Browsing by Author "Beukes, Denzil R."

Now showing 1 - 7 of 7
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    Balancing yields and sustainability: an eco-friendly approach to losartan synthesis using green palladium nanoparticles
    (Multidisciplinary Digital Publishing Institute (MDPI), 2025) Antunes, Edith M.; Adegoke, Yusuf Adeyemi; Mgwigwi, Sinazo; Malan, Sarel F.; Beukes, Denzil R.
    This study presents a sustainable, environmentally friendly synthetic route for the production of key intermediates in losartan using palladium nanoparticles (PdNPs) derived from a brown seaweed, Sargassum incisifolium, as a recyclable nanocatalyst. A key intermediate, biaryl, was synthesized with an excellent yield (98%) via Suzuki–Miyaura coupling between 2-bromobenzonitrile and 4-methylphenylboronic acid, catalyzed using bio-derived PdNPs under mild conditions. Subsequent bromination using N-bromosuccinimide (NBS) under LED light, followed by imidazole coupling and tetrazole ring formation, allowed for the production of losartan with an overall yield of 27%. The PdNP catalyst exhibited high stability and recyclability, as well as strong catalytic activity, even at lower loadings, and nitrosamine formation was not detected. While the overall yield was lower than that of traditional industrial methods, this was due to the deliberate avoidance of the use of toxic reagents, hazardous solvents, and protection/deprotection steps commonly used in conventional routes. This trade-off marks a shift in pharmaceutical process development, where environmental and safety considerations are increasingly prioritized in line with green chemistry and regulatory frameworks. This study provides a foundation for green scaling up strategies, incorporating sustainability principles into drug synthesis.
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    Bioassay guided fractionation of Angiotensin converting enzyme inhibitor compound from Hypericum perforatum
    (University of the Western Cape, 2019) Mokwelu, Onyinye Vivian; Obikeze, Kenechukwu; Beukes, Denzil R.
    Due to the contribution of hypertension to various cardiovascular diseases, many studies are currently focused on identifying efficient bioactive compounds with antihypertensive activity and thus reducing the levels of cardiovascular disease. ACE inhibitors are an important component of the therapeutic regimen for treating hypertension, but due to the increase in the prevalence of side effects of synthetic compounds, alternative and complementary medicines which may consist of pure bioactive compound or a combination of various compounds from natural sources are gaining importance in overcoming hypertension. Hypericum perforatum has been studied for various activities including anti-bacterial, anti-depressant, anti-oxidant properties, but studies on its cardiovascular effects specifically ACE inhibitory activity have not yet been explored. In this study, ACEI assay-guided fractionation of the ethanol extract of Hypericum perforatum was carried out other to isolate a compound with ACE inhibition. A compound – (3-hydroxy 4, 4 dimethyl-4-butyrolactone) was isolated from an active fraction of the plant extract and was tested for ACE inhibition and its chemical structure elucidated using 1HNMR and C13NMR spectrometry and further characterized using mass spectrometry and FTIR.
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    Design and synthesis of new scaffolds as antiproliferative agents and potential hsp90 inhibitors
    (University of Western Cape, 2020) Adegoke, Yusuf Adeyemi; Beukes, Denzil R.
    Natural products have been an important source of drugs and novel lead compounds in drug discovery. Their unique scaffolds have led to the synthesis of derivatives that continue to give rise to medicinally relevant agents. Thus, natural product-inspired drugs represent a significant proportion of drugs in the market and with several more in development. Cancer is among the leading public health problems and a prominent cause of death globally. Chemotherapy has been important in the management of this disease even though side effects that arise due to lack of selectivity is still an issue.
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    Hyphenated LC-ICP-MS/ESI-MS identification of halogenated metabolites in South African marine ascidian extracts
    (The South African Chemical Institute, 2018) Bromley, Candice L.; Raab, Andrea; Parker-Nance, Shirley; Beukes, Denzil R.; Jaspars, Marcel; Davies-Coleman, Michael T.
    Extracts of 13 species of marine ascidian collected in Algoa Bay were analyzed by LC-ICP-MS/ESI-MS. This technique allows parallel analysis of the molecular species and the presence of certain elements. The LC-ICP-MS/ESI-MS technique was used to target iodinated metabolites in this study. Three ascidian species afforded the known 3,5–diiodo-4-methoxyphenethylamine (12), which was confirmedby the isolation of this metabolite fromAplidium monile.MS also suggested the presence of theknown 3,5–dibromo-4-methoxyphenethylamine (10) and the new 3-bromo-5–iodo-4-methoxyphenethylamine (11) in the A. monile extract. The presence of the known 3,5-dibromotetramethyltyrosine (21) and the new 3-iodotetramethyltyrosine (23) in extracts of an unidentified Didemnum species was similarly proposed from MS evidence. This is the first report of the occurrence of iodinated metabolites in South African marine invertebrates.
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    Novel South African rare actinomycete kribbella speibonae Strain SK5: A prolific producer of hydroxamate siderophores including new dehydroxylated congeners
    (MDPI, 2020) Beukes, Denzil R.; Warner, Digby F.; Jaspars, Marcel
    In this paper, we report on the chemistry of the rare South African Actinomycete Kribbella speibonae strain SK5, a prolific producer of hydroxamate siderophores and their congeners. Two new analogues, dehydroxylated desferrioxamines, speibonoxamine 1 and desoxy-desferrioxamine D1 2, have been isolated, together with four known hydroxamates, desferrioxamine D1 3, desferrioxamine B 4, desoxy-nocardamine 5 and nocardamine 6, and a diketopiperazine (DKP) 7. The structures of 1–7 were characterized by the analysis of HRESIMS and 1D and 2D NMR data, as well as by comparison with the relevant literature.
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    Sutherlandiosides e−k: further cycloartane glycosides from sutherlandia frutescens
    (Elsevier Ltd, 2024) Tchegnitegni, Billy Toussie; Lerata, Mookho S.; Beukes, Denzil R.; Antunes, Edith M.
    A further chemical investigation of the butanol extract of leaves from the South African medicinal plant Sutherlandia frutescens led to the isolation of eight previously unreported saponins (1−8), together with the known sutherlandio sides A−D. Their structures were established by spectroscopic (1D and 2D NMR) analyses, CD, optical rotation, mass spectrometry, as well as chemical conversions. The isolates were screened for their cytotoxic activity against the MCF-7 human breast cancer cell line, although no significant activity was observed. In addition to the chemophenetic markers for this genus, i.e. the cycloartane glycosides, the present work also reports on the first isolation of an oleanan-type saponin from the Sutherlandia genus, forming an important fingerprint for the chemical composition of the plant.
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    Sutherlandiosides E−K: Further cycloartane glycosides from Sutherlandia frutescens
    (Elsevier Ltd, 2024) Tchegnitegni, Billy Toussie; Lerata, Mookho S.; Beukes, Denzil R.; Antunes, Edith M.
    A further chemical investigation of the butanol extract of leaves from the South African medicinal plant Sutherlandia frutescens led to the isolation of eight previously unreported saponins (1−8), together with the known sutherlandiosides A−D. Their structures were established by spectroscopic (1D and 2D NMR) analyses, CD, optical rotation, mass spectrometry, as well as chemical conversions. The isolates were screened for their cytotoxic activity against the MCF-7 human breast cancer cell line, although no significant activity was observed. In addition to the chemophenetic markers for this genus, i.e. the cycloartane glycosides, the present work also reports on the first isolation of an oleanan-type saponin from the Sutherlandia genus, forming an important fingerprint for the chemical composition of the plant.