Justin Komguem

Antibacterial activity of some natural products against bacteria expressing a multidrug-resistant phenotype

The present study assessed the antimicrobial activities of various natural products belonging to the terpenoids, alkaloids and phenolics against a collection of Gram-negative multidrug-resistant (MDR) bacteria. The results demonstrated that most of the compounds were extruded by bacterial efflux pumps. In the presence of the efflux pump inhibitor phenylalanine arginine β-naphthylamide (PAβN), the activities of laurentixanthone B (xanthone), plumbagin (naphthoquinone), 4-hydroxylonchocarpin (flavonoid) and MAB3 (coumarin) increased significantly against all studied MDR bacteria. Laurentixanthone B, 4-hydroxylonchocarpin and MAB3 contained the same pharmacophoric moiety as plumbagin. This study indicates that the AcrAB-TolC (Enterobacteriaceae) and MexAB-OprM (Pseudomonas aeruginosa) efflux pumps are involved in resistance of Gram-negative bacteria to most of the natural products.

Cytotoxicity of Natural Compounds Isolated from the Seeds of Garcinia afzelii

The new compounds guttiferone O ( 1) and 3-methoxycheffouxanthone ( 2) have been isolated from the seeds of Garcinia afzelii Engl., together with nine known compounds: 2-hydroxy-1,7-dimethoxyxanthone ( 3), smeathxanthone A ( 4), 1,5-dihydroxyxanthone ( 5), 1,6-dihydroxy-5-methoxyxanthone ( 6), cheffouxanthone ( 7), 1,3,5-trihydroxyxanthone ( 8), smeathxanthone B ( 9), isoxanthochymol ( 10) and guttiferone E ( 11). Their structures were elucidated by means of 1D and 2D-NMR techniques. All the isolates showed high cytotoxic activity and were found inactive when tested against HIV and influenza viruses.

Antimalarial activity of extract and norbergenin derivatives from the stem bark of Diospyros sanza-minika A. Chevalier (Ebenaceae)

The methanol extract from the stem bark of Diospyros sanza‐minika as well as five norbergenin derivatives isolated from this crude extract were evaluated for their in vitro activity against Plasmodium falciparum K1 and cytotoxicity on MRC‐5 cells. 4‐O‐(3′‐methylgalloyl)norbergenin was found to be the most potent compound (IC50 0.6 μg/mL; CC50 24.7 μg/mL), followed by 4‐O‐galloylnorbergenin (IC50 3.9 μg/mL; CC50 > 64 μg/mL) and 11‐O‐p‐hydroxy‐benzoyl‐norbergenin (IC50 4.9 μg/mL; CC50 > 64 μg/mL). Norbergenin and 4‐O‐syringoylnorbergenin were inactive (IC50 > 32 μg/mL; CC50 > 64 μg/mL). The antimalarial activity of the pure constituents and of the methanol extract from the stem bark of Diospyros sanza‐minika is reported for the first time. The results provide interesting baseline information for the potential use of the crude extract well as some of the isolated compounds in the search for novel antimalarial compounds. Copyright