25S)-spirostan-2 alpha,3,60-triol 3-O-beta-D-xylopyranosyl-(1 -> 3)-O-beta-D-glucopyranosyl-(1 -> 4)-O-D-D-galactopyranoside (2), and (25R)-furost-2 alpha,3 beta,5 alpha,6 beta,22 alpha,26-esaol 3-O-[beta-D-xylopyranosyl-(1 -> 3)-O-beta-D-glucopyranosyl-(1 -> 4)-O-beta-D-galactopyranosyl] 26-O-beta-D-glucopyranoside (3). The isolated compounds were evaluated for their antimicrobial activity. All the novel saponins showed a significant antifungal activity depending on their concentration and with the following rank: minutoside B > minutoside C >> minutoside A. No appreciable antibacterial activity was recorded. The possible role of these saponins in plant-microbe interactions is discussed. (c) 2006 Elsevier Ltd. All rights reserved
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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