Menthone and isomenthone biosynthesis in Pelargonium tomentosum Jacq

Pelargonium tomentosum was fed with aqueous solutions of different deuterium labelled monoterpenoid precursors. After headspace extraction with solid phase microextraction (SPME) the essential oil was analyzed with enantioselective multidimensional gas chromatography/mass spectrometry (enantio-MDGC/MS). Labelled piperitone with different enantiomeric distributions led to labelled (-)-isomenthone and labelled (+)-menthone in the same ratio as genuine (-)-isomenthone and (+)-menthone. Furthermore, labelled pulegone, piperitenone, piperitole and citronellyl glycopyranoside were investigated.