Monoterpene biosynthesis in Agathosma crenulata (Buchu)

Young plants of Agarthosma crenulata (L.) Pillans were stem fed with aqueou s solutions of H-2(2) and O-18/H-2(2)-labelled monoterpene ketone precursor s. The essential oil was extracted by solid phase microextraction and subse quently analysed with enantioselective multidimensional gas chromatography- mass spectrometry. Both labelled pulegone precursors were converted into co rresponding labelled menthone, isomenthone and menthofuran with different e nantioselectivity. Feeding experiments with O-18/H-2-labelled pulegone prov ed an enzymatic conversion of pulegone to menthofuran and the loss of the p ulegone oxygen. Stereoselective analysis of all four isopulegone stereomers using octakis(2,3-di-O -butyryl-6-O -tert-butyldimethylsilyl)-gamma -cyclo dextrin or heptakis(2,3-di-O -acetyl-6-O -tert-butyldimethylsilyl)-beta -cy clodextrin allowed the detection of enantiopure (1S)-cis- and (1S)-trans-is opulegone (> 99%) in A. crenulata and buchu samples. Labelled isopulegone i s discussed as a suitable pulegone precursor. Feeding experiments regarding the biosynthesis of 3-oxo-p-menthan-8-thiol and 3-oxo-p-menthan-8-thiol ac etate are also reported. Copyright (C) 2001 John Wiley & Sons, Ltd.