Browsing by Author "Ishola, Anthony"

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    Characterisation, bioactivity and qsar studies of natural products from selected Namibian red marine algae
    (University of Namibia, 2020) Ishola, Anthony
    The objective of this research was to discover new drug leads from Namibian marine algae. Plocamium extracts were screened and their phytochemical contents were quantified. Both the antioxidant activity and the antimicrobial activity of the crude extracts were determined, as well as the dose-response relationship for Plocamium extracts in BALB/c mice. This was done by using acute and sub-acute toxicity parameters. In addition, the structural elucidation of the major metabolite found in the crude extract was determined and the Quantitative Structure Activity Relationships (QSARs) of the compound were determined. Methods: Frozen Plocamium leaves were soaked in dichloromethane (DCM) and methanol (MeOH) in a ratio 1:1 (v/v) for 48 hours. Concentrated Plocamium extracts were screened for phytochemical constituents. Total phenolic and flavonoid contents as well as antioxidant activity were quantified. Dried algal extracts were also reconstituted with different solvents and tested in vitro for antimicrobial activity against 12 pathogens using the Kirby Bauer disc diffusion method. Mice of known weights were infected with Escherichia coli and Pseudomonas aeruginosa by intravenous injection and sub-cutaneous methods respectively. The mice were later treated with gentamycin and ampicillin injections. Other groups of mice were treated with different concentrations of Plocamium extract over a period of five days. E. coli and P. aeruginosa loads in the faeces of the test mice were quantified daily. Plocamium extracts were purified using HPLC to fractionate the extracts. Major fractions were collected and identified by means of one and two dimensional NMR spectroscopy data and MS analysis. In terms of QSAR, the structures of the metabolites were theoretically optimized using the Merck Molecular Force Field. In addition, several physicochemical properties were computed by using the B3LYP variant of Density Functional Theory in conjunction with the 6-31G (d) basis set. Results: Plocamium cornutum and Plocamium rigidum extracted using DCM had total phenolic content of 132.85 ± 0.82 mg and 188.65 ± 0.45 mg Gallic acid equivalents per gram respectively. The IC50 values for Plocamium rigidum and Plocamium cornutum were 28.87 ± 0.82 μM and 40.11 ± 0.38 μM respectively. Ethanolic extracts of Plocamium rigidum showed a zone of inhibition of 6.35 ± 0.25 mm against Listeria monocytogenes while the standard ampicillin had no activity. From the probit plot, the LD50 was calculated to be 3556 mg/kg. A therapeutic dosage of P. rigidum of 355 mg/kg in BALB/c mice reduced E. coli load to pre-evaluation levels on the fifth day. The chemical structure of Plocamium sample I and II (Plocamium rigidum and Plocamium cornutum respectively) yielded two known compounds namely, 3,4-erythro-7-dichloromethyl-3-methyl-3,4,8-trichloro-1,5E,7E-octatriene (from sample I) and 1E,3R,4S,5E,7Z-1-bromo-3,4,8-trichloro-7-(dichloromethyl)-3-methylocta-1,5,7-triene (from sample II) respectively. CPKOvality and HLgap are physicochemical properties that best describe the variation in biological activity of the metabolites. The equation of the best fit was determined as: pIC50 = 9.91CPKovality + 0.270HL-gap-17.149 (R2 = 0.71, Adj. R2 = 0.56, R = 0.84, Std error = 0.31, and q2 = 0.55) Conclusion: DCM is a better solvent than methanol for the extraction of natural products from Plocamium species. P. rigidum showed inhibition against E. coli and L. monocytogenes in vitro. Although P. rigid inhibited the growth of E. coli, the possible development of liver lesions (in vivo) after chronic exposure is an indication of liver injury which is a sign of the chronic toxicity of P. rigidum, even at low concentrations. The probable compound responsible for this action is sample (II) above. The variables in the equation above are the parameters that best describe the variation in biological activity of the halogenated monoterpenes extracted and identified. The equation also shows that CPKovality (moderate size and shape of ligands) and a small H-L gap with high reactivity are the parameters that best optimised structure to predict improved biological activity of Plocamium metabolites.
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    The importance of nuclear magnetic resonance in elucidating the chemical structures of active components found in medicinal plants indigenous to Namibia
    (University of Namibia, 2014) Knott, Michael G.; Lates, Jennie; Ishola, Anthony
    Namibia has a vast plant biodiversity which, supported by strong Indigenous Knowledge Systems, could lead to the development of active drugs from one or more of the indigenous plants. This notification paper examines how Namibia is hampered from taking control of and developing its own natural product resources due to a lack of Nuclear Magnetic Resonance (NMR) technology.
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    The isolation, structural determination and bioactivity of 1E,3R,4S,5E,7Z-1-bromo 3,4,8-trichloro-7- (dichloromethyl)-3-methylocta-1,5,7-triene from a Namibian Plocamium species
    (University of Namibia, 2016) Knott, Michael G.; Kapewangolo, Petrina T.; Louw, Stefan; Brand, J.; Kandjengo, Lineekela; Ishola, Anthony
    A known compound namely 1E,3R,4S,5E,7Z-1-bromo-3,4,8-trichloro-7- (dichloromethyl)-3-methylocta-1,5,7-triene was isolated from a Namibian Plocamium species for the first time and characterized by means of one and two dimensional Nuclear Magnetic Resonance (NMR) spectroscopic data and Mass Spectrometry (MS) analysis. The compound exhibited minimal inhibition against HIV-1 reverse transcriptase, with a 50% inhibitory concentration of > 1000μM. However, literature reviews indicate that this compound has good cytotoxic in vitro effects.
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    Namibian marine algae as a potential source of novel bioactive natural products
    (University of Namibia, 2015) Knott, Michael G.; Ishola, Anthony
    A literature review shows that the medicinal chemistry and bioactivity of very few Namibian species has ever been investigated. In southern Africa, marine red algae such as species of Plocamium, Laurencia and Portieria are known to contain bioactive natural products. Of these three species, only Plocamium species are currently found in Namibia. In vitro testing of secondary metabolites from South African Plocamium species have demonstrated antibacterial, cytotoxic, antiplasmodial, and anti-fouling properties. Whilst the commercial benefits of some Namibian marine algae are well established, this review highlights the shortage of knowledge and research related to the pharmaceutical potential of Namibian marine algae, and how marine algae could possibly benefit the health and wellbeing of Namibians in the future.