Structural Characterization of Polar Steroid Compounds of the Far Eastern Starfish Lethasterias fusca by Nanoflow Liquid Chromatography Coupled to Quadrupole Time-of-Flight Tandem Mass Spectrometry.

Nanoflow liquid chromatography coupled with a captive spray ionization time-of-flight tandem mass spectrometer (nLC/CSI-QTOF-MS/MS) was used in the structural determination of polar steroid compounds of starfish Lethasterias fusca. A total of 207 compounds including 106 asterosaponins, 81 glycosides of polyhydroxysteroids, and 14 polyhydroxylated steroids were detected and characterized by MS and MS/MS. Twenty compounds among them were unambiguously identified using authentic standard compounds, isolated earlier from this and other starfish species. The other compounds were tentatively characterized by accurate mass measurement and comparing retention times and characteristic MS/MS fragmentation patterns with reference standards. Moreover, fragmentation behaviors of a series of pure standards of starfish polar steroids and polyhydroxysteroid compounds detected in L. fusca have been extensively investigated and characteristic fragmentation pathways were described and used for the characterization of unknown compounds.