Étude chimique de trois plantes médicinales camerounaises : Ficus Burretiana (Moraceae), Garcinia epunctata Stapf, Garcinia punctata Oliv (Guttiferae) et évaluation des activités antimicrobiennes de quelques composés isolés

Abstract

The present work deals with the extraction, isolation, structural elucidation and evaluation of the secondary metabolites isolated from the stem bark of Ficus burretiana (Moraceae), Garcinia epunctata Staft and Garcinia punctata Oliv (Guttiferae). Compounds were isolated from the extracts using chromatographic methods (CC, flash chromatography, analytical and preparative TLC) and their structures were determined by usual spectroscopic techniques (UV, IR, MS and NMR), and by comparison of their spectroscopic data with those reported in the literature. The chemical study of CH2Cl2/MeOH (1:1) and methanolic extracts of the stem bark of Ficus burretiana, Garcinia Epunctata Stapf and Garcinia punctata Oliv. led to the isolation of eighteen compounds. Sixteen of these compounds have been completely elucidated among which one is herein described for the first time; i.e. a benzophénone trivially named epunctanone. The fifteen other compounds were sorted into eight triterpenoids: lupeol, lupan-3-one, botulin, betulinic acid, 16β-hydroxylupeol, 29 norlupan-3,20-dione, 22,23,24,25,26,27- hexanordammarane-3,20-dione and fridelin; one xanthone: rheediaxanthone A; three benzophénones: 7-épiisogarcinol, isogarcinol, 7-épigarcinol, two steroids: stigmasterol, glucopyranoside-3-O-β-sitosterol; one benzophénone: 2,6-diméthoxy-p-benzoquinone. An O-propenylation transformed isogarcinol into another new benzophénone derivative named 14-O-allylisogarcinol; 13,14-di-O-allylisogarcinol. The biological activities were performed on compounds isolated from Garcinia epunctata Stapf and were evaluated on four microbial strains namely Neisseria gonorrhoeae, Mycobacterium aurum A+, Bodo caudatus, candida albicans. No compound was active against the protozoa Bodo caudatus. However, 7-epiisogarcinol displayed inhibitory activity against Candida albicans in the preliminary screenings, the minimum inhibitory concentration (MIC) value of 2mM was rather weak. Epunctanone, 7-epiisogarcinol and lupeol showed moderate activities against Mycobacterium aurum, Neisseria gonorrhoeae, and Candida albicans.