Ghislain W. Fotso

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.

Prenylated arylbenzofuran derivatives from Morus mesozygia with antioxidant activity

Five prenylated arylbenzofurans, moracins Q-U, were isolated from Morus mesozygia (Moraceae). Their structures were elucidated on the basis of spectroscopic evidence. Along with these compounds, 3beta-acetoxyurs-12-en-11-one, marsformoxide, moracin C, moracin M, moracin K, artocarpesin, cycloartocarpesin, morachalcone A were also isolated. Four of the five compounds, (moracins R-U) displayed potent antioxidant activity.

Antimicrobial activities of the methanol extract and compounds from Artocarpus communis (Moraceae)

BackgroundArtocarpus communis is used traditionally in Cameroon to treat several ailments, including infectious and associated diseases. This work was therefore designed to investigate the antimicrobial activities of the methanol extract (ACB) and compounds isolated from the bark of this plant, namely peruvianursenyl acetate C (1), α-amyrenol or viminalol (2), artonin E (4) and 2-[(3,5-dihydroxy)-(Z)-4-(3-methylbut-1-enyl)phenyl]benzofuran-6-ol (5).MethodsThe liquid microdilution assay was used in the determination of the minimal inhibitory concentration (MIC) and the minimal microbicidal concentration (MMC), against seven bacterial and one fungal species.ResultsThe MIC results indicated that ACB as well as compounds 4 and 5 were able to prevent the growth of all tested microbial species. All other compounds showed selective activities. The lowest MIC value of 64 μg/ml for the crude extract was recorded on Staphylococcus aureus ATCC 25922 and Escherichia coli ATCC 8739. The corresponding value of 32 μg/ml was recorded with compounds 4 and 5 on Pseudomonas aeruginosa PA01 and compound 5 on E. coli ATCC 8739, their inhibition effect on P. aeruginosa PA01 being more than that of chloramphenicol used as reference antibiotic.ConclusionThe overall results of this study provided supportive data for the use of A. communis as well as some of its constituents for the treatment of infections associated with the studied microorganisms.

Virtualizing the p-ANAPL Library: A Step towards Drug Discovery from African Medicinal Plants

Background Natural products play a key role in drug discovery programs, both serving as drugs and as templates for the synthesis of drugs, even though the quantities and availabilities of samples for screening are often limitted. Experimental approach A current collection of physical samples of > 500 compound derived from African medicinal plants aimed at screening for drug discovery has been made by donations from several researchers from across the continent to be directly available for drug discovery programs. A virtual library of 3D structures of compounds has been generated and Lipinski’s “Rule of Five” has been used to evaluate likely oral availability of the samples. Results A majority of the compound samples are made of flavonoids and about two thirds (2/3) are compliant to the “Rule of Five”. The pharmacological profiles of thirty six (36) selected compounds in the collection have been discussed. Conclusions and implications The p-ANAPL library is the largest physical collection of natural products derived from African medicinal plants directly available for screening purposes. The virtual library is also available and could be employed in virtual screening campaigns.

Flavonoids and Related Compounds from the Medicinal Plants of Africa

Bioactive natural molecules such as flavonoids are considered important for their biological activity. Flavonoids are a group of secondary metabolites derived from the phenylpropanoid pathway. There is strong evidence based on epidemiological studies that correlates consumption of fruits and vegetables with reduced risk in terms of number of cancers. The main flavonoids found in vegetables are quercetin and kaempferol. While plant-based medicines containing phenylpropanoid-derived active components have long been used by humans, the benefits of specific flavonoids and other phenylpropanoid-derived compounds to human health and their potential for long-term health benefits have been recognized only more recently. In this part of the review, we discuss the diversity and biosynthetic origins of phenylpropanoids and particularly of the flavonoid natural products. Flavonoids are one of the classes of heterocyclic natural compounds that are widely distributed in plant as glycosides or as free aglycones. In this chapter, we review the flavonoids isolated in African medicinal plants, their biological properties, and their biosynthesis in plants.

Secondary metabolites with antiproliferative effects from Albizia glaberrima var glabrescens Oliv. (Mimosoideae)

Abstract A new 5-dehydroxyflavan, namely Albiziaflavan B or (+)-(2R, 3S, 4R)-3′,4′, 7-trihydroxy-4-methoxy-2,3-trans-flavan-3,4-trans-diol (1) was isolated from the root bark of Albizia glaberrima, together with six known compounds including three flavans: (+)-mollisacacidin (2), (+)-fustin (3) and butin (4); two steroids: chondrillasterol (5) and chondrillasterone (6), and a triterpenoid: lupeol (7). The structure of 1 was established by detailed analysis of its spectroscopic data, especially 1D and 2D NMR spectra, HRESIMS and CD data. Compounds 1–6 were assayed for their antiproliferative effects on two human cancer cells, HeLa at 50 μM (n = 2) and HL60 at 20 μM (n = 2). Compound 3 and 4 were the most active on HL60 with IC50 of 8.1 and 8.3 μM, respectively. Compound 6 was the most active with an IC50 of 4.6 μM on HeLa.

Hemisynthesis and Spectroscopic Characterization of Three New Chalcone Derivatives from Dorstenia barteri

The hemisynthesis of three new chalcones, namely kenzanol, kelianol A, and kelianol B, from Dorstenia barteri (Moraceae) is described here for the first time. The synthetic pathways employed in this work involved the pyrolysis and catalytic hydrogenation of readily available and starting materials, 4-hydroxylonchocarpin and isobavachalcone, two major constituents of the herbaceous plant D. barteri. The structural elucidation of all the compounds was done by mass spectrometry, IR, UV, 1D and 2D NMR analysis, and also by comparison with previous reports.

Thonningiiflavanonol A and thonningiiflavanonol B, two novel flavonoids, and other constituents of Ficus thonningii Blume (Moraceae).

Abstract A phytochemical study of Ficus thonningii has led to the isolation of two previously unreported compounds, thonningiiflavanonol A and thonningiiflavanonol B together with 16 known compounds: shuterin, naringenin, syringic acid, p-hydroxybenzoic acid, genistein, 5,7,3′,4′,5′-pentahydroxyflavanone, luteolin, methylparaben, aromadendrin, garbanzol, dihydroquercetin, 5,7,3′-trihydroxyflavanone, β-sitosterol, sitosterolglucoside, lupeol acetate, and taraxerol. Their structures were elucidated on the basis of spectroscopic data. The new compounds and extracts displayed potent antioxidant activity.