Pydiflumetofen, as a new succinate dehydrogenase inhibitor (SDHI) chiral fungicide, has been used in crop production because of its broad-spectrum and high-efficiency antifungal activity. However, little literature is known about pydiflumetofen at the chiral level. In the present study, a sensitive enantioselective determination method based on UHPLC-MS/MS coupled with Lux Cellulose-2 chiral column for pydiflumetofen enantiomers, and quantitative determination in food and environmental samples, was successfully developed and validated. And the absolute configuration of the first eluted peak was confirmed as S-(-)-pydiflumetofen and the second peak was R-(+)-pydiflumetofen by comparing the calculated ECD spectra and experimental as well as measuring the optical rotation. Then, the stereoselective bioactivity against the seven targeted phytopathogens, the acute toxicity to different life stages of zebrafish (embryo, larva, and adult), and degradation of pydiflumetofen in different vegetables (cucumber, eggplant, and cowpea) and soil were investigated. Pydiflumetofen presented effective bioactivity against the tested phytopathogens. Moreover, the bioactivities of R-pydiflumetofen were 49.4~958.8 times higher than that of S-pydiflumetofen and nearly twice than that of Rac-pydiflumetofen. According to the molecular docking study, R-enantiomer could bind more tightly to the target protein (SDH) with the shorter binding distance (TRP B-230 and TRY D-144, with the distance of 2.2 Å and 1.8 Å, respectively) and lower energy affinity (-7.0 kcal mol^-1) than S-enantiomer, which could illuminate the reason for the stereoselective activity. Otherwise, the toxicity results showed that pydiflumetofen has high toxicity to different life stages of zebrafish, while the embryo constitutes the most sensitive period of zebrafish to pydiflumetofen. And the toxicity of R-enantiomers was nearly 10 times higher than S-enantiomers in the 96-h acute toxicity test. Nevertheless, there was no significant difference between R-pydiflumetofen and Rac-pydiflumetofen. Besides, the results of field degradation experiments revealed that R-(+)-pydiflumetofen was preferential degradation in vegetables and soil. Consequently, R-pydiflumetofen not only exhibited a higher bactericidal activity with less dose but also had fewer environmental risks in the environment, which can provide scientific guidance and assertive evidence for developing the high-efficiency and low-risks fungicide.

Zhen Wang

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