Etude phytochimique et évaluation des activités antibactériennes des feuilles De Garcinia epunctata Stapf (Clusiaceae)

Abstract

Natural substances occupy a more and more important place in therapeutic. In fact, medicinal plants constitute real chemical factories from which maximum profit must be made for the well-being of the population. This work comes to add to a long series of studies on medicinal plants and natural extracted substances. Its objective is to reveal new molecules and to highlight their antibacterial activities. To do this, we have choosen the medicinal plant Garcinia epunctata, because of its antibacterial potential (Tih et al., 2000). The phytochemical investigation of the ethyl acetate extract of the leaves of G. epunctata, led to the isolation of fifteen secondary metabolites. They are: two new phenolic glycosides (Epunctoside A and B), one known phenolic glycoside (Lanceoloside A), one triterpenic acid (butelinic acid), one triterpen (lupeol), four steroid derivatives (stigmasterol, β-sitosterol, stigmasterol 3-O-β-D-glucopyranoside and β-sitostérol 3-O- β-D- glucopyranoside), two flavonoid derivatives (lutéoline-7-O-glucoside and quercétine-7-O- glucoside) and four biflavonoids (Amentoflavone, robustaflavone, 4′-O-méthylamentoflavone and 4′-O-méthylrobustaflavone). Their chemical structures were established using spectroscopic methods (MS, UV, IR, 1D and 2D H-NMR, 1D and 2D C-NMR) and also by comparing some spectra with previous data. The ethyl acetate extract as well as four pure compounds (β-sitosterol, stigmasterol, epunctoside A and B) were subjected to antibacterial screening, by disc diffusion and microdilution method, against five bacteria strains (Pseudomonas aeruginosa, Salmonella typhimurium, Salmonella enteritidis, Staphylococcus aureus and Esherichia coli). These bacteria are responsible for urinary infections, breathing infections, skin infections and gastroenteritis disorder. The ethyl acetate extract recorded diameters of zone of inhibition ranging from 15 to 18 mm, corresponding to high activity. All the four pure compounds recorded moderate activity with diameter of zone of inhibition ranging from 8 to 10 mm. The extract recorded low MIC values ranging from 0.125 to 1 mg/mL meanwhile, the MIC of pure compounds are between 0.125 and 0.5 mg/mL. The MBC values for the extract are closer to the MIC values. Suggesting that the extract has a bactericidal effect on all the bacteria strains, except P. aerugynosa on which the effect of the extract is bacteriostatic. The pure compounds recorded high MBC values of which the ratios MBC/MIC are greater than 4. This result shows that the pure compounds have a bacteriostatic effect on each of the bacteria strain. The results also justify the use of the leaves of G. epunctata in folk medecine to treat gastroenteritis infections and urinary infections. However, more indepth studies are necessary