Comprehensive evaluation of chiral penflufen metabolite (penflufen-3-hydroxy-butyl): Identification, synthesis, enantioseparation, toxicity and enantioselective metabolism

Identification and evaluations of pesticide metabolites are necessary for risk assessment and toxicological research. In this study, the metabolites of penflufen (a widely used chiral pesticide) in rat liver microsomes were identified using liquid chromatography Q-Exactive Plus mass spectrometry. In total, 17 penflufen metabolites were identified, and most of them were hydroxylation products, which were generated by oxygenation at different candidate sites of penflufen. The relative abundance of metabolite M12 (penflufen-3-hydroxy-butyl, 32 %) was the largest, followed by M8 (15.6 %) and M2 (12.8 %). The major metabolite penflufen-3-hydroxy-butyl was first synthesized by 11 reactions with a 99.73 % purity. The absolute configuration of M12 enantiomers were confirmed after preparing enantiomers, and establishing the enantioseparation method. The M12 enantiomers toxicity to Danio rerio (LC₅₀, >10 mg/L) and four kinds of phytopathogens (EC₅₀, 148–34969 mg/L) were significantly lower than parents (LC₅₀, 0.449–24.3 mg/L; EC₅₀, 0.027–92.0 mg/L). In rat liver microsomes, approximately 40–47 % of the penflufen enantiomers were metabolized to M12 enantiomers, and R-penflufen was preferentially metabolized. The generation concentrations of S-M12 were higher than R-M12 after 10 min, and the metabolic half-lives of R-M12 (29.0–32.5 min) were shorter than S-M12 (35.2–38.1 min), and were approximately 4 times longer than parent penflufen enantiomers (4.5–9.5 min). Simultaneously, the generated contents (relative contents) of M8 (27.1–57 %) and M10 (2.22–8.36 %) from S-penflufen were lower than those from R-penflufen (M8, 24.7–92.4 %; M10, 27.4–69.5 %). The enantioselective evaluations of M12, M10 and M8 deserve further study. These findings were helpful in understanding the fate and risks of chiral penflufen.