Isolement et détermination structurale de métabolites secondaires de deux plantes sahariennes : Asteriscus graveolens (Forsk.) DC. (Asteraceae) et Crotalaria vialattei Batt. (Fabaceae).

Abstract

This work is devoted to the phytochemical study of two endemic Saharan plants, Asteriscus graveolens (Forsk.) DC. and Crotalaria vialattei Batt. belonging respectively, to the Asteraceae and Fabaceae families. These two families are renowned for their richness in bioactive secondary metabolites. This study led to the isolation and identification of 25 natural compounds, among which, 9 were isolated from the chloroform phase of the hydroalcoholic extract of the aerial parts (leaves and flowers) of Asteriscus graveolens: 6 sesquiterpenes of the humelene type, among which 3 were new natural products, that we report for the first time in the literature. This type of molecule stands out as typical compounds of the Asteraceae family and the Asteriscus genus. From chloroform and ethyl acetate extracts of the aerial parts (leaves) of the species Crotalaria vialattei Batt. 16 secondary metabolites, mostly flavonoids and phenolic compounds, have been identified. Among these compounds, 5 flavones including two prenylated and 3 isoflavones, in addition to a chalcone, 2 pentacylic triterpenes with a lupane skeleton, 1 sterol and 4 phenolic compounds. All of these compounds are isolated for the first time from this species. The structural elucidation of the isolated compounds was achieved through the analysis of high resolution mass spectra using the electrospray ionization mode (HRESI-MS), 1D NMR (1H, 13C and DEPT) and 2D NMR (COSY, HSQC , HMBC, NOESY and ROESY), UV-Vis and IR spectrophotometry, single-crystal X-ray diffraction, in addition to the optical rotation measurements and comparison with data from the literature. This work has been the subject of a published article and two other publications in progress.