Prallethrin

Chemical properties

solid

The Uses of Prallethrin

Prallethrin ia a synthetic pyrethroid; propynyl analog of allethrin. Prallethrin is used as an insecticide.

The Uses of Prallethrin

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.

Hazard

A poison by ingestion and inhalation. Low toxicity by skin contact.

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).

Safety Profile

A poison by ingestion and inhalation. Low toxicity by skin contact. When heated to decomposition it emits acrid smoke and irritating vapors.

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).