Phytochemistry of Dais cotinifolia L.
Danca, Busisiwe Buyisile.
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Many plant-derived secondary metabolites have interesting biological activities and some plant compounds such as artemisinin (antimalarial) and vincristine (anticancer agent) are the active principles of main-stream pharmaceuticals. South Africa has an immense biodiversity and there are in the order of 25 000 indigenous plant species in the country. The phytochemistry of many of these plants has never been investigated. Many bioactive compounds have been isolated from the Thymelaeaceae, such as prostatin (potent anti-HIV agent) and antitumour diterpenoids. Although a large number of Thymelaeaceae species are indigenous to South Africa, only a limited number of species have been subjected to phytochemical investigations. Dais cotinifolia L. is one species on which phytochemical results have not been published and this tree was the subject of this investigation. Four compounds were isolated from D. cotinifolia. Three of these compounds are known metabolites, two furofuran lignans, kobusin and eudesmin, and the flavonoid catechin. A fourth compound is novel norlignan, 2-hydroxy-5-(3-methoxyphenyl)-1-(4-methoxyphenyl)pentan-1-one. The compounds were isolated by applying different chromatographic procedures, such as column chromatography, preparative centrifugal thin-layer chromatography and semi-preparative high-performance liquid chromatography. The structural elucidation of the compounds was based on mass spectrometry and nuclear magnetic spectroscopy. The antioxidant activities of the crude extracts of the different plant parts were determined by the DPPH assay. In comparison with ascorbic acid, the crude extracts only had mild antioxidant activities. The mild activities of the extracts can be explained by the fact that three of the compounds isolated are aromatic compounds, but have methoxy substituents and not free phenolic groups, which are often associated with high-antioxidant activity.