A new cyclopeptide alkaloid from Hymenocardia acida

Abstract

Hymenocardia acida Tul. (Euphorbiaceae) is a shrub or a small tree of about 6 m high, which grows in the savannah regions of Africa. The extracts are widely used in traditional African medicine, for example for their antiplasmodial and antidiabetic potential. Previous phytochemical studies on this plant have established the presence of alkaloids, anthocyanins, anthraquinones, cardiac glycosides, flavonoids, phenols, saponins, steroids, stilbenoids, tannins and triterpenoids [1, 2], but not much is known yet about the active compounds. In this study the isolation of alkaloids from H. acida is described. The dried root bark of H. acida (2.7 kg) was extracted by percolation with 80% methanol and fractionated by liquid-liquid separation and flash chromatography. To indicate the presence of alkaloids the Dragendorff and iodoplatinate reagent, two alkaloid specific TLC visualization reagents, were used and fractions which showed a positive reaction with both were selected for further analysis. The main compounds in these fractions were then isolated by semi-preparative HPLC-DAD-MS. In order to elucidate the structures of these compounds, 1H-, 13C- and a variety of 2D-NMR spectra were recorded. Compound 1, hymenocardine, has been isolated from this plant before [3] and the structure was confirmed by comparison with previously reported 1 H- and 13C-NMR spectra [3, 4]. Compound 2 was almost identical to compound 1, but the spectroscopic data showed that it contained a hydroxyl group instead of a carbonyl group and thus it was named hymenocardinol. To our knowledge it is the first time hymenocardinol was isolated from H. acida or any other natural source, although it has been prepared by reduction of hymenocardine. Thus, hymenocardinol is reported here as a new cyclopeptide alkaloid.