Terpene biosynthesis. Part III. Biosynthesis of (+)- and (–)-camphor in Artemisia, Salvia, and Chrysanthemum species

Abstract

(+)-Camphor biosynthesised from [2-¹⁴C]mevalonic acid by Artemisia californica or Salvia leucophylla L., and (–)-camphor similarly formed by Chrysanthemum balsamita L., contained 73–83% of the incorporated tracer at C-6 atom. The balance was fairly evenly distributed amongst the other carbon atoms. Isopentenyl pyrophosphate was thus the predominant radioactive precursor and, as was found for thujane derivatives produced by related species, that part of the skeleton derived from 3,3-dimethylallyl pyrophosphate was not equivalently labelled. The similarity of the labelling pattern for both optical isomers is consistent with each being formally derived from the cation formed from the corresponding enantiomer of α-terpineol by addition of the positive centre to the double bond. The formation of both optical isomers of camphor from a particular enantiomer of α-terpineol by cyclisation to C-2 and C-6, respectively, was ruled out.