The major phenolic compound of the roots and leaves of Rafnia amplexicaulis (Fabaceae), a liquorice substitute and traditional tea used in Cape Herbal Medicine

Abstract

The roots of Rafnia amplexicaulis have been used as a substitute for liquorice root and the leaves as a traditional medicinal tea in Cape (Khoi-San and Cape Dutch) Herbal Medicine. All published ethnobotanical data are presented, showing that two other species, Rafnia acuminata and Rafnia angustifolia, have also been used as a source of tea. The major compound of the roots and leaves of Rafnia amplexicaulis, responsible for the intense bittersweet taste, was isolated and identified as 8-glucopyranosyl-4,5,7-trihydroxyisoflavone (genistein 8-C-β-d-glucoside). The structure was determined on the basis of NMR and MS data, as well as X-ray crystallographic analysis. R. amplexicaulis and related species are a newly discovered source of this isoflavone (a compound with demonstrated antioxidant and radioprotective effects) that may be at least partly responsible for the traditional uses in treating asthma, influenza, back problems, infertility, catarrh and wasting. Rafnia species may therefore have potential value as new ingredients of herbal teas and functional foods.