Wilfred Mabusela

Cycloartane Glycosides from Sutherlandia frutescens

Four new cycloartane glycosides, sutherlandiosides A-D (1-4), were isolated from the South African folk medicine Sutherlandia frutescens and their structures established by spectroscopic methods and X-ray crystallography as 1 S,3 R,24S,25-tetrahydroxy-7S,10S-epoxy-9,10- seco-9,19-cyclolanost-9(11)-ene 25-O-beta-D-glucopyranoside (1), 3R,7S,24S,25-tetrahydroxycycloartan-1-one 25-O-beta-D-glucopyranoside (2), 3R,24S,25-trihydroxycycloartane-1,11-dione 25-O-beta-D-glucopyranoside (3), and 7S,24S,25-trihydroxycycloart-2-en-1-one 25-O-beta-D-glucoyranoside (4). Compound 1 represents the first secocycloartane skeleton possessing a 7,10-oxygen bridge. Compounds 2- 4 are also the first examples of naturally occurring cycloartanes with a C-1 ketone functionality. Biosynthetic considerations and chemical evidence suggest that the presence of the C-1 ketone in 2 may facilitate the ring opening of the strained cyclopropane system.

Flavonol glycosides from the south African medicinal plant Sutherlandia frutescens.

Phytochemical investigation of the leaves of Sutherlandia frutescens led to the isolation of four new 3-hydroxy-3-methylglutaroyl-containing flavonol glycosides, sutherlandins A-D ( 1- 4). Their structures were elucidated by chemical and spectroscopic methods as quercetin 3- O- beta- D-xylopyranosyl(1 --> 2)-[6- O-(3-hydroxy-3-methylglutaroyl)]- beta- D-glucopyranoside ( 1), quercetin 3- O- beta- D-apiofuranosyl(1 --> 2)-[6- O-(3-hydroxy-3-methylglutaroyl)]- beta- D-glucopyranoside ( 2), kaempferol 3- O- beta- D-xylopyranosyl(1 --> 2)-[6- O-(3-hydroxy-3-methylglutaroyl)]- beta- D-glucopyranoside ( 3), and kaempferol 3- O- beta- D-apiofuranosyl(1 --> 2)-[6- O-(3-hydroxy-3-methylglutaroyl)]- beta- D-glucopyranoside ( 4).

Quantitative determination of flavonoids and cycloartanol glycosides from aerial parts of Sutherlandia frutescens (L.) R. BR. by using LC-UV/ELSD methods and confirmation by using LC-MS method.

This paper describes the first analytical method for the determination of four flavonoids (sutherlandins A-D) and four cycloartanol glycosides (sutherlandiosides A-D) from the aerial parts of Sutherlandia frutescens (L.) R. Br. A separation by HPLC was achieved by using a reversed phase (RP-18) column, PDA with ELS detection, and a water/acetonitrile gradient as the mobile phase. The wavelength used for quantification of four flavonoids with the diode array detector was 260 nm. Owing to their low UV absorption, the cycloartanol glycosides were detected by evaporative light scattering. The method was validated for linearity, repeatability, limits of detection (LOD) and limits of quantification (LOQ). The limits of detection and limits of quantification of eight compounds were found to be in the range from 0.1 to 7.5 microg/mL and 0.5 to 25 microg/mL, respectively. The analysis of products showed considerable variation of 1.099-5.224 mg/average weight for the major compound, sutherlandioside B. The eight compounds in plant sample and products of S. frutescens were further confirmed by LC-ESI-TOF. This method involved the use of the [M+H](+) and [M+Na](+) ions in the positive ion mode with extractive ion monitoring (EIM).

An assessment of two Carpobrotus species extracts as potential antimicrobial agents

For centuries, indigenous people in South Africa have used a variety of medicinal herbs to treat chronic infections. This investigation focused on two Carpobrotus species belonging to the family, Aizoaceae, in an attempt to assess their antimicrobial potential. Extracts of varying polarities of the plants were prepared and tested against Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans and Mycobacterium smegmatis. For the disc diffusion method, Ciprofloxacin (40 microg/disc) served as positive control for S. aureus, P. aeruginosa and M. smegmatis, whereas amphotericin B (25 microg/disc) was the control for C. albicans. A sample concentration of 10 mg/ml was used. Minimum inhibitory concentrations (MIC) were determined by two-fold serial dilution. Phytochemical analysis was completed to test for the presence of flavonoids, hydrolysable tannins, phytosterols and aromatic acids. The ethyl acetate extracts (21 microl of 95 mg/ml) were used for bio-autography, together with TLC analyses. Carpobrotus muirii and Carpobrotus quadrifidus showed antimicrobial activity against S. aureus and M. smegmatis in the disc diffusion method and inhibition against S. aureus and M. smegmatis was observed by clear zones on the TLC plate. This investigation confirms that extracts of these Carpobrotus species that are used as indigenous medicines, exhibit anti-bacterial activity. This scientific information can serve as an important platform for the development of inexpensive, safe and effective natural anti-infective medicines.

Efficacy of Artemisia afra phytotherapy in experimental tuberculosis.

Artemisia afra [Jacq] (Asteraceae) phytotherapy is widely used for its medicinal properties in traditional practices. In this study we investigated whether extracts of A. afra are capable of controlling mycobacterial replication. For Mycobacterium aurum cultured in the presence of aqueous-, methanol- and dichloromethane (DCM) extracts of A. afra we found that bacterial replication was inhibited by the dichloromethane extract only. Activity of the DCM extract was confirmed in dose-dependent studies against both M. aurum and M. tuberculosis with an IC(50) =270 microg/ml and IC(50) = 290microg/ml, respectively. Fractionation of the DCM extract and evaluation of its efficacy in vitro found that most of the antimycobacterial activity was associated with isolate fraction C8 that contained several sesquiterpene lactones, the most prominent of which are Artemin and Arsubin. Evaluation of the bactericidal efficacy in vitro showed that isolate fraction C8 reduced replication of M. aurum and M. tuberculosis in a dose-dependent manner with IC(50) =1.9 microg/ml and IC(50) = 2.0 microg/ml, respectively, and an MIC = 10 microg/ml. Further, isolate fraction C8 and the DCM extract was administered to M. tuberculosis-infected mice at a tolerated dose of 1000 microg/kg for up to 26 weeks and mycobacterial burdens compared to untreated-, INH/RIF treated- and aqueous-extract-treated animals to assess its bactericidal activity in vivo. Bacterial replication remained unaffected during treatment with either isolate fraction C8 or the DCM extract resulting in pulmonary and splenic bacilli burdens comparable to that of untreated mice. In contrast, INH/RIF treatment cleared M. tuberculosis infection after only 8 weeks to undetectable levels. Interestingly, treatment of M. tuberculosis-infected mice with aqueous extract of A. afra regulated pulmonary inflammation during early infection notwithstanding its inability to inhibit mycobacterial growth. This study clearly demonstrates that A. afra contains in vitro anti-mycobacterial activity, modulates pulmonary inflammation in early mycobacterial infection, and that the mouse experimental tuberculosis model may serve as a useful assay for evaluating the utility of phytotherapy.

Antioxidant Radical Scavenging Properties of Phenolic Pent-4-En-1-Yne Derivatives Isolated From Hypoxis Rooperi. A DFT Study in vacuo and in Solution

B3LYP/6-311+G* calculations were performed on five phenolic pent-4-en-1-yne derivatives, namely rooperol, dehydroxyrooperol I and II, bis-dehydroxyrooperol, and hypoxoside, to investigate and compare their antioxidant radical scavenging properties. The main objectives were to model, for the first time, the antioxidant properties of dehydroxyrooperol I and II and bis-dehydroxyrooperol, to clarify the possible role of hypoxoside as radical scavenger and to provide insight into molecular geometry factors influencing the radical scavenging properties of phenolic pent-4-en-1-yne derivatives. The study was conducted by checking the molecules’ ability for two main antiradical mechanisms, hydrogen atom transfer and electron transfer. The results indicated that the antiradical properties of rooperol and the two dehydroxyrooperols are predominantly exerted through the hydrogen atom transfer mechanism and are the outcome of the stabilization of their neutral radical species through the interplay of hydrogen bond(s) and spin density distributions stabilizing their neutral radical species. The antiradical properties of bis-dehydroxyrooperol may be explained only in terms of the spin density distribution of its neutral radical species. The antiradical properties of hypoxoside, with O−H bond dissociation enthalpy considerably greater than that of phenol, could be considered to be minor and mainly governed by electron transfer mechanism.

The carbon and nitrogen cost associated with the growth, reproductive and dormant phases of two South African semi-arid geophytic species of Gethyllis (Amaryllidaceae)

Gethyllis multifolia L.Bolus and G. villosa Thunb. (Family: Amaryllidaceae) are deciduous and bulbous geophytes that occur in the succulent Karoo biome of South Africa. Both species occupy the same natural habitat, but G. multifolia is threatened and G. villosa not. Both G. multifolia and G. villosa require seasonal bulb reserves for initial vegetative and reproductive growth. In spite of G. villosa having smaller bulbs than G. multifolia, both species produce similar flower sizes and weights. The aim of the present study was to determine the carbon and nitrogen costs of vegetative and reproductive growth during the phases of growth, senescence, reproduction and dormancy of these bulbous species. The rates, costs and efficiencies of biomass production during various growth phases of the two species were determined in a comparative experiment. The results show that in spite of a significantly smaller bulb, G. villosa produced more leaves per unit bulb mass and invested more carbon and nitrogen resources into the bulbs during senescence. G. villosa also had a higher flower production, relative to bulb weight, than did G. multifolia. These physiological responses suggest that G. villosa may be more efficient at carbon and nitrogen resource utilisation.

Polysaccharides from the South African medicinal plant Artemisia afra: Structure and activity studies

Artemisia afra (Jacq. Ex. Willd), is an indigenous plant in South Africa and other parts of the African continent, where it is used as traditional medicine mostly for respiratory conditions. The objective of this study was to investigate the structural features of the polysaccharides from the leaves of this plant, as well as the biological activities of the polysaccharide fractions against the complement assay. Leaves of Artemisia afra were extracted sequentially with organic solvents (dichloromethane and methanol), 50% aqueous ethanol, and water at 50 and 100°C respectively. The polysaccharide extracts were fractionated by ion exchange chromatography and the resulting fractions were tested for biological activity against the complement fixation assay. Active fractions were further fractionated using gel filtration. Monosaccharide compositions and linkage analyses were determined for the relevant fractions. Polysaccharides were shown to be of the pectin type, and largely contain arabinogalactan, rhamnogalacturonan and homogalacturonan structural features. The presence of arabinogalactan type II features as suggested by methylation analysis was further confirmed by the ready precipitation of the relevant polysaccharides with the Yariv reagent. An unusual feature of some of these polysaccharides was the presence of relatively high levels of xylose as one of its monosaccharide constituents. Purified polysaccharide fractions were shown to possess higher biological activity than the selected standard in the complement assay. Digestion of these polysaccharides with an endo-polygalacturonase enzyme resulted in polymers with lower molecular weights as expected, but still with biological activity which exceeded that of the standard. Thus on the basis of these studies it may be suggested that immunomodulating properties probably contribute significantly to the health-promoting effects of this medicinal plant.