Different stereoselectivity in the reduction of pulegone by Mentha species

Aqueous solutions of [2H]-labeled pulegone enantiomers were fed to Mentha spicata ssp. spicata L. and Mentha spicata ssp. crispata L. shoot tip and first leaf pair. After solid phase microextraction the essential oil was analysed with enantioselective multidimensional gas chromatography/mass spectrometry. Both Mentha spicata species were able to convert labelled (1R)- and (1S)-pulegone at the same rate into the corresponding menthone and isomenthone, indicating an unspecific process. The reduction of both pulegone enantiomers preferably led to the cis-stereoisomers. The observed stereoselectivity is completely different from those of pulegone reduction by Mentha x piperita L.