Métabolites secondaires issus de Rhabdophyllum arnoldianum (De Wild. & T. Durand) Tiegh, Rhabdophyllum affine (Hook. F.) Tiegh (Ochnaceae) et Cassia arereh Delile (Fabaceae) : Détermination de leurs potentiels antimicrobiens et cytotoxiques

Abstract

The aim of this work was to identify components with cytotoxic and antimicrobial properties derived from plants extracts of the Ochnaceae and Fabaceae families, belonging to the Cameroonian flora, in order to fight antimicrobial resistance and improve selectivity index of cytotoxic drugs. Our investigations were carried out on three plants: Cassia arereh Delile, Rhabdophyllum arnoldianum (De Wild. & T. Durand) Tiegh et Rhabdophyllum affine (Hook. F.) Tiegh. Based on phytochemical studies carried out using liquid chromatographic methods on extracts of these plants, we isolated and characterized twenty (20) compounds including four (4) new compounds: two (2) flavonoids glycosides of the flavone type [arnoldioside A (150) and arnoldioside B (151)], isolated from R. arnoldianum, one (1) lupane-type triterpene [cassiaric acid (161)] as well as one (1) ceramide [cassiaramide (165)], isolated from C. arereh. The sixteen (16) known compounds were grouped into different classes including five (5) flavonoids [three (3) flavones : Apigenin (147); isoswertisin (148) ; 2ʺ-O-acétyl-7-O-méthylvitexin (149) and two (2) flavanols : Catechin (153) and epicatechin (152)], one (1) isoflavone [4ʹ,5-dimethoxy-6,7-methylenedioxyisoflavone (157)], two (2) biflavonoids [Amentoflavone (156) and Rhusflavone (155)], five (5) triterpenes [Lupeol (157), Betulinal (158), Betulinic acid (159), Betulin (160), Ceanothic acid (162)], one (1) phytosterol (3-O-β-D-glucopyranosyl-β-sistosterol) (164), one (1) alkaloid [serotobenin (166)] and one (1) benzoylglycoside [Lanceoloside A (163)]. The structures of all these compounds were elucidated by a rigorous interpretation of their spectral data, in particular NMR 1D (1H and 13C) and 2D (COSY, HMBC, HSQC, NOESY) in conjunction with mass spectrometry such as ESI. Regarding biological analysis, the crude extracts and some of the isolated pure compounds were evaluated for their antimicrobial susceptibility on nine microbial strains (Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Bacillus cereus, Bacillus subtilis, Klebsiella pneumoniae, Pseudomonas aeruginosa, Haemophilus influenza, Candida albicans) in vitro on culture media. Also, these plants crude extracts and the pure isolated compounds were also investigated for their cytotoxic activities on one mammary (MCF-7) and one cervical tumor cell (HeLa). With respect to the antibacterial susceptibility, the new triterpene [cassiaric acid (161)] demonstrated a microbial activity against the bacterial strain Pseudomonas aeruginosa, with an MBC of 15.63 μg/mL similar to the reference antibiotic, levofloxacin that was used. In terms of cytotoxic activity, cassiaric acid (161) also demonstrated the best cytotoxic activity against the Hela cell lines, with an IC50 concentration of 19.0 μg/mL after a period of 48 hours.