Separation and toxicity of enantiomers of organophosphorus insecticide leptophos

Yen, Jui-Hung, Chia-Chun Tsai and Yei-Shung Wang

Department of Agricultural Chemistry, National Taiwan University, Taipei 10617, Taiwan

Abstract

Enantiomers of leptophos were separated by high performance liquid chromatography with a Whelk-O 1 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 concentration, IC₅₀ , of (+)-Leptophos, (-)-Leptophos, and (±)-Leptophos was 0.241, 1.17, and 1.05 g mL^-1, respectively. No significant difference of IC₅₀ between (-)-Leptophos and (+)-Leptophos was found. However, the IC₅₀ of (+)-Leptophos was significantly different from the others. In the inhibition test of acetylcholinesterase, the IC₅₀ values of (+)-Leptophos, (-)-Leptophos, and (±)-Leptophos is 14.01, 24.32, and 13.22 g mL^-1, respectively. There was no significant difference of IC₅₀ between (+)-Leptophos and (±)-Leptophos, although the IC₅₀ of (-)-Leptophos was significantly different from 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 of LC₅₀ between (+)-Leptophos and (±)-Leptophos. The LC₅₀ of (-)-Leptophos is significantly higher than the others. From these results, (-)-Leptophos has lower toxicity to daphnia.

Key words: HPLC, Enantioseparation, Leptophos, Whelk-O 1 column.