Antidiabetic compounds from Hypoxis colchicifolia and Terminalia sericea.
In this project two medicinal plant species, namely Hypoxis colchicifolia Bak (Hypoxidaceae) and Terminalia sericea Burch. (Combretaceae), have been investigated and different compounds isolated and characterised. The aim of this study was to investigate the phytochemistry and antidiabetic activity of H. colchicifolia and T. sericea. H. colchicifolia (H. latifolia) is after H. hemerocallidea (African Potato) the second most important Hypoxis medicinal species with commercial value in South Africa. From the methanol extract of the corms, four phenolic derivatives, hypoxoside, a mixture of dehydroxyhypoxoside A and B and bis-dehydroxyhypoxoside were isolated, as well as an environmental impurity bisphenol A diglycidyl ether. This is the first study on the isolation of the dehydroxyhypoxoside B. The methanol extract of H. colchicifolia showed glucose lowering effects and low toxicity in vitro against C2C12 muscle cells and Chang liver cells. Of the pure compounds, only the mixture of dehydroxyhypoxoside A and B showed an increase in glucose utilization by the muscle cell line C2C12. T. sericea is an important plant in traditional medicine and is in the top 50 most important African medicinal plants. From the methanol extract of the roots, one known compound, sericic acid, was isolated. The methanol extract of T. sericea roots showed an increase in glucose utilization by C2C12 muscle cells and Chang liver cells but the extract also showed some cytotoxicity towards these cells. Structural elucidation of the different compounds was achieved by using NMR spectroscopy in one and two dimensions, high-resolution mass spectrometry, infrared spectroscopy and ultraviolet spectroscopy.