Biosynthesis of menthofuran in Mentha x piperita: Stereoselective and mechanistic studies

Mentha x piperita shoot tips and first leaf pair were fed with aqueous solu tions of [H-2(2)]- and [H-2(2)]/[O-18]-labeled pulegone. The essential oil was analyzed by solid phase microextraction and enantioselective multidimen sional gas chromatography/mass spectrometry. After feeding experiments with labeled pulegone racemate, both labeled (S)-menthofuran and (R)-menthofura n were detectable simultaneously together with genuine (R)-menthofuran. It could be shown that both labeled pulegone enantiomers are converted by Ment ha x piperita to the corresponding labeled menthofuran enantiomers, favorin g the labeled analogue of the nongenuine (S)-pulegone. The oxygen in mentho furan is introduced by enzymatic oxidation of pulegone, as concluded from f eeding experiments with mixed labeled [H-2(2)]/[O-18]pulegone.