Empenthrin is a low molecular weight ester of (1R)-chrysanthemic acid
(2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropanecarboxylic acid). It
has a relatively high vapour pressure and, unlike most pyrethroids, it is
effective against flying insects. The molecule has three chiral centres and
geometric isomerism in the alcohol group but, with the exception of the
1R acid, the full isomer mixture is used. As the insecticide has been
developed for domestic use, it is unlikely that there will be a requirement
for metabolism studies in plants or for extensive environmental fate studies.
Its metabolism in rats has been reported, with particular attention
paid to the fate of the novel alcohol moiety. As with other pyrethroids,
ester cleavage and oxidation and conjugation of the alcohol metabolite
predominated. The fate of the chrysanthemic acids can be assessed by
reference to phenothrin.
