Phytochemical and bioactivity investigations on Aptosimum elongatum Engl. Extracts
Molahloe, Tsebo Sentle
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In ancient times, the use of plants for traditional medicinal purposes has formed the foundation of what we call modern medicine today. Phytochemical investigations of plants used in traditional medicine have led to the discovery of many active compounds used in drugs today. Aptosimum elongatum (Scrophulariaceae) is an indigenous South African plant that has been used by the Khomani bushman for traditional remedies, both human and veterinary. However, to our knowledge a full phytochemical investigation has never been performed on this plant. In the search for new bioactive constituents, the dried and ground aerial parts of A. elongatum were extracted consecutively with dichloromethane (DCM) and then methanol (MeOH). Five compounds were isolated from the two crude extracts via various chromatography techniques and were identified as glucosylated iridoids, a class of monoterpenoids. Several spectroscopic and spectrometry techniques were used for structure elucidation, including 1H and 13C 1D NMR, 2D COSY, HSQC, HMBC, and NOESY NMR experiments, high resolution electrospray ionization mass spectrometry, and infrared spectra. The methanol crude extract yielded four compounds, three of which were identified as the known glucosylated iridoids angeloside (formerly isolated from Angelonia integerrima (Scrophulariaceae)), geniposidic acid, formerly isolated from Gardenia jasminoides Ellis (Rubiaceae)), and caryoptoside (formerly isolated from Lamium album (Lamiaceae)), and one novel glucosylated iridoid esterified at C-7 with a foliamenthoyl group, closely related to picconioside IV (formerly isolated from Picconia excelsa (Oleaceae), but with an extra hydroxy group. This compound was also isolated from the DCM crude extract, together with a second novel glucosylated iridoid, identical to the previous compound except for foliamenthoyl esterification at both C-7 and C-6′′ (glucose moiety). The crude MeOH and DCM extracts of A. elongatum showed moderate antioxidant activity, but only the DCM extract exhibited moderate inhibition of acetylcholinesterase, and GABAergic activity. Of the isolated compounds, caryoptoside and the mono foliamenthoate derivative showed antioxidant activity, and only the mono foliamenthoate derivative tested positive for AChE inhibition. Due to time constraints the isolated compounds have not been tested in the GABAergic assay. Glucosylated iridoids have been isolated from a number of plants belonging to the Scrophulariaceae, and even from the Aptosimum genus, but this is the first report on a phytochemical study of Aptosimum elongatum.