Differentiation between 3,4- and 4,15-Epoxyeudesmanolides by Electrospray Ionization Tandem Mass Spectrometry.

We investigated the fragmentation of the eudesmanolide-type sesquiterpene lactones 1-(4-hydroxymethacryloyloxy)-3,4-epoxy-8-hydroxyeudesm-11(13)-6,12-olide () and 1-(2,3-epoxyangeloyloxy)-4,15-epoxy-8-hydroxyeudesm-11(13)-6,12-olide () by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The elimination of the different ester substituent at C(1) directly from protonated and () led to the formation of two regioisomer product ions ( - RCOH). Further fragmentation of resulted from consecutive eliminations of HO and CO molecules. However, we identified four product ions that allowed for the differentiation between 3,4- and 4,15-epoxyeudesmanolides. The formation of these diagnostic ions was associated with the C(3)-O bond of compound , which propitiates the participation of the lone pair of the oxygen epoxide in the formation of through a Grob-Wharton-type fragmentation, then resulting in an alternative fragmentation pathway. These data can be useful for the fast differentiation between epoxyeudesmanolide regioisomers directly from extracts by liquid chromatography-tandem mass spectrometry (LC-MS/MS), as an alternative to NMR, or even for quantitation studies of these compounds using multiple reaction monitoring (MRM) scan.