- I am an associate professor at the University of the Western Cape Chemistry department. My specialty discipline is or... moreI am an associate professor at the University of the Western Cape Chemistry department. My specialty discipline is organic chemistry and I conduct research on the natural product chemistry of medicinal plants and selected seaweeds.edit
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Abstract A comparison is made between the molecular structures of three polysaccharides of plant origin, all of which contain alternating sequences of D -glucuronic acid and D -mannose. They vary considerably in the degree of substitution... more
Abstract A comparison is made between the molecular structures of three polysaccharides of plant origin, all of which contain alternating sequences of D -glucuronic acid and D -mannose. They vary considerably in the degree of substitution of OH groups in the core structure, O-3 of both the uronic acid and the neutral sugar being favoured. FAB-mass spectrometry showed the presence of (GlcA-Man)9 in a hydrolysis product of the least-substituted polysaccharide.
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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... more
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 an...
Research Interests: Botany, Microbiology, Plant Biology, Biology, Ecology, and 3 moreAustralian botany, Deciduous, and Bulb
ABSTRACT Dennettia tripetala a Nigerian medicinal plant widely employed in the management of oxidative stress related diseases and infections was investigated for its active constituents. A DPPH (1,1-diphenyl-2-picrylhydrazine) guided... more
ABSTRACT Dennettia tripetala a Nigerian medicinal plant widely employed in the management of oxidative stress related diseases and infections was investigated for its active constituents. A DPPH (1,1-diphenyl-2-picrylhydrazine) guided fractionation was used to target and isolate the antioxidant constituents of the ethyl acetate solvent fraction of a 20% aqueous methanol leaf extract. Two flavonoid glycosides were isolated and identified by spectral data (1H, and 13C NMR, along with ESI-TOF-MS spectrometry) as: quercetin-3-O-arabinofuranoside, avicularin (1) and vitexin-2'’-O-rhamnoside (2). In the qualitative antioxidant assay, the compounds instantly bleached the DPPH purple colour indicating free radical scavenging potential (antioxidant activity). In the micro-well dilution assay, Compound (1) was the most active with MIC values of 0.081 mg/mL against Staphylococcus aureus NCTC 6571 and 2.50 mg/mL against Escherichia coli NCTC 8196 compared to the standard drug streptomycin which had MICs of 0.039 mg/mL and 0.156 mg/mL respectively against the two organisms. None of the compounds was able to inhibit the growth of the fungi strain used at the tested concentrations. Isolation of these antioxidant and antimicrobial compounds could provide rationale for the ethnomedicinal use of this plant in traditional medicine in the management of the oxidative stress related diseases and infections.
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The global management of diabetes mellitus (DM) involves the administration of recommended anti-diabetic drugs in addition to a non-sedentary lifestyle upon diagnosis. Despite the success recorded from these synthetic drugs, the... more
The global management of diabetes mellitus (DM) involves the administration of recommended anti-diabetic drugs in addition to a non-sedentary lifestyle upon diagnosis. Despite the success recorded from these synthetic drugs, the traditional method of treatment using medicinal plants is increasingly accepted by the locals due to its low cost and the perceived no side effects. Helichrysum species are used in folk medicine and are documented for the treatment of DM in different regions of the world. This study reviews Helichrysum species and its compounds’ activities in the management of DM. An extensive literature search was carried out, utilizing several scientific databases, ethnobotanical books, theses, and dissertations. About twenty-two Helichrysum species were reported for the treatment of diabetes in different regions of the world. Among these Helichrysum species, only fifteen have been scientifically investigated for their antidiabetic activities, and twelve compounds were ide...
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Protea cynaroides (king protea) is a flowering plant that belongs to the Proteaceae family. This multi-stemmed shrub is the national flower of South Africa and has important economic and medicinal values. Traditionally, the main... more
Protea cynaroides (king protea) is a flowering plant that belongs to the Proteaceae family. This multi-stemmed shrub is the national flower of South Africa and has important economic and medicinal values. Traditionally, the main therapeutic benefits of this plant species include the treatment of cancer, bladder, and kidney ailments. There are very limited reports on the isolation of phytochemicals and their biological evaluation from P. cynaroides. In this study, the leaves of P. cynaroides were air-dried at room temperature, powdered, and extracted with 80% methanol followed by solvent fractionation (hexane, dichloromethane, ethyl acetate, and butanol). The ethyl acetate and butanol extracts were chromatographed and afforded four new (1–4) and four known (5–8) compounds, whose structures were characterized accordingly as 3,4-bis(4-hydroxybenzoyl)-1,5-anhydro-D-glucitol (1), 4-hydroxybenzoyl-1,5-anhydro-D-glucitol (2), 2-(hydroxymethyl)-4-oxo-4H-pyran-3-yl-6-O-benzoate-β-D-glucopyra...
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Research Interests: Medicinal Chemistry, Biology, Artemia, Medicinal Plants, Magnetic Resonance Spectroscopy, and 15 moreCytotoxicity, Medicine, Biological Sciences, Escherichia coli, Animals, Antimicrobial activity, Candida albicans, Aspergillus niger, CHEMICAL SCIENCES, Antibacterial activity, Bacillus subtilis, Fabaceae, Flavonols, Dimethyl Ether, and Medical and Health Sciences
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A simple and specific analytical method for the quantitative determination of flavonoids from the aerial parts of the Artemisia afra plant samples was developed. By column high-performance liquid chromatography (HPLC) with UV absorption... more
A simple and specific analytical method for the quantitative determination of flavonoids from the aerial parts of the Artemisia afra plant samples was developed. By column high-performance liquid chromatography (HPLC) with UV absorption and mass spectrometry (MS) detection, separation was achieved on a reversed-phase octadecylsilyl (C18) column with water, methanol, and acetonitrile, all containing 0.1% acetic acid, as the mobile phase. These methods were used to analyze various species of Artemisia plant samples. The wavelength used for quantification of flavonoids with the diode array detector was 335 nm. The limits of detection (LOD) by HPLC/MS were found to be 7.5, 7.5, 10, 2.0, and 2.0 ng/mL; and by LC-UV the LODs were 500, 500, 500, 300, and 300 ng/mL for apigenin, chrysoeriol, tamarixetin, acacetin, and genkwanin, respectively. The HPLC/MS method was found to be 50-150 times more sensitive than the HPLC-UV method. HPLC/MS coupled with an electrospray ionization interface is d...
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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... more
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).
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Research Interests: Plant Biology and Ecology
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Research Interests: Plant Biology and Ecology
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The leaf extract from the plant Piliostigma reticulatum was found to exhibit antimicrobial activity against somebacteriaandfungisuchasStaphylococcus aureus(NCTC6571), Escherichiacoli(NCTC10418),Bacillus subtilis (NCTC 8236), Proteus... more
The leaf extract from the plant Piliostigma reticulatum was found to exhibit antimicrobial activity against somebacteriaandfungisuchasStaphylococcus aureus(NCTC6571), Escherichiacoli(NCTC10418),Bacillus subtilis (NCTC 8236), Proteus vulgaris (NCTC 4175), Aspergillus niger (ATCC 10578) and Candida albicans (ATCC 10231). Upon investigation of the chemical constituents present in the leaf extract, a total of seven compounds were isolated and their structures were unambiguously established by spectroscopic methods including HR-MS and NMR spectrometry. Four of the isolated compounds were novel, namely 6-Cmethyl-2-p-hydroxyphenyloxychromonol (piliostigmol), 1, 6,8-di-C-methylquercetin-3,30,7-trimethyl ether, 2, 6,8-di-C-methylquercetin-3,30-dimethyl ether, 3 and 30,6,8,-tri-C-methylquercetin-3,7-dimethyl ether, 4. The other three were known C-methylated flavonols and they were isolated from P. reticulatum for the first time. These were 6-C-methylquercetin-3-methyl ether, 5, 6,8-di-C-methylkaempferol-3methyl ether, 6 and 6-C-methylquercetin-3,30,7-trimethyl ether 7. All the isolated compounds were tested for cytotoxicity using the brine shrimp toxicity assay and all of them were active albeit at different levels. With respect to antibacterial activity piliostigmol, 1 showed the highest activity against E. coli (MIC = 2.57 lg/ml, 0.006 lmol), which is three times more that of Amoxicillin, where as 4 and 7 showed the least activity.
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Abstract Leaves from Aloe ferox, divided mechanically into outer and inner layers, of which the outer formed the bulk, were extracted with organic solvents, and the residues were fractionated using in succession, water, aqueous ammonium... more
Abstract Leaves from Aloe ferox, divided mechanically into outer and inner layers, of which the outer formed the bulk, were extracted with organic solvents, and the residues were fractionated using in succession, water, aqueous ammonium oxalate, and alkalies of ...