LC–ESI-MS/MS characterization of strophanthin-K

Abstract A liquid chromatography–mass spectrometry (LC–MS) method was developed for the characterization of strophanthin-K, a mixture of cardiac glycosides extracted from the seeds of Strophanthus kombe . The method is based on the separation of the cardenolides using high performance liquid chromatography (HPLC) followed by detection with electrospray ionization mass-spectrometry (ESI-MS). Chromatographic separation of the analytes was achieved on a RP C-18 column using water: 1% formic acid in water (v/v):acetonitrile gradient mobile phase. Strophanthin-K glycosides studied in ESI-MS in negative ion mode formed abundant adduct ions [ M  + HCOO] − while the pseudomolecular ions [ M  − H] − are obtained in ESI-MS/MS experiments. Six different cardiac glycosides were identified and characterized: k-strophanthoside, k-strophanthin-β, helveticoside (erysimin), erysimoside, cymarin and neoglucoerysimoside. Forced degradation investigations done with strophanthin-K showed that k-strophanthidin (the aglycone of strophanthin-K glycosides) was the main product of degradation in acidic conditions; however, in basic conditions, the hydrolysis of the unsaturated 17β-lactones to the corresponding γ-hydroxy acids was the predominant degradation pathway.