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University of Namibia (2017)

Characterisation of major metabolites of wild everlasting, Helichrysum Argyrosphaerum

Namate, Taonga Moffat

Titre : Characterisation of major metabolites of wild everlasting, Helichrysum Argyrosphaerum

Auteur : Namate, Taonga Moffat

Université de soutenance  : University of Namibia

Grade : Master of Science (MS) (Chemistry) 2017

Résumé
Plant species in the genus Helichrysum, are widely used in Southern African traditional medicine. Antibacterial and antifungal activities were reported for most of the Helichrysum species including H. argyrosphaerum. As a starting point to elucidate the structures of the compounds that may be responsible for these properties, phytochemical screening was performed to qualitatively identify the classes of compounds present. The results showed that the plant is rich in polyphenols and flavonoids, specifically flavones. This study employed a screening approach combining high pressure liquid chromatography – ultraviolet spectroscopy – high resolution tandem mass spectrometry (HPLC-UV-HRMS/MS) to elucidate the chemical structures of the major compounds of H. argyrosphaerum. First, suitable reversed phase liquid chromatography (RPLC) and hydrophilic interaction liquid chromatography (HILIC) separation methods were developed and the resulting methods were used for the HPLC-UV-HRMS/MS analysis of the methanol extracts of the flowers, stems and leaves of the plant. The UV spectra obtained for 5 of the 8 major constituents provided corroborating evidence that the compounds of interest are flavonoids. The high resolution MS/MS spectra provided accurate masses for the precursor and product ions from which the molecular formulae could be deduced. The molecular formulae was subsequently compared to those reported in literature and a number of possible known molecular structures that produced the same precursor and product ions were found. It was then possible to identify an aglycone, apigenin [5,7-Dihydroxy-2-(4-hydroxyphenyl)-4H-1-benzopyran-4-one], a cell permeable polyphenol bioactive (anti-inflammatory, antioxidant) component and four different kinds of apigenin-O-glycosides, as well as three chlorogenic acid analogues.

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