Structural analysis of platycosides in Platycodi Radix by liquid chromatography/electrospray ionization-tandem mass spectrometry

Abstract

Platycosides extracted from Platycodi Radix were analyzed by HPLC coupled with electrospray ionization multistage tandem mass spectrometry (HPLC/ESI-MS n ). Predominant [ M + Na] + ions in positive mode and [ M − H] − ions in negative mode in the direct ESI-MS spectra of extract provided information on molecular weights, but minor components and isomers could not be discriminated. However, combining HPLC and ESI-MS n , allowed eleven platycosides, including four acetylated platycodin isomers and two prosapogenines to be analyzed. During MS 2 analysis conducted to elucidate the structures of platycosides, fragment ions provided information on sugar moieties attached at C-28 of triterpene structure of the platycosides. Glycosidic bond cleavages at C-3 were revealed by fragment ions in MS 3 spectra. Some characteristic fragment ions not related to sugar bond cleavage revealed that an esterified triterpene is linked to sugars at C-28. The only sugar ring-cross cleavage corresponding to 90 Da in the negative MS 2 spectrum took place at an arabinosyl sugar moiety. By using HPLC/ESI-MS n , three acetylated platycosides in Platycodi Radix extract were newly identified.