Structural characterization of steroidal saponins by electrospray ionization and fast-atom bombardment tandem mass spectrometry.

The structural characterization of four steroidal saponin compounds involving two and three sugar groups, namely spirostanol saponins and furostanol saponins, were investigated by positive ion fast-atom bombardment (FAB), electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS) techniques. Important structural information was obtained from collision-induced dissociation (CID) and FAB-MS spectra with different liquid matrices. It was found that a characteristic fragmentation involving the loss of 144 Da arising from the cleavage of the E-ring was observed when there was no sugar chain at the C-26 position. When a glucoside group was substituted at the C-26 position, this C-26 sugar moiety was preferentially eliminated. All of these compounds produced a major product ion with a stable skeleton structure at m/z 255. The results of this paper can assist structural analysis of mixtures of steroidal saponins.