Stereospecific fragmentation of starfish polyhydroxysteroids in electrospray ionization mass spectrometry

Electrospray ionization mass spectra and collision-induced dissociation mass spectra in positive and negative ion modes of five polyhydroxysteroid compounds from starfish were studied. Tandem mass spectra exhibit extensive fragmentation, including sequential neutral losses of H2O molecules and cleavages in the tetracyclic nucleus and side chains. The relative intensity of some peaks in tandem mass spectra enables stereoisomers with the different orientations of the hydroxyl group at C15 in the tetracyclic nucleus to be distinguished. Some data on the fragmentation mechanisms were obtained by H-D exchange and mass spectrometry analysis.