Recherche et détermination structurale de molécules bioactives de plantes sahariennes – activités biologiques.

Abstract

This work is devoted to phytochemical and biological studies of two Algerian species, Pituranthos battandieri Maire (Apiaceae), an endemic plant of the Algerian-Moroccan Sahara and Frankenia thymifolia Desf. (Frankeniaceae) endemic of North Africa. The endemism of these species has encouraged us to conduct this work. Our objective consists of the isolation and structural determination of bioactive molecules starting from various extracts of these two plants as well as the in vitro evaluation of their antiparasitic, antibacterial and antioxidant activities. The cytotoxicity on murine macrophage of J 774 cell line of the antiparasitic compounds isolated from P. battandieri by bio-guided fractionation, separation and purification was also evaluated. The evaluation of the antiparasitic activity of the extracts from aerial parts and roots (taken separately) of P. battandieri against Leishmania amazonensis and donovani, Trypanosoma cruzi and Acanthamoeba castellanii showed significant antiparasitic properties. The bio-guided fractionation of the most active extracts (dichloromethane and petroleum ether from aerial parts and the roots, respectively) by various chromatographic techniques, led to the isolation of 14 active compounds on L. amazonensis and T. cruzi, of which 7 (P1-P7) have been identified. These compounds were 2 polyynes including 1 new as a natural product, 3 furanocoumarins, 1 monoterpene and 1 phenolic compound. Among the tested compounds, (-)-falcarindiol (P7) and (-)-panaxydiol (P6) exhibited significant antileishmanial and antitrypanosomal activities with low toxicity to J 774 macrophages. The antioxidant activities of the various extracts of this species were evaluated by several methods. The dichloromethane and ethyl acetate extracts of the aerial parts and petroleum ether of the roots showed remarkable antioxidant effects compared to the standards used. The phytochemical investigation of AcOEt and n-BuOH extracts from the aerial parts of F. thymifolia led to the isolation of 12 compounds, of which 7 flavonoids and a gallic acid derivative were characterized. The structural elucidation of the compounds was carried out by the combination of their spectroscopic data: (UV-Vis), 1D-NMR (1H, 13C and DEPT), 2D-NMR (COSY, HSQC, HMBC, and GOESY), high resolution mass spectrometry with EI and ESI ionization modes (HR-EI-MS and HRESIMS) and by comparison with literature data. The antioxidant powers of CHCl3, AcOEt and n-BuOH extracts from F. thymifolia as well as those of the isolated compounds F1, F2 and F6 were evaluated by several methods: radical DPPH, radical-cation ABTS, bleaching of β-carotene, radical- anion superoxide, ferrous chelating power, CUPRAC and FRAP. The results clearly indicated high antioxidant potentials of the extracts and compounds tested. These results were in good agreement with the total polyphenol and flavonoid contents data. Moreover, the results of the evaluation of the antiparasitic activity showed that the AcOEt extract showed a remarkable antiparasitic effect compared to n-BuOH and CHCl3 extracts, against A. castellanii and L. amazonensis parasites. While, AcOEt and n-BuOH extracts showed moderate antibacterial activity on the bacterial strains tested.