Biosynthesis of irregular monoterpenes in extracts from higher plants

Extracts from Artemisia annua and Santolina chamaecyparissus converted ¹⁴C-labelled IPP, DMAPP and DMVC into artemisia ketone, its corresponding alcohol, lavandulol and trans-chrysanthemyl alcohol with up to 12.0 % incorporation of tracer. DMVC was the most effective precursor under standard conditions and led to unequal distribution of tracer in the C-5 moieties. The same extracts interconverted cis and trans-chrysanthemyl alcohols and their pyrophosphates, artemisia ketone, and artemisyl alcohol in up to 10·4% yields, but geraniol, nerol and linalol or their pyrophosphates were not precursors of any of these compounds. Formation of artemisia ketone and its alcohol from C-5 intermediates was enhanced by NAD⁺ and NADP⁺ but was unaffected by absence of oxygen. These co-factors did not affect the yields of lavandulol or trans-chrysanthemyl alcohol. These observations suggest closely related biogenetic pathways to the three irregular skeltons that do not involve the usual C-10 intermediates of monoterpene biosynthesis: i.e. the biogenetic isoprene rule is not obeyed.