Rapid characterization of triterpene saponins from Conyza blinii by liquid chromatography coupled with mass spectrometry

Abstract

Conyza blinii Le'vl is a medicinal herb used for the treatment of inflammation in Chinese folk medicine. Its major bioactive constituents are triterpene saponins, most of which contain 6-8 sugar residues. In this report, electrospray ionization tandem mass spectrometry fragmentation behaviors of bisdesmosidic triterpene saponins (conyzasaponin A, B, and C) were studied in both positive and negative ion modes with an ion-trap mass spectrometer. In full scan mass spectrometry, these saponins gave predominant [M-H](-) and [M+Na](+) ions, which determined the molecular weights. In tandem mass spectrometry (MS(n), n = 2-4), the [M-H](-) and [M+Na](+) ions yielded fragments [Y(0α)-H](-) and [B(α)+Na](+), which were diagnostic for the structures of the triterpene skeleton and sugar chains. The structural elucidation was approved by accurate mass data using IT-TOF-MS. An interpretation guideline based on MS(n) (n = 2-4) diagnostic ions was proposed in order to elucidate the chemical structures of unknown triterpene saponins in C. blinii extract. The saponins in C. blinii were separated by liquid chromatography with a methanol/acetonitrile/water solvent system, and then analyzed by ion-trap and IT-TOF mass spectrometers. Based on the interpretation guideline, a total of 35 triterpenoid saponins were tentatively identified. Among them, 15 saponins had been previously reported, and the other 20 saponins were reported from Conyza species for the first time. This study indicates that LC/MS is a powerful technology for the rapid characterization of complicated saponins in herbal extracts.