| Abstract: | The insecticidal activity of several new fluorinated pyrethroids was measured using houseflies untreated and treated with piperonyl butoxide (PB). 10, 10-Difluorophenothrin and 10, 10-difluoroallethrin, which include fluorine atoms at a position most easily attacked by mixed function oxidases (mfo) in the acid moiety, showed smaller topical LD50 values on the PB-untreated flies than the parent insecticides but rather large values on the PB-treated flies, suggesting that the introduction of fluorine prevents metabolic oxidation, although it has a negative effect on the interaction with a target site. Monofluorinated analogues of phenothrin, in which the structure of chrysanthemic acid was rearranged, still had moderate insecticidal activity, but flies were scarcely killed by 7 fluoroallethrin into which fluorine was introduced at a position most easily oxidized by mfo in the alcohol moiety. Competitive oxidation of the fluorinated derivatives and the parent compounds showed that fluorine at both the 10- and 7′-positions stabilizes the alkenyl side-chains of the pyrethroids against selenium dioxide and m-chloroperoxybenzoic acid. Photochemical studies with 10, 10-difluorophenothrin indicated that the photo-instability of the cyclopropanecarboxylic part could not be improved by this modification. |
