The ever widening level of Plasmodium falciparum resistance to antimalarials has led to the search of alternative therapies. In this context, any resources that can help alleviate the burden of the deadly malaria; including the search for new plant-derived biologically active ingredients are worthy of investigation. Amongst these, naturally occurring and synthetic chalcones have demonstrated promising potencies. In the present study, two diprenylated chalcones Bartericin A 1 and B 2, and four known natural products, stipulin 3, 4-hydroxylonchocarpin 4, isobavachalcone 5 and kanzonol B 6 were isolated from the twigs of Dorstenia barteri var. subtriangularis (Moraceae) by means of chromatographic methods. The structures of the purified compounds were elucidated by spectroscopic methods, mainly 1D and 2D-NMR spectroscopy. These compounds (1-6) were evaluated in culture against the W2 strain of P. falciparum. The evaluated compounds were found to be active in vitro against P. falciparum, 1, 3 and 4 demonstrating particular potencies with relatively low IC 50 values (2.15 µM, 5.13 µM and 3.36 µM respectively). The observed activities confirmed the chalcones as potential leads for the development of antimalarials.
The hemisynthesis of β-galactopyranosides 2, 3 and β-D-glucosaminide 4 from readily available and natural starting material, 4-hydroxylonchocarpin (1), has been achieved. 4-Hydroxylonchocarpin (1) is the major constituent of the herbaceous plant D. barteri. The synthetic pathway employed in this work involved the catalytic glycosylation of 1 under phase transfer catalysis (PTC) with different glycosyl donors under various reaction conditions. All these compounds were obtained using chromatographic methods. The structural elucidation of synthetic compounds was done by mass spectrometry and NMR analysis. The hydrogen-bonded phenolic hydroxyl group of 1 was not glycosylated under the employed conditions. A key feature of this reaction is the formation of pyran ring C in the product, β-galactopyranoside (3), and the site specific glycosylation at position C-4 of ring B. The results also confirm the isomerism equilibrium between chalcone 2 and its flavanone analog 3 which also existed in the natural sources via enzymatic reaction. This is the first report of the glycosylation of natural 4-hydroxylonchocarpin (1) using phase transfer catalysis.
Chalcones and their analogs were extracted from the twigs of Dorstenia barteri and investigated for their capacity to inhibit matrix metalloproteinase (MMP)-2 secretion from brain tumorderived U87 glioblastoma cells. Among all tested compounds, potent inhibitory activities were recorded for chalcones 1, 4, 5, and 6 and to a lesser extent for 2 and 3. Semi-synthetic derivatives 7-9 displayed low (<30%) MMP-2 secretion inhibitory activity at concentrations ranging from 0.025 to 250 µM. Chalcones 1, 4, 5, and 6 were found to be more active in comparison to the documented MMP secretion inhibitors chlorogenic acid (CHL) and epigallocatechin-3-gallate (EGCg). Hydrogenation of 1 and acid-catalyzed cyclization of 3 were performed, thus generating three semi-synthetic derivatives (7-9). The newly synthesized flavanone 7 (cycloglabrol) and its chalcone analog 8 (isocycloglabrol) exhibited low MMP-2 secretion inhibitory activity with 30% inhibition at 250 µM. The activity of Dorstenia barteri crude extracts could be attributable to the high concentration of prenylated chalcones and more specifically to stipulin 5. Altogether, the structure-activity relationships established indicated that the hydroxyl, 2,3-double bond, the prenyl group, and its positioning could account for their role in inhibiting MMP-2 secretion, a process involved in extracellular matrix degradation and brain tumor progression.
A new cerebroside 1 characterized as (2R,9Z)-2-hydroxy-N-{(1S,2S,3R,4S)-1-[(β-Dglucopyranosyloxy)methyl]-2,3,4-trihydroxyoctacosan-1-yl}-9-pentadecenamide was isolated from the stem bark of Ficus polita Vahl (Moraceae) together with four known compounds identified as sitosterol 3-O-β-D-glucopyranoside 2, betulinic acid 3, stigmasterol 4 and lupeol 5. Their structures were determined on the basis of spectroscopic methods as well as HR-ESI-MS, NMR analyses, chemical transformation, and by comparison of their physical and spectral data with those reported in the literature and with authentic specimens for some known compounds.
Objective: To assess the usefulness of Cussonia arborea in the treatment of bacterial infectious diseases.Study Design: Experimental analytical study.Place and Duration of Study: The study was done in the Laboratory of Hydrobiology and Environment of the Faculty of Sciences, University of Yaounde1; the Bacteriology Laboratory of the Yaoundé University Teaching Hospital; the Laboratory of Pharmacognosy and Pharmaceutical Chemistry of the Faculty of Medicine and Biomedical Sciences and the Laboratory of Organic Chemistry of the Faculty of Sciences of the University of Yaoundé I. The study was done in a period of six months.Methodology: The root bark of Cussonia arborea was collected in the village Yambéta (Central Region, Cameroon), dried and pulverized. Thereafter, two extractions were performed by embedding 200 g of powder in 2000 mL of 96° ethanol, and in a hydro-ethanolic mixture (30/70, v/v), respectively. Qualitative phytochemical screening was performed. Minimum inhibitory and bacterial toxicity were determined by macro-dilution in liquid medium on Staphylococcus aureus, Salmonella sp, Shigella sp and Proteus mirabilis provided by the Laboratory of Hydrobiology and Environment of the Faculty of Sciences, University of Yaounde1 and the Bacteriology Laboratory of the Yaoundé University Teaching Hospital.Results: Phytochemical screening revealed the presence of polyphenols (flavonoids, and tannins), alkaloids, quinones, saponins and, cardiac glycosides. However, coumarins were absent in the two extracts. The minimum inhibitory concentrations of the extracts ranged from 25 to 100 mg/mL, and the minimum bactericidal concentrations from 25 to 200 mg/mL. The ethanolic extract was bactericidal against Proteus mirabilis and Staphylococcus aureus, but bacteriostatic against Salmonella sp and Shigella sp. The hydro-ethanolic extract was bacteriostatic against Shigella sp and bactericidal against the other strains.Conclusion: The groups of polyphenols, alkaloids, quinones, saponins and, cardiac glycosides contained in the two extracts can justify the antibacterial activity observed against Staphylococcus aureus, Salmonella sp, Shigella sp and Proteus mirabilis.
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