Food Chem. 2003 Nov 19;51(24):7055-61.
insecticide photochemistry, metabolism, and GABAergic action:
ethiprole compared with fipronil.
P, Sammelson RE, Casida JE.
Chemistry and Toxicology Laboratory, Department of Environmental
Science, Policy and Management, University of California,
Berkeley, California 94720-3112, USA.
differs from fipronil, the major phenylpyrazole insecticide,
only in an ethylsulfinyl substituent replacing the trifluoromethylsulfinyl
moiety. This study compares their photochemistry, metabolism,
action at the gamma-aminobutyric acid (GABA) receptor, and
insecticidal potency. On exposure to sunlight as a thin
film, ethiprole undergoes oxidation (major), reduction,
and desethylsulfinylation but not desulfinylation whereas
the major photoreaction for fipronil is desulfinylation.
Metabolic sulfone formation is more rapid with ethiprole
than fipronil in human expressed CYP3A4 in vitro and mouse
brain and liver in vivo. High biological activity is observed
for the sulfide, sulfoxide, sulfone, and desulfinyl derivatives
in both the ethiprole and the fipronil series in GABA receptor
assays (human recombinant beta3 homomer and house fly head
membranes) with [(3)H]EBOB and in topical toxicity to house
flies with and without the P450-inhibiting synergist piperonyl
butoxide. On an overall basis, the
ethiprole series is very similar in potency to the fipronil