Separation and toxicity of enantiomers of organophosphorus insecticide leptophos

Enantiomers of leptophos were separated by high-performance liquid chromatography with a Whelk-O1 column using 3% dichloromethane in n-hexane as mobile phase. Toxicity tests of leptophos enantiomers and racemate were performed with daphnia. Enzyme inhibition of leptohpos was carried out by using butyryl cholinesterase from horse serum and acetylcholinesterase from housefly heads. From the inhibition test of butyrylcholinesterase, the half-inhibitory concentrations, IC50, of (+)-leptophos, (−)-leptophos, and (±)-leptophos were 0.241, 1.17, and 1.05 g mL−1, respectively. No significant difference in IC50 in (−)-leptophos and (±)-leptophos was found. However, the IC50 of (+)-leptophos was significantly different from those of the others. In the inhibition test of acetylcholinesterase, the IC50 values of (+)-leptophos, (−)-leptophos, and (±)-leptophos were 14.01, 24.32, and 13.22 g mL−1, respectively. There was no significant difference in IC50 in (+)-leptophos and (±)-leptophos, although the IC50 of (−)-leptophos was significantly different from those of the others. From these results, leptophos—both enantiomers and racemate—seems to have higher neurotoxicity for mammals than for the target insects. In the toxicity test of daphnia, the half-lethal concentrations, LC50, of (+)-leptophos, (−)-leptophos, and (±)-leptophos were 0.0387, 0.802, and 0.0409 g L−1, respectively. There is no significant difference in LC50 in (+)-leptophos and (±)-leptophos. The LC50 of (−)-leptophos is significantly higher than those of the others. From these results, (−)-leptophos has lower toxicity to daphnia.