Glycosylation of Cardenolide Aglycones in the Leaves of Nerium oleander

Abstract

Application of [¹⁴ C]-progesterone to the leaves of Nerium oleander L. (Apocynaceae) resulted in the formation of [¹⁴ C]-digitoxigenin and [¹⁴ C]-oleandrigenin glycosides; the labelled aglycones were obtained after hydrolysis from the cardenolide extract. Both radioactive cardenolide aglycones were further transformed by the leaves of Nerium oleander L. to the corresponding 3-O-β-glucosides digitoxigenin glucoside and oleandrigenin glucoside. It could be shown that both cardenolide glucosides are genuine constituents of the cardenolide fraction of Nerium oleander L. leaves. The structures of these newly identified compounds were verified by ¹H-NMR and FAB⁺ mass spectroscopy and by enzymatic cleavage of the glycosidic bond with a β-glucosidase from Helix pomatia.