Isolement et détermination structurale de métabolites secondaires d’espèces des genres Santolina et Centaurea (Asteraceae) - Activités biologiques.

Abstract

This work is part of the research program established by our research unit which consists in the phytochemical investigation of Algerian medicinal plants belonging to families known for their richness in secondary metabolites with potential biological activities. In this context, two species were selected: Santolina chamaecyparissus and Centaurea pungens, given their belonging to the family Asteraceae whose richness in bioactive compounds is well established. Known mainly for their essential oils, the aerial parts of S. chamaecyparissus (leaves + flowers) were macerated in 70% ethanol. After filtration, concentration and dilution with distilled water, the obtained hydroalcoholic extract is subjected to successive extractions by solvents of increasing polarity (CHCl3, AcOEt and n-BuOH) to give the three corresponding derivative extracts. Our experiments concerned the CHCl3 and n-BuOH extracts and focused on the determination of the total phenols of the two extracts and then the evaluation of their antioxidant activity by the DPPH radical reduction and TEAC tests. The results showed that the n-BuOH extract is richer in phenolic compounds and is better antioxidant than the CHCl3 extract in the DPPH radical scavenging assay with vitamin C as positive control. In the TEAC test, the results were in agreement with those of the DPPH radical test, in fact the n-BuOH extract showed a significant and similar activity to that of quercetin 3-O-glucoside used as positive control. Following these encouraging results, both extracts were subjected to chromatographic techniques and 15 compounds were isolated. The structures of 14 of these compounds were determined. These are 5 flavone aglycones including 4 methoxylated; 3 glycosylated flavones, 2 of which were new for Santolina genus; 2 megastigmane glucosides new for Asteraceae family; 2 phenylpropanoids new for the genus Santolina and 2 cyanogenic compounds also new for the genus Santolina. The phytochemical investigation of Centaurea pungens (Flowers) conducted by similar methods as reported for S. chamaecyparissus, allowed the isolation of 9 pure products: 3 sesquiterpene lactones, 2 of which were described for the first time in the literature, 2 methoxylated flavones, 3 glucosylated flavones and a derivative of quinic acid. In order to validate the use of C. pungens in traditional medicine, the antimicrobial activity of the 9 isolated compounds was assessed against Gram-positive strains: Bacillus cereus, Staphylococcus aureus and Listeria innocua, and Gramnegative strains: Pseudomonas aeruginosa and Pseudomonas fragi.