Bathelemy Ngameni

Antimicrobial activity of the crude extracts and compounds from Ficus chlamydocarpa and Ficus cordata (Moraceae)

The aim of this study was to evaluate the antimicrobial activity of the methanol extracts from Ficus chlamydocarpa (FCR), Ficus cordata (FCB), mixture of the two plants (FCM), as well as that of the isolated flavonoids Alpinumisoflavone (2), Genistein (3), Laburnetin (4), Luteolin (5) (isolated from FCR), Catechin (7) and Epiafzelechin (8) (isolated from FCB). Mycobacteria, fungi, Gram-positive and Gram-negative bacterial species were tested for their susceptibility to the above samples. The microplate dilution and radiometric respiratory methods were used to determine the susceptibility testing of the samples against Mycobacterium smegmatis and Mycobacterium tuberculosis, respectively. The disc diffusion assay was used to determine the sensitivity of the samples, whilst the micro-dilution method was used for the determination of the minimal inhibition concentration (MIC) and the minimal microbicidal concentration (MMC) against fungi, Gram-positive and Gram-negative bacterial species. All the samples except compound 7 were found to be active to Mycobacterium smegmatis and the MIC ranged from 0.61 to 312.50microg/ml. Compound 4 showed the best activity against Mycobacterium tuberculosis exhibiting an MIC of 4.88microg/ml. The results of the diffusion test indicated that the crude extract from FCB, FCM as well as compounds 5 and 8 were able to prevent the growth of all tested (fungi, Gram-positive and Gram-negative bacteria) organisms. The inhibition effect of the crude extract from Ficus chlamydocarpa was observed on 10 (62.5%) of the 16 tested microorganisms (excluding mycobacteria) whereas that of compounds 4, 2 and 3 was respectively noted on 14 (87.5%), 8 (50.0%) and 7 (39.9%) of the tested microbial species. FCB was found to be more active than FCR on most of the tested organisms. The results provided evidence that the studied plants extract, as well as some of the isolated compounds might be potential sources of new antimicrobial drug.

Antimicrobial activity of the crude extracts and five flavonoids from the twigs of Dorstenia barteri (Moraceae).

The aim of this study was to evaluate the antimicrobial activity of the crude extract of the twigs of Dorstenia barteri (DBT) as well as that of four of the five flavonoids isolated from this extract. Gram-positive bacteria (six species), Gram-negative bacteria (12 species) and fungi (four species) were used. The agar disc diffusion test was used to determine the sensitivity of the tested samples while the well micro-dilution was used to determine the minimal inhibition concentrations (MIC) and the minimal microbicidal concentration (MMC) of the active samples. The results of the disc diffusion assay showed that DBT, isobavachalcone (1), and kanzonol C (4) prevented the growth of all the 22 tested microbial species. Other compounds showed selective activity. The inhibitory activity of the most active compounds namely compounds 1 and 4 was noted on 86.4% of the tested microorganisms and that of 4-hydroxylonchocarpin (3) was observed on 72.7%. This lowest MIC value of 19.06microg/ml was observed with the crude extract on seven microorganisms namely Citrobacter freundii, Enterobacter aerogens, Proteus mirabilis, Proteus vulgaris, Bacillus megaterium, Bacillus stearothermophilus and Candida albicans. For the tested compounds, the lowest MIC value of 0.3microg/ml (on six of the 22 organisms tested) was obtained only with compound 1, which appeared as the most active compound. This lowest MIC value (0.3microg/ml) is about 4-fold lower than that of the RA, indicating the powerful and very interesting antimicrobial potential of isobavachalcone (1). The antimicrobial activities of DBT, as well as that of compounds 1, 3, 4, amentoflavone (5) are being reported for the first time. The overall results provide promising baseline information for the potential use of the crude extracts from DBT as well as some of the isolated compounds in the treatment of bacterial and fungal infections.

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.

Antimicrobial activity of the crude extract, fractions and compounds from stem bark of Ficus ovata (Moraceae).

AIM OF THE STUDY This study was designed to investigate the antimicrobial activities of the methanol extracts from the stem bark of Ficus ovata (FOB), fractions (FOB1-6) and compounds isolated following bio-guided fractionation [3-friedelanone (1), taraxeryl acetate (2), betulinic acid (3), oleanoïc acid (4), 2-hydroxyisoprunetin (5), 6,7-(2-isopropenyl furo)-5,2,4-trihydroxyisoflavone (6), Cajanin (7) and protocatechuic acid (8)]. MATERIALS AND METHODS The micro-dilution method was used for the determination of the minimal inhibition concentration (MIC) and the minimal microbicidal concentration (MMC) against fungi (two species), gram-positive (three species) and gram-negative bacteria (five species). RESULTS The results of the MIC determinations indicated that the crude extract (FOB), fractions FOB2 and FOB4 as well as compound 5 were active on the entire studied organisms. Other samples showed selective activity, fractions FOB1, FOB3 and FOB5 being active against 50% of the tested microbial species while FOB6 was active on 40%. Compounds 8, 6, 2 and 7 prevented the growth of 80%, 70%, 50% and 20% of the organisms respectively. The lowest MIC value (156 g/ml) observed with the crude extract was recorded on Streptococcus faecalis, Candida albicans and Microsporum audouinii. The corresponding value for fractions (39 microg/ml) was noted with FOB4 against Staphylococcus aureus, while that of the tested compounds (10 microg/ml) was observed with compound 8 on Microsporum audouinii. The results of the MMC determination suggested that the cidal effect of most of the tested samples on the studied microorganisms could be expected. CONCLUSIONS The overall results provided evidence that the studied plant extract, as well as some of the isolated compounds might be potential sources of new antimicrobial drug.

Efflux pumps are involved in the defense of Gram-negative bacteria against the natural products isobavachalcone and diospyrone.

ABSTRACT The activities of two naturally occurring compounds, isobavachalcone and diospyrone, against documented strains and multidrug-resistant (MDR) Gram-negative bacterial isolates were evaluated. The results indicated that the two compounds exhibited intrinsic antibacterial activity against several Gram-negative bacteria, and their activities were significantly improved in the presence of an efflux pump inhibitor (MIC values decreased to below 10 μg/ml). In addition, the activities of isobavachalcone and diospyrone against various strains exhibiting deletions of the major efflux pump components (AcrAB, TolC) were significantly increased. The overall results indicate that isobavachalcone and diospyrone could be candidates for the development of new drugs against MDR strains and that their use in combination with efflux pump inhibitors reinforces their activity.

Synthesis of some p-toluenesulfonyl-hydrazinothiazoles and hydrazino-bis-thiazoles and their anticancer activity

A series of novel p-toluenesulfonyl-hydrazinothiazoles and hydrazino-bis-thiazoles derivatives (2a-f, 3a-f and 5-8) were synthesized by initial condensation of p-toluenesulfonylthiosemicarbazide 1 with a series of α-halogenocarbonyls in acetone or dimethylformamide (DMF)/acetone, mixture. All our synthesized compounds were submitted for further acylation reaction in the presence of acetic anhydride. The structures of newly synthesized derivatives 2a-f, 3a-f and 5-8 were confirmed by IR, (1)H-NMR, EIMS spectral data and elemental analysis. Compounds 2a, 2c, 2d, 2e and 3a showed significant anticancer activities (IC(50)<10 μM) on both prostate DU-145 and hepatocarcinoma Hep-G2 cancer cell lines.

Cytotoxicity and Mode of Action of Four Naturally Occuring Flavonoids from the Genus Dorstenia: Gancaonin Q, 4-Hydroxylonchocarpin, 6-Prenylapigenin, and 6,8-Diprenyleriodictyol

Several flavonoid-like compounds were found to possess good antiproliferative properties. Herein, we examined the ability of four naturally occuring and biologically active flavonoids from the genus Dorstenia, gancaonin Q (1), 6-prenylapigenin (2), 6,8-diprenyleriodictyol (3), and 4-hydroxylonchocarpin ( 4), to inhibit the proliferation of a panel of fourteen cancer cell lines including leukemia and solid cancer cells, as well as AML12 normal hepatocytes. The study was extended to the analysis of cell cycle distribution, apoptosis induction, and caspase 3/7 activity and the antiangiogenic properties of the four compounds. The results of the cytotoxicity assays showed that more than 50 % inhibition of proliferation was obtained with compound 1 on all the fourteen studied cancer cell lines, with IC (50) values below 20 µg/mL. Compounds 2, 4, and 3 showed selective activity, with IC (50) values below 20 µg/mL being noted on 57.15 %, 71.42 %, and 85.71 % of the fourteen cancer cell lines, respectively. None of the compounds exhibited more than 50 % inhibition against AML12 normal hepatocytes cells at 20 µg/mL. IC (50) values below or around 4 µg/mL were recorded on 28.57 % of the tested cell lines for both compound 1 and 4 and 21.43 % for compound 3, which appeared to be the best cytotoxic compounds. This study indicates that caspase 3/7 activation is one of the modes of induction of apoptosis for compounds 1, 3, and 4 in CCRF-CEM cells. The results of the antiangiogenic assay indicated that compounds 1, 3, and 4 were also able to inhibit the growth of blood capillaries on the chorioallantoic membrane of quail eggs, the best effect being noted for compound 4 (54.1 % inhibition). The results of the present work provide evidence of the cytotoxic potential of the four studied flavonoids and supportive data for further investigations.

Evaluation of flavonoids from Dorstenia barteri for their antimycobacterial, antigonorrheal and anti-reverse transcriptase activities.

The aim of this study was to evaluate the antimycobacterial, antigonorrheal and reverse transcriptase activities of five flavonoids: isobachalcone (IBC); kanzanol C (KAN); 4-hydroxylonchocarpin (4-LCP); stipulin (SPL) and amentoflavone (AMF) from Dortenia barteri, together with the crude extract from this plant. The Agar disc diffusion, broth microdilution, microplate alamar blue assay (MABA), radiometric respiratory technique using BACTEC 460 system and the reverse transcriptase (RT) assay were used for the investigations. The results of the antimycobacterial assay showed that the crude extract and compounds were able to prevent the growth of Mycobacteria with MIC<10 microg/ml being recorded with IBC on M. tuberculosis. Results of the killing rate experiment revealed that total inhibition effect on M. tuberculosis H37Rv strain was noted with IBC and SPL at day 9 when tested at 4x MIC. The results of the antigonorrheal assay indicated that MIC values below 10 microg/ml were also recorded with IBC on all the tested N. gonorrhoeae strains, meanwhile good activities (MIC<10 microg/ml) were also noted with the extract, KAN, 4-LCP and SPL on some of these strains. The anti-reverse transcriptase activities of extract and compounds also demonstrated that all samples were able to inhibit at various extents the reverse transcriptase activity, with IBC and 4-LCP showing the best effects. The overall results of this work provided evidence that the crude extract as well as some flavonoids from D. barteri could be potential sources of new antimicrobial drug against tuberculosis (TB), gonorrhea and probably the acquired immunodeficiency syndrome.

Antimicrobial activities of the methanol extract and compounds from the twigs of Dorstenia mannii (Moraceae)

BackgroundDorstenia mannii (Moraceae) is a medicinal herb used traditionally for the treatment of many diseases. In the present study, the methanol extract of D. mannii and nine of its isolated compounds, namely dorsmanin A (1), B (2), C (3), D (4), E (6), F (7), G (8) dorsmanin I (9) and 6,8-diprenyleriodictyol (5), were tested for their antimicrobial activities against yeast, Mycobacteria and Gram-negative bacteria.MethodsThe microplate alamar blue assay (MABA) and the broth microdilution method were used to determine the minimal inhibitory concentration (MIC) and minimal microbicidal concentration (MMC) of the above extract and compounds on a panel of bacterial species.ResultsThe results of the MIC determinations demonstrated that the methanol extract as well as compounds 3 and 8 were able to prevent the growth of all the fourteen studied microorganisms within the concentration range of 4 to 1024 μg/ml. The lowest MIC value for the methanol extract (64 μg/ml) was obtained on Candida albicans. The lowest value for individual compounds (4 μg/ml) was recorded with compounds 3 on Pseudomonas aeruginosa PA01 and 7 on Eschericia coli ATCC strain. The MIC values recorded with compounds 3 on P. aeruginosa PA01, 6 on C. albicans,7 on P. aeruginosa PA01 and K. pneumoniae ATCC strain and C. albicans, and 8 on P. aeruginosa PA01, PA124, P. stuartii, M. tuberculosis MTCS1 were lower than or equal to those of the reference drugs. MMC values not greater than 1024 μg/ml were recorded on all studied microorganisms with compounds 3 and 8.ConclusionThe overall results of the present investigation provided evidence that the crude extract of D. mannii as well as some of its compounds such compounds 3 and 8 could be a potential source of natural antimicrobial products.

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.