Investigation phytochimique et recherche d’activité biologique de deux espèces du genre Centaurea (Asteraceae)

Abstract

This work is devoted to the phytochemical and biological study of two species of the genus Centaurea (Asteraceae), endemic to Algeria and has never been studied before. They are Centaurea choulettiana Pomel and Centaurea fragilis Dur. The phytochemical investigation of cyclohexane, ethyl acetate and n-butanol extracts from the aerial parts of C. choulettiana and n-butanol extract of C. fragilis allowed the isolation and identification of 13 products. The structural elucidation of the isolated compounds was carried out by combining the various spectroscopic methods (UV, 1D & 2D NMR, HPLC/TOF-MS and GC/MS) as well as by comparing the results with the data of the literature. The analysis of essential oil (flowers) of C. choulettiana by the GC/MS technique, carried out for the first time, showed the presence of several chemical groups from which, phthalate (18.38%) followed by β-eudesmol (6.8%), 5-epoxysalvial-4(14)-ene (6.6%), caryophyllene oxide (4.28%), tricosane (3.31%), 7-epi-α-eudesmol (3.08%) and heptacosane. The antibacterial activity of this oil was determined against five bacterial strains according to the disk diffusion method, the results showed modest activity against all the strains. Quantification of the total polyphenols and total flavonoids of the EtOAc and n-BuOH (leaves and flowers) extracts of C. choulettiana was performed by colorimetric methods. This step showed a content of polyphenols and flavonoids more important in the AcOEt extract of the leaves. In order to identify and quantify the phenolic acids present in these extracts, chemical screening was performed by HPLC-TOF/MS, this revealed the presence of 9 phenolic acids in various amounts. The HPLC-TOF / MS analysis of the n-BuOH (leaves) extract of C. fragilis revealed the presence of 9 phenolic acids and 10 flavonoïds. The antioxidant activity of the EtOAc and n-BuOH (leaves and flowers) extracts of C. choulettiana was evaluated by the free radical scavenging method (DPPH) and the inhibition of lipid peroxidation (LPO). The EtOAc (leaves) extract exhibited the strongest effect with respect to the DPPH free radical (96.54%) and the inhibition of lipid peroxidation (64.17%). Concerning the antiproliferative activity, the results showed that the cyclohexane extract of C. choulettiana was the most active against HeLa cells (carcinoma of the human cervix), while the n-BuOH extract of C. fragilis was inactive in his unlevel doses.