Differentiation between 34- and 415-Epoxyeudesmanolides by Electrospray Ionization Tandem Mass Spectrometry

摘要

We investigated the fragmentation of the eudesmanolide-type sesquiterpene lactones 1α-(4-hydroxymethacryloyloxy)-3α,4α-epoxy-8α-hydroxyeudesm-11(13)-6α,12-olide (>1) and 1α-(2,3-epoxyangeloyloxy)-4α,15-epoxy-8α-hydroxyeudesm-11(13)-6α,12-olide (>2) by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The elimination of the different ester substituent at C(1) directly from protonated> 1 and> 2 (>A) led to the formation of two regioisomer product ions> B (>A − RCO2H). Further fragmentation of> B resulted from consecutive eliminations of H2O 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> 1, which propitiates the participation of the lone pair of the oxygen epoxide in the formation of> B 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 Dimerostemma 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.