Berhanu M. Abegaz

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.

Prenylated chalcones and flavones from the leaves of dorstenia kameruniana

Abstract Two novel flavonoids : 6,7-(2,2-dimethylchromano)-5,4′-dihydroxyflavone and 3,4-,4′,5′- bis -(2,2-dimethylchromano)-2′-hydroxychalcone together with the known 6-(3-methylbut-2-enyl)apigenin and two chalcones ( E )-1-[2,4-dihydroxy-3-[3-methylbut-2-enyl]phenyl]-3-4-prop-2-en-1-one and ( E )1 - [ 2 , 4 - d i h y d r o x y - 5 - [ 3 - m e t h y l b u t - 2 - e n y l ] p h e n y l ] - 3 - [ 4 - h y d r o x y - 3 - [ 3 - m e t h y l b u t - 2 - e n y l ] p h e n y l ] - p r o p - 2 - e n - 1 - o n e were characterised from leaf tissue of Dorstenia Kameruniana . The structures were established on the basis of spectroscopic data.

Antimicrobial activity of the methanolic extract and compounds from Morus mesozygia stem bark

AIM OF THE STUDY This study was aimed at investigating the antimicrobial activity of the methanolic extract (MMB) and compounds isolated from the stem bark of Morus mesozygia, namely 3beta-acetoxyurs-12-en-11-one (1), moracin Q (2), moracin T (3), artocarpesin (4), cycloartocarpesin (5), moracin R (6), moracin U (8), moracin C (9), and moracin M (10). MATERIALS AND METHODS The liquid microdilution assay was used in the determination of the minimal inhibitory concentration (MIC) and the minimal microbicidal concentration (MMC), against nine bacterial and two fungal species. RESULTS The results of the MIC determination showed that the compounds 3, 4, 8 and 9 were able to prevent the growth of all tested microbial species. All other samples showed selective activities. Their inhibitory effects were noted on 90.9% studied organisms for the crude extract, 81.8% for compound 6, 72.7% for compound 10, 63.6% for compound 1, 54.5% for compound 5, and 45.5% for compound 2. The lowest MIC value of 39 microg/ml was obtained with the crude extract against Escherichia coli. The corresponding value for compounds (5 microg/ml) was registered with compound 9 on Shigella dysenteriae and compound 3 on E. coli, S. dysenteriae, Pseudomonas aeruginosa, Salmonella typhi and Bacillus cereus. The lowest MIC value (39 microg/ml) observed with the crude extract (on E. coli) was only eightfold greater than that of gentamycin used as reference antibiotic (RA) while the corresponding value (5 microg/ml) recorded with compounds 3 and 9 was equal to that of RA on the corresponding microorganisms. CONCLUSIONS The obtained results highlighted the interesting antimicrobial potency of M. mesozygia as well as that of the studied compounds, and provided scientific basis for the traditional use of this species.

Homoisoflavonoids and stilbenes from the bulbs of Scilla nervosa subsp. rigidifolia

Abstract Thirteen homoisoflavonoids, nine of which are new: 3-(4-methoxybenzyl)-5,7-dimethoxychroman-4-one, 3-(4-hydroxy-3-methoxybenzyl)-5-hydroxy-7-methoxychroman-4-one, 3-(4-methoxybenzylidene)-5,7-dihydroxy-6-methoxychroman-4-one, 3-(4-hydroxybenzylidene)-5-hydroxy-7-methoxychroman-4-one, 3-(4-hydroxy-3-methoxybenzyl)-5-hydroxy-6,7-dimethoxychroman-4-one, 3-(3,4-dimethoxybenzyl)-5,7-dihydroxychroman-4-one, 3-(4-methoxybenzyl)-6-hydroxy-5,7-dimethoxychroman-4-one, 3-(4-hydroxybenzyl)-5,6,7-trimethoxychroman-4-one and 3-(4-methoxybenzyl)-8-hydroxy-5,7-dimethoxychroman-4-one, were isolated from the bulbs of Scilla nervosa together with four known ones and three known stilbene derivatives. The structures of these secondary metabolites were characterized by spectroscopic means and by comparison with published information for known compounds.

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.

Doubly linked, A-type proanthocyanidin trimer and other constituents of Ixora coccinea leaves and their antioxidant and antibacterial properties

Phytochemical investigation of the ethyl acetate fraction of the methanol extract of the leaves of Ixora coccinea led to the isolation and identification of an A-type trimeric proanthocyanidin epicatechin-(2β→O→7, 4β→8)-epicatechin-(5→O→2β, 6→4β)-epicatechin named ixoratannin A-2 along with seven known compounds, epicatechin, procyanidin A2, cinnamtannin B-1, and four flavon-3-ol rhamnosides viz: kaempferol-7-O-α-L-rhamnnoside, kaempferol-3-O-α-L-rhamnoside, quercetin-3-O-α-L-rhamnopyranoside, and kaempferol-3,7-O-α-L-dirhamnoside. The structures were elucidated by the application of IR, UV, MS, 1D-, and 2D-NMR spectroscopic analyses and by comparison with literature data. Antioxidant evaluation of isolated compounds revealed that ixoratannin A-2 and cinnamtannin B-1 were the most active compounds in DPPH, inhibition of lipid peroxidation and nitric oxide radical scavenging assays. Antibacterial activities were assessed by means of agar-diffusion assays using Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus subtilis. All tested compounds inhibited the growth of B. subtilis, while only epicatechin and quercetin-3-O-α-L-rhamnopyranoside inhibited the growth of E. coli.

Diterpenoids from the stem bark of Croton zambesicus

Three clerodane diterpenoids, crotozambefurans A, B and C were isolated from the stem bark of Croton zambesicus together with the known clerodane crotocorylifuran and two trachylobanes: 7 beta-acetoxytrachyloban-18-oic acid and trachyloban-7 beta, 18-diol. Betulinol, lupeol, sitosterol and its 3 beta-glucopyranosyl derivative were also obtained. The structures of crotozambefurans A, B and C were determined, respectively, as: 15,16-epoxy-1,3,13(16),14-clerodatetraen-20,12-olide-18,19-dioic acid dimethylester, 15,16-epoxy-1,3,13(16),14-clerodatetraen-18,19,20-trioic acid trimethylester and 15,16-epoxy-3,13(16),14-clerodatrien-19,1 alpha:20,12-diolide-18-oic acid methylester, using spectroscopic analysis, especially, NMR spectra in conjunction with 2D experiments, COSY, HSQC, HMBC and TOCSY.

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.

Antitrichomonal and antioxidant activities of Dorstenia barteri and Dorstenia convexa

Dorstenia barteri and D. convexa extracts and some isolated components of the former were investigated for effectiveness against Trichomonas gallinarum and compared with quercetin and quercitrin. The antioxidant activity of the extracts/compounds was also determined. The minimum lethal concentrations (MLCs) for the extract of D. barteri leaves and twigs at 24 h were found to be 15.625 and 15.625 microg/ml, respectively. However, the MLCs of the leaf and twig extract of D. convexa were 125 and 437.5 microg/ml, respectively. The prenylated and geranylated chalcones were as active as the prenylated flavones, 6-prenylapigenin and the diprenylated derivative 6,8-diprenyleridictyol. The order of the antitrichomonal activity of the compounds at 24 h was: quercetin (0.121 microg/ml) > quercitrin (0.244 microg/ml) > or = bartericin B (0.244 microg/ml) > bartericin A (0.73 microg/ml) > stigmasterol (0.98 microg/ml) > 6,8-diprenyleridictyol = isobavachalcone = dorsmanin F (31.25 microg/ml). D. barteri extracts, quercitrin, and bartericin A, and the prenylated flavonoids had potent antioxidant properties. The twig extract of D. barteri was more potent than the leaf extract. Moderate (EC50 >50 microg/ml) and high (EC50 <50 microg/ml) antioxidant activities were detected in the leaf and twig extracts of D. barteri and the prenylated flavonoids. Prenylated flavonoids and the isolated compounds with antioxidant properties described here may account for the anti-inflammatory action of these extracts. The antitrichomonal and antioxidant activities shown by the extracts and compounds in this study are consistent with the ethnomedicinal and local use of the Dorstenia species studied.

Recent results from natural product research at the University of Botswana

Marketed plants are very important items of trade in many parts of the world. The community uses these for a variety of purposes such as foods, cosmetics, flavors, spices, and medicines. It seems that plants that are used for medicinal purposes form the most common category. Four plants used for treatment of microbial infections, viz., Bolusanthus speciosus, Erythrina latissima, Crotalaria podocarpa, and Elephantorrhiza goetzei, were investigated, and these yielded several known and novel structures, some with appreciable antibiotic activity against the test organisms. The activity of some of the isolated plants and the parts of the plant from which these were obtained lend support to their traditional use. Bulbine abyssinica and B. capitata yielded phenylanthraquinones, some of which were shown to possess strong antiplasmodial activity. In addition, these yielded isofuranonaphthoquinones, which were also found to be weakly antiplasmodial and antioxidant. Scilla nervosa yielded several known and novel homoisoflavoinds of the 3-benzylchroman-4-ones and 3-benzylidinechroman-4-one type, as well as some stilbenoids. The homoisoflavonoids showed strong antitumor activity against various cancer cell lines. Rhus pyroides gave a novel bichalcone, which showed weak antifeedant activity, consistent with the observation by farmers that the plant was avoided by corn cricket. Results from investigated Dorstenia species originating from Cameroon, Ethiopia, and Tanzania yielded styrenes, coumarins, chalcones, and flavonoids. The chalcones and flavonoids showed various levels of prenylation or geranylation, and an observation made so far is that prenylated flavonoids are only found in Dorstenia species of African origin. The only example of a bis-geranylated chalcone is found in Dorstenia.