Investigation phytochimique de plantes médicinales sahariennes – Activité biologique

Abstract

This work is devoted to the phytochemical and biological study of two endemic Saharan medicinal plants, Heliotropium bacciferum Forssk. (Boraginaceae) and Lifago dielsii Schwein. & Musch. (Asteraceae). This phytochemical study led the isolation and identification of twenty products, seventeen of which were monoterpenes megastigans and phenolic type, were obtained from the chloroform and methanol extracts of the aerial parts of Heliotropium bacciferum Forssk. While three glycosylated flavonoids were obtained from the ethyl acetate extract of the aerial parts of Lifago dielsii Schwein & Musch. The structures of the isolated products were elucidated mainly by the use of NMR techniques (1H, 13C, COSY, HSQC and HMBC), UV spectrophotometry and by comparison with those reported in the literature. The quantification of the total phenolic content of the MeOH extract of H. bacciferum was carried out using the Folin-Ciocalteu method. This step showed a polyphenolic content of 68.0 mgGAE/g extract. This extract was evaluated for its antioxidant activity towards the free radical DPPH and the radical ABTS. The results showed that this extract exhibited a significant activity and is dependent on the concentration in vitro with respect to the DPPH radicals (IC50 70.912 μg/ml), and ABTS (IC50 1.466 μg/ml), related to the presence of the phenolic derivatives. Both extracts and some isolated products of H. bacciferum were tested for their cytotoxic effect in human cancer cell lines (HCT-116, DLD1 and HDFa). Only the chloroform extract showed a significant and concentration-dependent inhibitory effect on the growth of IC50 treated cancer cell lines of 0.095 mg/ml on HCT116 and 0.062 mg/ml on DLD1. The quantification of total phenols and total flavonoids contents of the CHCl3, EtOAc, nBuOH extracts and of the methanol insoluble part (MeOH) of the aerial parts of L. dielsii was carried out using colometric methods. This study showed a phenolic content more important in the EtOAc extract. However, total flavonoids content was higher in n-BuOH extract (88.81%). The antioxidant activity of L. dielsii extracts was evaluated by the DPPH free radical scavenging and the lipid peroxidation inhibition (LPO) assays. The EtOAc extract has the strongest effect on DPPH with (IC50 = 47.80 ± 2.20 μg/ml) and the inhibition of lipid peroxidation (IC50 = 113.24 ± 0.65 μg/ml).