Biosynthesis of the pyrethrins: unsaturated fatty acids and the origins of the rethrolone segment

Abstract

The biosynthetic origins of the rethrolone segment of the natural pyrethrins may be associated with linoleic or linolenic acid, and three hypotheses are outlined. By administration of suitable [2-¹⁴C]- and [10-¹⁴C]-labelled fatty acids, coupled with studies of their subsequent degradation, these hypotheses should be distinguishable. Administration of [10-¹⁴C]oleic acid to an homogenate of Chrysanthemum cinerariaefolium achenes gave an incorporation ratio into the rethrolones relative to chrysanthemic acid of 1 to 0.5–0.25. This, and the results of ozonolysis, seem best interpreted as indicating that oleic acid is degraded to acetate before incorporation. [2-¹⁴C] Linoleic acid was synthesized and administered, producing a label distribution between the rethrolones and chrysanthemic acid of 1 :0.14–0.08. Kuhn-Roth analysis indicates again a strong background of degradation to acetate, though there is more labelling in the cyclopentenone methyl and its accompanying C-3 than would be expected from a pure acetate pathway.