Browsing by Author "Owusu, K.B.A."
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Item Digyalipopeptide A, an antiparasitic cyclic peptide from the Ghanaian Bacillus sp. strain DE2B(Beilstein Journal Organization Chemistry, 2023) Nartey, A.P.; Dofuor, A.K.; Owusu, K.B.A.; Camas, A.S.; Deng, H.; Jaspars, M.; Kyeremeh, K.During the continued isolation of different bacteria from highly diverse, low human activity environments in Ghana and the subsequent characterization and biological activity studies of their secondary metabolites, we found both Gram-positive and Gram-negative Bacillus strains to be ubiquitous and widespread. One of such strains, the Ghanaian novel Bacillus sp. strain DE2B was isolat ed from rhizosphere soils collected from the Digya National Park in Ghana. Chromatographic purifications of the fermented cul ture extract of the strain DE2B, led to the isolation of a cyclic lipopeptide, digyalipopeptide A (1). Using 1D and 2D NMR data, mass spectrometry sequence tagging, advanced Marfey’s analysis, and the GNPS molecular networking we solved the full structure of digyalipopeptide A (1). We found that compound 1 is a member of a somewhat homologous series of peptides produced as a mixture by the strain containing the same amino acid sequence in the cyclic peptide backbone but differing only by the length of aliphatic fatty acid side chains. When tested against Trypanosoma brucei subsp. brucei strain GUTat 3.1 and Leishmania donovani (Laveran and Mesnil) Ross (D10), digyalipopeptide A (1) gave IC50 values of 12.89 µM (suramin IC50 0.96 µM) and 4.85 µMItem Ghana’s Mangrove Wetland Endophytic Fungi: Cytotoxicity, Anti-Plasmodial and Apoptotic Activity of Quinolactacin A1/A2, Citrinadin A and Butrecitrinadin(University of Ghana, 2015-07) Owusu, K.B.A.Marine-derived endophytic fungi isolated from mangrove plants are an important and novel resource of natural bioactive compounds with their potential applications in medicine, agriculture and food industry. There are many instances that seem to suggest that, some of the novel metabolites previously isolated from certain species of marine plants and invertebrates are actually metabolites of marine-derived endophytic fungi. In this project, chemical screening of mangrove plantsConocarpus erectus, Laguncularia racemosa and Rhizophora racemosacollected along the banks of the River Butre showed that the compound 14S-bromo-1S-hydroxy-1,2,13,14-tetrahydrosphaerococenol A is not a biosynthetic product of the red alga Sphaerococcus coronopifolius but a product of possible endophytic fungi living inside the alga tissues. The compound 3-(phenethylamino)demethyl(oxy)aaptamine and its derivatives like aaptamine are not necessarily the biosynthetic products of the sea sponge Aaptos aaptos but originate from endophytic fungi within the tissues of the sponge. The mycospurine amino acid N-methylpalythine-serine originally deemed to be the metabolites of the stony coral Pocillopora eydouxicould actually be the biosynthetic products of marine-derived endophytic fungi. Mangrove plants sampled along the banks of River Butre were investigated for new or novel secondary metabolites. The HRESI/HPLC-DAD-MSn dereplication technique was employed in identifying and isolating new secondary metabolites from the mangrove plants. Out of twenty-four (24) marine-derived endophytic fungi isolated from various parts of three major mangrove plants growing in and along the banks of the River Butre in the Western Region of Ghana, six (6) different species were selected for chemical profiling, prioritization, identification and subsequent isolation of compounds. Measurement and analysis of HRESI/HPLC-DAD-MSn data of the small scale culture of these six (6) species led to the prioritization of Penicillum sp. BRS2A-AR2. Penicillum sp. BRS2A-AR2 was prioritized due to its ability to make a wide range of interesting secondary metabolites with biosynthesis prowess and ingenuity. The HRESI/HPLC-DAD-MSn analysis of Penicillum sp. BRS2A-AR2 was prioritised for further investigation because it produced metabolites which did not give any relevant hit when their masses were entered in the marine natural product based commercial database MarinLit, AntiMarin and Antibase database for novelty. The structures of these metabolites were elucidated by 1D and 2D NMR data interpretation. Quinolactacin A1/A2 was isolated with m/z of 270.1362. Citrinadin A and a new compound Butrecitrinadin were also isolated with m/z of 625.3962 and 681.4226 respectively. Citrinadin A and Butrecitrinadin were virtually identical with similar mass fragmentation pattern, eluting at the same time, having same retention time and collected together. Biological activity studies on the compounds and other compounds from the research group showed the anti-proliferative ability of the two steroidal compounds to inhibit human prostate cancer cell line with IC50 of 5.58 and 5.28 μM. Butrepyrazinone, Citrinadin Aand Butrecitrinadin showed cytotoxicity against cell lines tested. Quinolactacins isolated also showed anti-plasmodial activity with IC50 of 24.80 μM and also, showed apoptotic activity via the loss of mitochondrion membrane potential of the plasmodium parasite.Item In vitro antiprotozoan activity and mechanisms of action of selected Ghanaian medicinal plants against Trypanosoma, Leishmania, and Plasmodium parasites(Phytotherapy Research, 2018-08) Ohashi, M.; Amoa-Bosompem, M.; Kwofie, K.D.; Agyapong, J.; Adegle, R.; Sakyiamah, M.M.; Ayertey, F.; Owusu, K.B.A.; Tuffour, I.; Atchoglo, P.et.al.Trypanosomiasis, leishmaniasis, and malaria are protozoan infections of public health importance with thousands of new cases recorded annually. Control of these infection(s) with existing chemotherapy is limited by drug toxicity, lengthy parenteral treatment, affordability, and/or the emergence of resistant strains. Medicinal plants on the other hand are used in the treatment of various infectious diseases although their chemical properties are not fully evaluated. In this study, we screened 112 crude extracts from 72 selected Ghanaian medicinal plants for anti-Trypanosoma, anti-Leishmania, and anti-Plasmodium activities in vitro and investigated their mechanisms of action. Twenty-three extracts from 20 plants showed significant antiprotozoan activity against at least 1 of 3 protozoan parasites screened with IC50 values less than 20 μg/ml. Eleven extracts showed high anti-Trypanosoma activity with Bidens pilosa whole plant and Morinda lucida leaf extracts recording the highest activities. Their IC50 (selectivity index [SI]) values were 5.51 μg/ml (35.00) and 5.96 μg/ml (13.09), respectively. Nine extracts had high anti-Leishmania activity with Annona senegalensis and Cassia alata leaf extracts as the most active. Their IC50 (SI) values were 10.8 μg/ml (1.50) and 10.1 μg/ml (0.37), respectively. Six extracts had high anti-Plasmodium activity with the leaf and stem-bark extracts of Terminalia ivorensis recording the highest activity. Their IC50 (SI) values were 7.26 μg/ml (129.36) and 17.45 μg/ml (17.17), respectively. Only M. lucida at 25 μg/ml induced significant apoptosis-like cell death in Trypanosoma parasites. Anti-Leishmania active extracts induced varying morphological changes in Leishmania parasites such as multiple nuclei and/or kinetoplast, incomplete flagella division, or nuclear fragmentation. Active extracts may be potential sources for developing new chemotherapy against these infections.Item Paenidigyamycin A, Potent Antiparasitic Imidazole Alkaloid from the Ghanaian Paenibacillus sp. DE2SH(Marine Drugs, 2018-12) Osei, E.; Kwain, S.; Mawuli, G.T.; Anang, A.K.; Owusu, K.B.A.; Camas, M.; Camas, A.S.; Ohashi, M.; Alexandru-Crivac, C.N.; Deng, H.; Jaspars, M.; Kyeremeh, K.A new alkaloid paenidigyamycin A (1) was obtained from the novel Ghanaian Paenibacillus sp. isolated from the mangrove rhizosphere soils of the Pterocarpus santalinoides tree growing in the wetlands of the Digya National Park, Ghana. Compound 1 was isolated on HPLC at tR = 37.0 min and its structure determined by MS, 1D, and 2D-NMR data. When tested against L. major, 1 (IC50 0.75 µM) was just as effective as amphotericin B (IC50 0.31 µM). Against L. donovani, 1 (IC50 7.02 µM) was twenty-two times less active than amphotericin B (IC50 0.32 µM), reinforcing the unique effectiveness of 1 against L. major. For T. brucei brucei, 1 (IC50 0.78 µM) was ten times more active than the laboratory standard Coptis japonica (IC50 8.20 µM). The IC50 of 9.08 µM for 1 against P. falciparum 3d7 compared to artesunate (IC50 36 nM) was not strong, but this result suggests the possibility of using the paenidigyamycin scaffold for the development of potent antimalarial drugs. Against cercariae, 1 showed high anticercaricidal activity compared to artesunate. The minimal lethal concentration (MLC) and minimal effective concentration (MEC) of the compound were 25 and 6.25 µM, respectively, while artesunate was needed in higher quantities to produce such results. However, 1 (IC50 > 100 µM) was not active against T. mobilensis.