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Bioassay-guided isolation of apigenin with GABA-benzodiazepine activity from Tanacetum parthenium
Extracts of Tanacetum parthenium are used in prophylactic treatment of migraine. The plant has also been used in traditional Danish folk medicine for the treatment of epilepsy. In a screening of plants used to treat epilepsy and convulsions in Danish folk medicine an ethanolic extract of T. parthenium showed high affinity for the GABAA-benzodiazepine site .
Arial parts of Tanacetum parthenium Sch. Bip (100g) were defatted with petroleum ether, and then extracted with ethanol. The extract was partitioned between water and ethyl acetate. The ethyl acetate phase was subjected to VLC eluted with mixtures of toluene:ethyl acetate and ethyl acetate:ethanol. The active fraction from the VLC was further purified by semi-prep HPLC on a RP18 column with a gradient of methanol:5% formic acid at 5 mL/min. Structure elucidation was done by 1H-NMR. Activity was tested at each separation step in the 3H-Ro 15–1788 (Flumazenil) binding assay .
The bioassay-guided fractionation led to isolation of apigenin. The structure was confirmed by comparison with a commercial apigenin sample. The IC50 for apigenin was 24µM (diazepam IC50 0.1µM). Apigenin is known to bind to the GABA-A benzodiazepine site.
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