Redox interconversions of geraniol and nerol in higher plants

Use of ¹⁴C, ³H-labelled precursors showed that for feedings carried out in winter, isothujone (trans-thujan-3-one) was formed in Tanacetum vulgare from nerol (3,7-dimethyl-octa-cis-2,6-dien-1-ol) without loss of hydrogen from C-1 of the precursor. In contrast, formation from geraniol (the corresponding trans-isomer) involved stereospecific loss ofthe pro-(1S) hydrogen. This suggests that geraniol and nerol were interconverted by a redox system. Similar studies at other seasons with T. vulgare and on the biosynthesis of α- and β-pinenes (pin-3-ene; pin-2-(10)-ene) in Pinus pinaster; 1,8-cineole (1,8-oxidomethane) in Mentha piperita and Eucalyptus globulus; and carvone (menth-6,8(9)-dien-2-one) in M. spicata did not lead to such unambiguous conclusions. The results may be rationalized if (i) the redox system was reversible and/or (ii) tracer at C-1 of the phosphate esters of the precursors was scrambled by action of a phosphatase that induced CO bond fission.