Electron ionization mass spectrometric fragmentation and multiple reaction monitoring quantification of trimethylsilyl derivatives of cucurbic acid and its 6,7-stereoisomers.

Rationale: Isomeric cucurbic acids derive from the reduction of the keto group of jasmonic acids. These growth regulators are natural constituents of various higher plants and fungi. Elucidation of electron ionization mass spectrometry (EIMS) fragmentation pathways of the trimethylsilyl (TMS) derivatives of the different stereoisomers is essential for their characterization and quantification in natural samples.