Discrimination of Regioisomeric and Stereoisomeric Saponins from Aesculus hippocastanum Seeds by Ion Mobility Mass Spectrometry.

Abstract

Modern mass spectrometry methods provide a huge benefit to saponin structural characterization, especially when combined with collision-induced dissociation experiments to obtain a partial description of the saponin (ion) structure. However, the complete description of the structures of these ubiquitous secondary metabolites remain challenging, especially since isomeric saponins presenting small differences are often present in a single extract. As a typical example, the horse chestnut triterpene glycosides, the so-called escins, comprise isomeric saponins containing subtle differences such as cis-trans ethylenic configuration (stereoisomers) of a side chain or distinct positions of an acetyl group (regioisomers) on the aglycone. In the present paper, the coupling of liquid chromatography and ion mobility mass spectrometry has been used to distinguish regioisomeric and stereoisomeric saponins. Ion mobility arrival time distributions (ATDs) were recorded for the stereoisomeric and regioisomeric saponin ions demonstrating that isomeric saponins can be partially separated using ion mobility on a commercially available traveling wave ion mobility (TWIMS) mass spectrometer. Small differences in the ATD can only be monitored when the isomeric saponins are separated with liquid chromatography prior to the IM-MS analysis. However, gas phase separation between stereoisomeric and regioisomeric saponin ions can be successfully realized, without any LC separation, on a cyclic ion mobility-enabled quadrupole time-of-flight (Q-cIM-oaToF) mass spectrometer. The main outcome of the present paper is that the structural analysis of regioisomeric and stereoisomeric natural compounds that represents a real challenge can take huge advantages of ion mobility experiments but only if increased ion mobility resolution is attainable.

J Am Soc Mass Spectrom. 2019 Aug 26. doi: 10.1007/s13361-019-02310-7. [Epub ahead of print]
Colson E1,2, Decroo C1,2, Cooper-Shepherd D3, Caulier G2, Henoumont C4, Laurent S4, De Winter J1, Flammang P2, Palmer M3, Claereboudt J5, Gerbaux P6.

1. Organic Synthesis and Mass Spectrometry Laboratory (S2MOs), University of Mons, 23 Place du Parc, 7000, Mons, Belgium.
2. Biology of Marine Organisms and Biomimetics Unit (BOMB), University of Mons, 23 Place du Parc, 7000, Mons, Belgium.
3. Waters Corporation, Altrincham Road, Wilmslow, SK9 4AX, UK.
4. Department of General, Organic and Biomedical Chemistry, NMR and Molecular Imaging Laboratory, University of Mons, 23 Place du Parc, 7000, Mons, Belgium.
5. Waters Corporation, Brusselsesteenweg 500, 1731, Zellik, Belgium.
6. Organic Synthesis and Mass Spectrometry Laboratory (S2MOs), University of Mons, 23 Place du Parc, 7000, Mons, Belgium. pascal.gerbaux@umons.ac.be.