Thesis (MSc (Chemistry and Biochemistry))--University of Limpopo, 2009. / Rhus leptodictya is a member of the Anacardiaceae (mango family) and is used for treating
bacteria related disease by indigenous cultures in South Africa. Domestic animals feed on the
tree during times of drought and this apparently does not cause as much tainting of milk, as
when stock feed on the related Rhus lancea. Beer is brewed from the fruits of R. leptodictya
and various parts are used in traditional medicine. The Manyika people use powdered roots of
R. leptodictya for acute pain in the chest and abdominal areas. The Xhosa people use roots for
gall sickness in cattle. A lotion of branches and smoke from burning is used for eye
complaints by Swati people.
The main aim of the study was to evaluate the antibacterial activity of extracts of the leaves
and twigs of R. leptodictya in order to confirm the traditional use and then to isolate and
characterize antibacterial compounds. To determine the best extractants for the extraction of
antibacterial compounds from the dried leaves and twigs of R. leptodictya, the efficacy of
several extractants was determined. Seven different solvents of varying polarity hexane
(Hex), chloroform (Chl), dichloromethane (DCM), ethyl acetate (Eth), acetone (Act),
methanol (Met) and water (Wat) were used in serial extraction to extract compounds from the
leaves and twigs. The mass extracted from 4g by different solvents ranged from 43-965 mg of
dry weight. The plant extracts with the highest yield was the DCM extract followed by the
methanol and acetone extracts.
Thin layer chromatography (TLC) was used to analyze the chemical composition of the
extracts using three eluent solvent systems of varying polarities i.e. CEF, BEA and EMW and
sprayed with vanillin-sulphuric acid. The chemical composition of the different extracts was
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similar with the exception of methanol and water extracts, which had only one or two visible
compounds after treating with vanillin spray reagent. Chromatograms developed in three
different solvent systems (CEF, BEA and EMW) were sprayed with 2, 2-diphenylpicrylhydrazyl
(DPPH) to evaluate antioxidant activity. There were few antioxidant
compounds present.
To evaluate the number of antibacterial compounds present in the fractions, bioautography
was used against four most important nosocomial microorganisms. S. aureus, E. faecalis, P.
aeruginosa and E. coli. Nearly all the crude serial extraction fractions contained compounds
that inhibited the growth of S. aureus. The acetone fraction had the most lines of inhibition
(6) followed by ethyl acetate (5). For quantitative evaluation of antibacterial activity,
minimum inhibitory concentration (MIC) values were determined using a serial microplate
dilution method. The MIC values for all the fractions against all the bacterial pathogens varied
from 0.04-0.63 mg/ml. The acetone extract was the most active against four bacteria with the
average MIC value of 0.36 mg/ml.
Leaves and twigs were extracted in bulk with acetone and solvent-solvent extraction was
employed which yielded seven fractions. Bioassay guided fractionation against S. aureus was
used to isolate antibacterial compounds. The largest number of antibacterial compounds
occurred in the carbon tetrachloride fraction. This fraction was subjected to silica gel column
chromatography eluting with eluents of increasing polarity. Two pure compounds were
isolated. These compounds were identified using NMR spectroscopy and mass spectroscopy,
as 2, 3 dihydro-amentoflavone and lutein. The compounds had good activity against different
bacteria with MIC values ranging from 20 to 60 μg/ml. Isolated compounds were investigated
for cytotoxicity against Vero cells with an LC50 of 9.4 μg/ml for lutein and 9.8 μg/ml for 2.3-
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dihydro amentoflavone which indicated toxicity. The much higher toxicity against
mammalian cells than again bacterial cells indicate that these compounds do not have a good
therapeutic potential but support the external use for the treatment of wounds. This is the first
report of these compounds from Rhus leptodictya. The results provide scientific support for
the use of R. leptodictya in treating bacterial infection in humans and animals.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/244 |
| Date | January 2009 |
| Creators | Sebothoma, Costar |
| Publisher | University of Limpopo (Medunsa Campus) |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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