Hazard
A poison by ingestion and inhalation. Low
toxicity by skin contact.
Uses
Prallethrin ia a synthetic pyrethroid; propynyl analog of allethrin. Prallethrin is used as an insecticide.
Uses
Prallethrin is used for the control of insects in domestic and public
health situations.
Definition
ChEBI: Prallethrin is a member of cyclopropanes and a terminal acetylenic compound. It has a role as a pyrethroid ester insecticide and an agrochemical. It is functionally related to a chrysanthemic acid.
Pharmacology
Prallethrin is a propynyl analog of allethrin, with
2-methyl-4-oxo-3-(prop-2-ynyl)-cyclopent-2-enyl as the
secondary alcohol moiety that has been introduced against
public health pests (113–115). The ester of the (S)-alcohol
with (1R)-trans,cis-chrysanthemic acid resolved partially
is commercialized on the strength of the assessment of
insecticidal action of individual stereoisomers (116). Compared
with d-allethrin, it is approximately four, six, and
five times more effective on Musca domestica (for killing),
Blattella germanica (for killing), and Culex pipiens pallens
(for knockdown), respectively (43). A lower level of resistance
to prallethrin than to phenoxybenzyl pyrethroids
was demonstrated in a kdr-resistant housefly strain (116).
Metabolic pathway
Prallethrin is stable under normal room temperature storage conditions
for up to 36 months. It is labile to alkali at the ester linkage, forming 2
and 3 (Scheme 1). Analogy with the allethrins (from which it differs
only in the degree of unsaturation in the side chain - propyne rather
than propene) would suggest that the compound is very photolabile.
Degradation
The metabolism of prallethrin was studied following single oral administration
and subcutaneous injection of the cis- and trans-isomers to rats at
two dose levels and after repeated dosing. The compound was labelled in
the alcohol moiety (inferred from the results) (PSD, 1995).
Absorption was rapid with maximum tissue residues being attained
3 hours after the dosing of each isomer. Biphasic clearance of radioactivity
then occurred with half-lives of 3 and 14-23 hours (cis-isomer) and 3-5
and 7-35 hours (trans-isomer). Urinary excretion accounted for 13-32%
(cis-isomer) and 45-62% (trans-isomer) of the dose with most of the balance in the faeces. Less than 0.1% was exhaled as 14CO2 . Residues
in tissues were very low (0.3% of the dose at 7 days). Metabolism and
disposition were independent of dose and dose route but residues in
tissues were somewhat higher for the cis-isomer.
Twenty-one metabolites were identified (taking account of stereochemistry
and conjugates). The major pathways of metabolism involved
oxidation at a methyl group of the isobutenyl group in the acid moiety
(giving 4 and 5), at the C1 and C2 positions of the propynyl group in the
alcohol moiety (giving 6 and 9) and dihydroxylation (to 7 and 8). The
resulting hydroxy derivatives were conjugated with glucuronic acid and
sulfate.
Hydrolysis of prallethrin also occurred to afford the acid 2 (presumed)
and the alcohol 3. Hydrolysis of the hydroxylated prallethrins and further
oxidation of 3 afforded 10 and 11. Further oxidation of 10 to the cyclic
tertiary alcohol (12) was observed.
When bluegill sunfish were exposed to a l4C-labelled (acid and alcohol
groups) prallethrin isomer (1Rtrans), more than 50% of the biliary
radioactivity recovered from the gall bladder was observed as one ester metabolite. This was identified as the taurine conjugate of carboxylic acid
metabolite 5 (Oshima et al., 1992).
