Characterization of triterpenoidic saponin mixture in crude extracts from leaves of Acanthopanax senticosus Harms by saponin structural correlation and mass spectrometry

Abstract

Eighteen triterpenoidic saponins in crude extracts from leaves of Acanthopanax senticous Harms have been investigated by electrospray ionization multi-stage tandem mass spectrometry and high-resolution mass spectrometry. In ESI-MS spectra, predominant [M + Na] + ions in the positive ion mode have been observed for molecular mass information. Meanwhile, specific structural correlations between these ions are firstly found. The 18 peaks (ions) can be classified into three groups (group D, E, and F with mass increase) with each group including six peaks. There is a mass difference of 132 Da between group D and E for each corresponding peak in turn (for example peak 1 to peak 7), indicating one more pentose residue was attached to saponins in group E than those corresponding in group D. The mass difference of 146 Da between group E and F implies one more deoxy-hexose attached to saponins in group F than those corresponding in group E. The structural correlations of the corresponding ions are confirmed by tandem mass spectrometry and high-resolution mass spectrometry. These structural features can not only facilitate the rapid characterization of the native known saponins in crude plant extracts, thus avoiding tedious derivation and separation of saponins, but also help find novel compounds of the same type in a specific medicinal plant. The structures of 14 known triterpenoidic saponins and four unknown saponins are thus determined or predicted. This methodology, with a combination of structural correlation of a complex mixture of homologs (which are difficult to separate) and mass spectrometry, has been established as a powerful and practical tool for the profiling of mixtures, especially of crude plant extracts and structural characterization of unknown compounds.