Chiral Organophosphorous Pesticide Fosthiazate: Absolute Configuration, Stereoselective Bioactivity, Toxicity, and Degradation in Vegetables

Abstract

Fosthiazate is a widely used chiral organophosphorous nematicide with four stereoisomers. The present study systemically assessed the stereoselectivity of fosthiazate for the first time, including absolute configuration confirmation, stereoselective bioactivity toward nematode and aphid, toxicity to honeybees, and stereoselective degradation in cucumber and pepper under field conditions. The absolute configurations of the four stereoisomers that eluted on the Superchiral IG-3 column were confirmed as (1S,3R)-(-)-fosthiazate, (1S,3S)-(-)-fosthiazate, (1R,3S)-(+)-fosthiazate, and (1R,3R)-(+)-fosthiazate. In comparison to the other two stereoisomers, (1S,3R)-fosthiazate and (1S,3S)-fosthiazate possess more than 100 times bioactivity and 10 times toxicity toward the target and non-target organisms, respectively. The molecular docking found that (1S,3R)-fosthiazate and (1S,3S)-fosthiazate had shorter binding distances and lower energies with acetylcholinesterase (AChE), which illuminated the mechanism of the experimental results. In addition, both of the high-bioactive stereoisomers had faster degradation rates in cucumber and pepper. On the basis of the results of bioactivity, toxicity, and degradation behavior, the stereoisomer mixture with (1S,3R)-fosthiazate and (1S,3S)-fosthiazate will be a better option than racemic fosthiazate to increase the bioactivity and reduce application rates.