1,721,025 research outputs found
Amino acid-sesquiterpene lactone conjugates from the aerial parts of Centaurea pungens and evaluation of their antimicrobial activity
No full textTwo new amino acid-sesquiterpene lactone conjugates, named centaureolide A (1) and centaureolide B (2) along with a germacrane derivative (3), five flavonoids (4–8) and one quinic acid derivative (9) have been isolated from the aerial parts of Centaurea pungens (Asteraceae). Their structures were established by a combination of one- and two-dimensional NMR techniques, and mass spectrometry. The never reported sesquiterpene lactones have been determined as germacrane derivatives (1 and 2) characterized by the unusual occurrence of a proline moiety. In order to validate the use of the extract of C. pungens in folk medicine, the antimicrobial activity of the isolated compounds against the Gram-positive strains Bacillus cereus, Staphylococcus aureus and Listeria innocua and the Gram-negative strains Pseudomonas aeruginosa and Pseudomonas fragi was evaluated
Chemical constituents of the aerial parts of santolina chamaecyparissus and evaluation of their antioxidant activity
No full textSantolina chamaecyparissus is an aromatic evergreen herb growing in North Africa and near the Mediterranean coasts of Southern Europe. Literature data focused mainly on the investigation of the essential oil content of the aerial parts of S. chamaecyparissus, but few is known on the chemical composition of its polar extract. Total phenolic content was determined by the Folin-Ciocalteau method and the antioxidant activity of the n-butanol and chloroform fractions of S. chamaecyparissus was tested by Trolox equivalent antioxidant capacity (TEAC) and diphenyl-2-picrylhydrazyl radical (DPPH) assays. Difference of the phenolic content and of the antioxidant activity between the two extracts prompted us to investigate their chemical composition. Five compounds, eupatilin (1), circimaritin (2), 4'-hydroxy-5,6,7-trimethoxyflavone (3), 1,3-propanediol,2-amino 1-(4-hydroxy-3-methoxyphenyl) (4) and luteolin (5) have been isolated from the chloroform extract, while the investigation of butanolic extract led to the isolation of seven compounds, prunasin (6), luteolin 7-O-Î2-D-glucopyranoside (7), syringoside (8), junipeionoloside (9), citroside A (10), lonicerin (11) and apigenin 7-O-Î2-D-neohesperidoside (12). Their structures were elucidated by extensive spectroscopic methods including 1D- (1H, 13C and TOCSY) and 2D-NMR (DQF-COSY, HSQC, HMBC) experiments as well as ESIMS analysis
Chemical constituents and in vitro anti-inflammatory activity of Cistanche violacea Desf. (Orobanchaceae) extract
No full textA new iridoid (1) and a new phenylethanoid glycoside (4), together with five known compounds (2, 3, 5, 6 and 7), were isolated for the first time from the ethyl acetate soluble part of the hydroalcoholic extract of the aerial parts of Cistanche violacea Desf. (Orobanchaceae), an endemic species of the North of the Sahara. The structures of these compounds have been elucidated on the basis of extensive 2D NMR spectroscopic analysis, including COSY, TOCSY, NOESY, HSQC, CIGAR-HMBC, H2BC and HSQC-TOCSY. All compounds were isolated from C. violacea for the first time. The anti-inflammatory activity of the EtOAc extract of C. violacea, was investigated by using human red blood cell (HRBC) membrane stabilization and inhibition of the albumin denaturation method. This study demonstrates, for the first time the effectiveness of C. violacea in combating inflammation, this might be believed to be influenced by the synergistic action of the above isolated compounds. The present study suggests that C. violacea would serve as a source for the discovery of novel anti-inflammatory agents.A new iridoid (1) and a new phenylethanoid glycoside (4), together with five known compounds (2, 3, 5, 6 and 7), were isolated for the first time from the ethyl acetate soluble part of the hydroalcoholic extract of the aerial parts of Cistanche violacea Desf. (Orobanchaceae), an endemic species of the North of the Sahara. The structures of these compounds have been elucidated on the basis of extensive 2D NMR spectroscopic analysis, including COSY, TOCSY, NOESY, HSQC, CIGAR-HMBC, H2BC and HSQC-TOCSY. All compounds were isolated from C. violacea for the first time. The anti-inflammatory activity of the EtOAc extract of C. violacea, was investigated by using human red blood cell (HRBC) membrane stabilization and inhibition of the albumin denaturation method. This study demonstrates, for the first time the effectiveness of C. violacea in combating inflammation, this might be believed to be influenced by the synergistic action of the above isolated compounds. The present study suggests that C. violacea would serve as a source for the discovery of novel anti-inflammatory agents
Phytochemical investigation of Volutaria lippii and evaluation of the antioxidant activity
No full textVolutaria lippii (L.) Cass. ex Maire, syn. Centaurea lippii (L.), (Asteraceae) is a plant from the central region of Algeria, considerably distributed in all Mediterranean areas. Herein, the antioxidant activity of the three derived fractions [chloroform (CHCl3), ethyl acetate (EtOAc) and n-butanol (n-BuOH)] of the 70% methanol extract of the aerial parts (leaves and flowers), was assessed by using CUPRAC, ABTS, DPPH free radical scavenging, and beta-carotene bleaching methods. The results obtained allowed to guide the fractionation of EtOAc and n-BuOH fractions by CC followed by purification by TLC and reverse phase HPLC. A guaianolide glucoside, 3 beta-hydroxy-11 beta,13-dihydrodehydrocostuslactone 8 alpha-O-(6'-acetyl-beta-glucopyranoside) (1), never reported in the literature, was isolated together with other known compounds (2-14). Their structures were elucidated by the extensive use of 1 D- and 2 D-NMR experiments along with ESI-MS analyses and with comparison with literature data
Heliotropium bacciferum Forssk. (Boraginaceae) extracts: chemical constituents, antioxidant activity and cytotoxic effect in human cancer cell lines
No full textHeliotropium bacciferum (Boraginaceae) is a perennial herb, growing in the Bechar region of Algeria, where it is traditionally used for skin diseases and tonsillitis. Herein, we report the isolation and characterization of sixteen secondary metabolites from the aerial part extracts. They include a sterol (1), megastigman type nor-isoprenoids (2, 3, 4, 6, 8, 10), C-11 terpene lactones (5 and 9), and a monoterpene (7) from the chloroform extract (HB-C); monoterpene glucoside (14), and phenolic compounds (11â13, 15, 16) from the methanol one (HB-M). Their structures were elucidated by spectroscopic methods including 1D and 2D NMR experiments, and ESIMS analysis. HB-M showed a significant and concentration dependent scavenging activity in vitro against the radicals DPPH and ABTS, related to the phenol derivatives (11â13, and 15â16), and HB-C inhibited the growth of colon cancer cell lines, mainly for the presence of the antiproliferative C-11 terpene lactones (5 and 9)
Chemical composition and antioxidant activity of a polar extract of Thymelaea microphylla Coss. et Dur
Full text linkThymelaea microphylla Coss. et Dur. (Thymelaeaceae) is a rare medicinal plant endemic to Algeria. In order to continue our studies on this species, herein we report the isolation and characterisation of 20 compounds from a hydroalcoholic extract (EtOH-H2O 7:3) of the aerial parts. They include monoterpene glucosides (1-3), phenolic acid derivatives (4, 8 and 9), phenylpropanoid glucosides (5 and 6), flavonoids (7, 10 and 11), a benzyl alcohol glucoside (12), ionol glucosides (13-16), lignans (17-19) and a bis-coumarin (20). All the structures were elucidated by spectroscopic methods including 1D and 2D NMR experiments, as well as ESI-MS analysis. Moreover, the extract of T. microphylla showed a significant and concentration-dependent free radical-scavenging activity in vitro, correlated to the presence of phenolic and chlorogenic acid derivatives (8, 9 and 4)
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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