Metabolomic evaluation of three Digitalis species (fam. Plantaginaceae) using liquid chromatography with multistage mass spectrometry

Abstract

The aim of this research was to determine inter-species diversity in qualitative composition of methanol-soluble metabolites in leaves of three Digitalis species (D. lanata, D. ferruginea, and D. ambigua) from the central Balkans. Using the UHPLC-LTQ OrbiTrap MS technique, a total of 119 compounds were identified based on their monoisotopic masses, MSn fragmentation, and previously reported MS data. All indetified compounds were clustered into seven groups: steroidal glycosides (43 compounds), steroid aglycones (12 compounds), phenylethanoid glycosides (15 compounds), flavonoid glycosides (18 compounds), flavonoid aglycones (9 compounds), phenolic acid derivatives (14 compounds), and 8 compounds belonging to other classes. In addition to the expected cardiac glycosides, steroidal saponins and pregnane and furostanol glycosides were also abundant in the extracts of analysed Digitalis species. A detailed LC/MS qualitative analysis revealed very similar profiles of steroidal glycosides in extracts of D. lanata and D. ferruginea leaves, which were characterized by significant amounts of pharmaceutically important digoxin, deslanatoside, and lanatosides A, B, and C. On the other hand, these compounds were not detected in leaves of D. ambigua. The UHPLC-LTQ OrbiTrap MS method was proved to be simple, rapid, and accurate strategy for unambiguous taxonomic determination and chemical differentiation of Digitalis species. It also alowed the selection of high-resolution chemical markers for revealing inter- and intra-population variability of Digitalis species adopting targeted metabolomic approach, which is the course of our further work.