Stereo and enantioselective separation and identification of synthetic pyrethroids, and photolytical isomerization analysis.

Abstract

Permethrin, cypermethrin and cyfluthrin are three important pyrethroids with similar structures and contain four, eight and eight stereoisomers, respectively. All the stereoisomers were completely resolved by a combination of achiral and chiral high-performance liquid chromatography with hexane/isopropanol as the mobile phase. The absolute configurations for the stereoisomers were also assigned on the basis of enantioselective resolution of permethrinic acid. For cypermethrin and cyfluthrin, although there is the only difference being one F atom substitution in cyfluthrin, the cis-I diastereomer exhibited a reversal of enantiomer order. Three specific stereoisomers were further isolated to investigate the photolysis and chiral stability of synthetic pyrethroids at the enantiomeric level. The results clearly revealed that significant isomerization occurred along with the photolysis process. The isomerization occurred at chiral 1-C position, 3-C position or both in the cyclopropyl ring, and the chiral 3-C exhibited a higher inversion tendency.