Steroids and terpenoids from the bark and the wood of <i>Entandrophragma Cylindricum</i>

Bull. Chem. Soc. Ethiop. 1994, 8(1) 15-20

Steroids and terpenoids from the bark and the wood of Entandrophragma Cylindricum

Bull. Chem. Soc. Ethiop. 1994, 8(1) 15-20

Antibacterial and antioxidant activities of extracts and some flavonoids from the leaves of Clerodendrum buchholzii Gurke (Verbenaceae)

Morbidity and mortality due to diarrhoea continues to be a major problem in many developing countries. The most common microorganisms responsible for diarrhoeal diseases are Vibrio cholerae, Escherichia coli and Shigella spp. The present study aims to evaluate the antibacterial and antioxidant activities of extracts and compounds from the leaves of Clerodendrum buchholzii, a plant traditionally used in the African pharmacopeia for the treatment of furunculosis, echymosis and gastritis. The dried leaves were macerated in methanol (MeOH) to afford the crude extract that was extracted with ethyl acetate (EtOAc) and n-butanol (n-BuOH) to obtain EtOAc and n-BuOH extracts, respectively. The column chromatography of EtOAc and n-BuOH extracts followed by purification of different fractions led to the isolation of four known flavonoids [acacetin 7-O-β-D-glucoside (1), kaempferol 7-O-β-D-glucoside (2), acacetin (3) and apigenin (4)]. Structures of isolated compounds were assigned on the basis of spectroscopic analysis, and by comparison of our data with those of the literature. The antioxidant activity was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) and gallic acid equivalent antioxidant capacity (GEAC) assays. The antibacterial activity was assessed using broth microdilution method by performing minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) against the strains of Gram-positive bacterium, Staphylococcus aureus (a major cause of community and hospital-associated infection), and Gram-negative multi-drug resistant bacteria, Vibrio cholerae (causative agent of cholera) and Shigella flexneri (causative agent of shigellosis). All of the extracts showed different degrees of antioxidant and antibacterial activities. Apigenin (4) obtained from EtOAc extract displayed the largest antibacterial and antioxidant properties which were in some cases equal or higher than those of reference drugs. Our results showed that C. buchholzii has potentials as a natural source of anti-diarrhoeal and free radical scavenging products, and could be given further investigations.Keywords: Clerodendrum buchhlzii, Verbenaceae, Flavonoids, Antibacterial, Antioxidan

Antimicrobial activities of flavonoid glycosides from Graptophyllum grandulosum and their mechanism of antibacterial action

Abstract Background The search for new antimicrobials should take into account drug resistance phenomenon. Medicinal plants are known as sources of potent antimicrobial compounds including flavonoids. The objective of this investigation was to evaluate the antimicrobial activities of flavonoid glycosides from Graptophyllum grandulosum, as well as to determine their mechanism of antibacterial action using lysis, leakage and osmotic stress assays. Methods The plant extracts were prepared by maceration in organic solvents. Column chromatography of the n-butanol extract followed by purification of different fractions led to the isolation of five flavonoid glycosides. The antimicrobial activities of extracts/compounds were evaluated using the broth microdilution method. The bacteriolytic activity was evaluated using the time-kill kinetic method. The effect of extracts on the red blood cells and bacterial cell membrane was determined by spectrophotometric methods. Results Chrysoeriol-7-O-β-D-xyloside (1), luteolin-7-O-β-D-apiofuranosyl-(1 → 2)-β-D-xylopyranoside (2), chrysoeriol-7-O-β-D-apiofuranosyl-(1 → 2)-β-D-xylopyranoside (3), chrysoeriol-7-O-α-L-rhamnopyranosyl-(1 → 6)-β-D-(4"-hydrogeno sulfate) glucopyranoside (4) and isorhamnetin-3-O-α-L-rhamnopyranosyl-(1 → 6)-β-D-glucopyranoside (5) were isolated from G. grandulosum and showed different degrees of antimicrobial activities. Their antibacterial activities against multi-drug-resistant Vibrio cholerae strains were in some cases equal to, or higher than those of ciprofloxacin used as reference antibiotic. The antibacterial activities of flavonoid glycosides and chloramphenicol increased under osmotic stress (5% NaCl) whereas that of vancomycin decreased under this condition. V. cholerae suspension treated with flavonoid glycosides, showed a significant increase in the optical density at 260 nm, suggesting that nucleic acids were lost through a damaged cytoplasmic membrane. A decrease in the optical density of V. cholerae NB2 suspension treated with the isolated compounds was observed, indicating the lysis of bacterial cells. The tested samples were non-toxic to normal cells highlighting their good selectivity index. Conclusions The results of the present study indicate that the purified flavonoids from G. glandulosum possess antimicrobial activities. Their mode of antibacterial activity is due to cell lysis and disruption of the cytoplasmic membrane upon membrane permeability

Antimicrobial activities of saponins from Melanthera elliptica and their synergistic effects with antibiotics against pathogenic phenotypes

Abstract Background Resistance of bacteria and fungi to antibiotics is one of the biggest problems that faces public health. The present work was designated to evaluate the antimicrobial activities of saponins from Melanthera elliptica and their synergistic effects with standard antibiotics against pathogenic phenotypes. The plant extract was prepared by maceration in methanol. The methanol extract was partitioned into ethyl acetate and n-butanol extracts. Column chromatography of the n-butanol extract followed by purification of different fractions led to the isolation of four saponins. Their structures were elucidated on the basis of spectra analysis, and by comparison with those from the literature. The antimicrobial activities of the extracts/compounds alone and their combinations with tetracycline and fluconazole were evaluated using the broth microdilution method through the determination of minimum inhibitory concentration (MIC) and minimum microbicidal concentration. Results Four compounds: 3-O-β-d-glucuronopyranosyl-oleanolic acid (1), 3-O-β-d-glucuronopyranosyloleanolic acid 28-O-β-d-glucopyranosyl ester (2), 3-O-β-d-glucopyranosyl(1 → 2)-β-d-glucuronopyranosyl oleanolic acid (3) and 3-O-β-d-glucopyranosyl(1 → 2)-β-d-glucuronopyranosyl oleanolic acid 28-O-β-d-glucopyranosyl ester (4) were isolated. Compounds 1, 2 and 3 showed the largest antibacterial activities (MIC = 8–128 μg/mL) whereas compound 4 displayed the highest antifungal activities (MIC = 8–16 μg/mL). The antibacterial activities of compounds 1 and 2 (MIC = 16–32 μg/mL) against multi-drug-resistant Escherichia coli S2 (1) and Shigella flexneri SDINT are equal to those of vancomycin (MIC = 16–32 μg/mL) used as reference antibiotic. Conclusions The present study showed significant antimicrobial activity of compounds 1, 2, 3 and 4 against the tested microorganisms. The saponins act in synergy with the tested standard antibiotics. This synergy could lead to new options for the treatment of infectious diseases and emerging drug resistance

Urea derivatives from Pentadiplandra brazzeana

Four urea derivatives were isolated from the roots of Pentadiplandra brazzeana, and their structures were elucidated by spectroscopic techniques. N-Benzyl-N'-(4-methoxybenzyl)urea (1) is a new compound, although N,N'-di-(4- methoxybenzyl)urea (2), N,N'-dibenzylurea (3), and p-methoxythiobenzaldehyde (4) are reported from a natural source for the first time

New friedelane triterpenes from Lepidobotrys staudtii

Three new dihydroxy-3-friedelanone triterpenes were isolated from the leaves and the stem bark of the Cameroonian medicinal plant Lepidobotrys staudtii. Structure elucidation by spectroscopic techniques showed that they are 2α,29-dihydroxy-3-friedelanone (1a), 2β,21α-dihydroxy-3-friedelanone (2a) and 6β,21α-dihydroxy-3-friedelanone (3). In addition, the known monohydroxy-3-friedelanones 4, 5, 6 and 7 were obtained

Geranylated flavonoids from Dorstenia poinsettifolia

Two new geranylated flavonoids, poinsettifolins A and B, were isolated from the extracts of the herb Dorstenia poinsettifolia, and the structures were determined with NMR spectroscopy and mass spectrometry. In addition, the flavone 5,7,4-trihydroxy-8-prenylflavone (licoflavone C), the chalcones 4,2',4'-trihydroxy-3'-prenylchalcone (isobavachalcone) and isobavachromene, the triterpene butyrospermol, and the carotenoid lutein were isolated