Pantaleon Ambassa

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.

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.

Synthesis and Evaluation of Anticancer Activity of O-allylchalconeDerivatives

A large number of novel O -allylchalcones were synthesized by Claisen Schmidt condensation reaction of O -allylvanillin 3 with appropriate substituted acetophenones 4a-h. These model chalcones 5a-h and their precursor O -allylvanillin were screened for their in vitro cytotoxicactivity against four human cancer cell lines. The most potent compound in this series with the IC 50 values below or around 10 μM were 5f against THP-1 cells (10.42 μM) and 5g against THP-1 (4.76 μM), DU-145 (5.21 μM), HL60 (7.90 μM), Hep-G2 (10.12 μM) and MCF-7 (10.32 μM).

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.