Browsing by Author "Nyambe, Moola M."
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Item Anti-gonococcal activity of extracts from selected Namibian medicinal plants and computational studies of xerantholide, a neisseria gonorrhoeae inhibitor(University of Namibia, 2023) Nyambe, Moola M.Neisseria gonorrhoeae, the causative agent of a sexually transmitted infection, gonorrhea, has developed resistance to all available antibiotics. It is found in humans only and if left untreated can lead to serious complications such as infertility and disseminated gonococcal infections. The search for new effective, affordable, and readily accessible drugs for the treatment of gonorrhea thus continues. Plants have been a good source of structurally diverse lead compounds from which drugs have been developed. Various communities in Namibia commonly use plants in traditional health care for the treatment of sexually transmitted infections (STIs). However, these plants have not yet been evaluated for their anti-gonococcal activity and human safety. Therefore, this study aimed to isolate compounds from plants that are traditionally used to treat gonorrhea, ascertain their anti-gonococcal activity, and elucidate the structures of these compounds in an effort towards searching for selective anti-gonococcal agents. Another aim was to employ computational approaches, including density functional theory (DFT), molecular docking, prediction of activity spectra for substances (PASS) and Quantitative Structure-Property Relationship (QSPR), to model the interaction of xerantholide and its analogues with the active site of Neisseria gonorrhoeae carbonic anhydrase (NgCA) and to investigate the geometry, electronic structure, and biological activity spectra. Agar well diffusion and broth microdilution methods were used to determine the minimum inhibitory concentration (MIC) of extracts. Isolation and characterization of compounds were done using thin layer chromatography (TLC), column chromatography, x-ray diffraction and nuclear magnetic resonance (NMR). Crude extracts from six plants were ii confirmed to have anti-gonococcal activity (MIC 2.5-5.0 mg/mL). Xerantholide, with an MIC50 = 0.095 mg/mL was isolated from Pechuel-loeschea leubnitziae leaves. Molecular docking analysis revealed that xerantholide and its analogues docked with binding affinities ranging from -5.3 to -7.4 kcal/mol and DFT predicted binding energy of -16.5 to – 43.1 kcal/mol for these sesquiterpene lactones. Based on the docking results, binding of these compounds to NgCA involves hydrogen bonding, ligand-metal-acceptor, and hydrophobic interactions. Using QSPR, a six descriptors model with good predictive ability (R = 0.789, R 2 = 0.623, AdjR2 = 0.578, BIC = 241, AIC = 225) was developed. Finally, a PASS analysis showed that these compounds are potential antibacterial agents. The results in this study suggest that the studied sesquiterpene lactones offer potential anti-gonococcal and inhibitory activity towards NgCA, thus further in-vitro studies are recommended.Item An efficient method for the synthesis of dihydropyridine by hantzsch reaction with Fe/SiO2 nano heterogeneous catalysts(2020) Rahman, Ateeq; Nehemia, P.N.; Nyambe, Moola M.An efficient method for the synthesis of dihydropyridines (DHPs) by Hantzsch reaction with Fe/SiO2 heterogeneous catalysts was developed. The Fe/SiO2 catalysts was prepared by impregnation method. The catalysts were characterized by IR and SEM instruments. The SEM results indicated that Fe/SiO2 nano spheres were formed. The reaction procedure involved reaction of aldehyde, ethyl acetoacetate (EAA), ammonium acetate (NH4OAc) and ethanol under reflux. The study was focused on optimizing reactions conditions: Standardization of catalyst, substrate of study and solvent study. In order to iden-tify the best active catalysts, five different ratios of catalyst were synthesized and evaluated for the ti-tle reaction under similar conditions. To standardize the active catalysts, different temperature condi-tions (i.e. room temperature, 60 ºC and 80 ºC) as well as catalysts amounts were evaluated. Under these established conditions, 2.5% Fe/SiO2 was the best active catalysts that resulted. Benzaldehyde and p-anisaldehyde were used to study the effect of having various substrates on the conversion and reaction time, especially the substituted aldehydes. The best results were obtained by reacting p-anisaldehyde with EAA, NH4OAc, and ethanol at 60 ºC with 0.3 grams of 2.5% Fe/SiO2 heterogeneous catalysts. Thin Layer Chromatography (TLC) monitoring of the reaction mixture showed no selectivity at high temperatures (80 ºC) with 15% Fe/SiO2. Standardization of solvent study was executed with two solvents, ethanol and acetonitrile. The product dihydropyridines were analyzed using gas chroma-tography-mass spectrometry (GC-MS). The melting points of the products were compared with authen-tic samples reported in the literature. Hence, the Fe/SiO2 catalysts is eco-friendly and economically de-veloped for the title reaction.Item Nutritional and anti-nutritional composition of Diospyros mespiliformis and Hyphaene petersiana fruits from Namibia(University of Namibia, 2019) Nyambe, Moola M.; Hakwenye, Hilaria; Benyamen, M.S.Wild fruits play an important role in the well-being of many people in Namibia. Two wild fruits namely, Diospyros mespiliformis Hochst. ex A. DC (Ebenaceae) and Hyphaene petersiana Klotzsch ex Mart. (Arecaceae) were analyzed for proximate, nutritional and anti-nutritional composition. The proximate results showed that the moisture content ranged between 8.3-12%, crude fat (0.1-0.45 mg/g), crude protein (1.6-2.6 mg/g), carbohydrate (4-5.3 mg/g), and ash content (3.3-6 mg/g). The mineral contents of the studied fruits were: calcium (5.01-20.33 mg/kg), potassium (94.8-245.94 mg/kg) and sodium (2.80-11.65 mg/kg). Trace elements such as iron (0.14-2.44 mg/kg) and zinc (0.17-0.19 mg/kg) were also detected. Anti-nutrient values were lower than those for established toxic values. High levels of saponins (2.46 mg/g), tannins (0.10 mg/g) and phytate (0.12 mg/g) were detected in H. petersiana pulp, and oxalate (0.04 mg/g) was detected in D. mespiliformis pulp. However, these anti-nutritional factors were within established safe consumption limits. The results of this study signify that the two fruits have high concentrations of essential minerals and low anti-nutrients; thus their consumption is recommended, especially in poor settings.