Database of African Theses and Dissertations including Research (DATAD-R)

Isolation of bioactive constituents from seeds of Schotia brachypetala (Fabaceae) and Colophospermum mopane (Fabaceae)

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dc.contributor Marston, Andrew
dc.contributor Van der Westhuizen, Jan
dc.creator Du, Kun 2017-03-15T07:35:47Z 2017-03-15T07:35:47Z 2011-11 2018-06-24T05:28:09Z 2018-06-24T05:28:09Z
dc.description Natural products play an important role in drug discovery, as scaffolds and new skeletons. It is remarkable to note that in 2007, natural products were implicated in the development of 52% of all new drugs. These compounds give “smart structures” rather than a much larger random collection of assemblies, which results, for example, from combinatorial chemistry or computer modeling. As part of our natural heritage, higher plants are a potential source of millions of bioactive products with an almost infinite variety of different structural variations, and they represent an enormous store of valuable pharmacological molecules waiting to be discovered. South Africa is one of the richest centers of plant diversity in the world, thus providing a fantastic collection of natural products. Of the different South African plant parts, seeds have been little studied from a chemical viewpoint but, in light of their function, may have interesting metabolites. Twenty-five species were collected based on a variety of information from traditional medicine, seed size and availability, and random collection. Seeds of trees were principally selected because these are often large and easier to handle. Extraction was with methanol, to minimize the quantity of oil in the sample. A total of 29 extracts were screened for biological activities. The methanol extracts of the aril of Schotia brachypetala Sond. (Fabaceae) seeds, and the premature seeds of Colophospermum mopane (Kirk ex Benth.) J. Leonard (Fabaceae) were selected for further investigation since they had significant biological activities. Fractionation and isolation were achieved mainly by using high-speed countercurrent chromatography. Biological assays, including free-radical scavenging activity, inhibition of acetylcholinesterase, antimicrobial and antimalarial testing, were used for activity-guided fractionation and for the activity assessment of extracts, fractions, and isolates. The structures of pure compounds were determined mainly by spectroscopic methods (UV, MS, NMR, CD) and some chemical methods. A total of 9 compounds were isolated from these two species, of which 2 were new compounds. The principles responsible for the biological activities of the extracts were also identified. From the methanol extract of the aril of Schotia brachypetala, 7 quercetin glucoside derivatives were isolated: 3-O-methylquercetin 7-O-β-glucopyranoside (A), 3,4ʹ-di-O-methylquercetin 7-O-β-glucopyranoside (B), 3-O-methylquercetin 7-O-[β-D-6ʹʹ(E-p-coumaroyl)glucopyranoside] (C), 3,4ʹ-di-O-methylquercetin 7-O-[β-D-6ʹʹ(E-p-coumaroyl)glucopyranoside] (D), quercetin 7-O-β-glucopyranoside (E), (2R, 3R)-dihydroquercetin 7-O-β-glucopyranoside (F) and quercetin 3-O-[2-O-β-xylopyranosyl-6-O-α-rhamnopyranosyl]-β-glucopyranoside (G). Five of them showed DPPH radical scavenging activity. One of the new compounds gave the strongest radical scavenging activity. The pure compounds A and C were also weakly active as antimalarials. From the methanol extract of Colophospermum mopane premature seeds, two compounds were characterized. One was the sesquiterpene β-caryophyllene oxide (I) and one was a diterpenoid (H). The stereochemistry of the latter was analyzed with the help of NMR spectroscopy and, in particular, NOE experiments. The diterpenoid showed antimicrobial activity and potent acetylcholinesterase inhibition.
dc.description National Research Foundation (NRF)
dc.language en
dc.publisher University of the Free State
dc.rights University of the Free State
dc.subject Dissertation (M.Sc. (Chemistry))--University of the Free State, 2011
dc.subject Seeds
dc.subject Schotia brachypetala
dc.subject Colophospermum mopane
dc.subject Leguminosae
dc.subject Fabaceae
dc.subject Flavonol glycosides
dc.subject Diterpene
dc.subject Caryophyllene oxide
dc.subject Antimalarials
dc.subject Antimicrobials
dc.subject Radical scavengers
dc.subject Acetylcholinesterase inhibitors
dc.subject Plant bioactive compounds
dc.subject Legumes-- Molecular aspects
dc.subject Materia medica, Vegetable
dc.subject Medicinal plants
dc.subject Molecular botany
dc.title Isolation of bioactive constituents from seeds of Schotia brachypetala (Fabaceae) and Colophospermum mopane (Fabaceae)
dc.type Dissertation

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