Chiral Pesticide Penconazole: Bioactivity,Toxicity,and Stereoselective Degradation In Apples

Penconazole is a systemic chiral fungicide,belonging to the triazole family.It is widely applied in agricultural production.At present,it is produced,marketed,and used in racemic form,but it has not been systematically studied at enantiomer level.In this study,absolute configuration,stereoselective bioactivity,toxicity,and degradation in apples of penconazole were conducted.Firstly,the absolute configurations of penconazole stereoisomers were confirmed the theoretical electronic circular dichroism（ECD）spectra.The penconazole stereoisomers were identified as S-（–）-penconazole and R-（+）-penconazole.The two stereoisomers of penconazole were detected on a UPLC-MS/MS system with a Lux Cellulose-2 chiral column by systemically optimizing proportion of organic modifier,flow rate,and column temperature.Finally,the efficient and rapid method for the separation and analysis of two enantiomers of penconazole were established.Secondly,the fungicidal activity of penconazole and its stereoisomers were evaluated considering five target pathogens:Botriytis cinerea,Alternaria alternate f.sp.mali,Botryosphaeria berengeriana f.sp.piricola,Colletotrichum gloeosporioides,and Fusarium oxysporum.The results showed that the bioactivity of S-（–）-penconazole is significantly higher than R-（+）-penconazole.The bioactivity of penconazole in sequence is S-（–）-penconazole>rac-penconazole>R-（+）-penconazole.The bioactivity of S-（–）-penconazole was 1.8–4.4 times higher than that of R-（+）-penconazole considering the five fungi.Thirdly,penconazole inhibits methyl hydroxylation at the C-14α（CYP51）position of lanosterol,hindering the biosynthesis of sterol in fungi.Here,molecular docking was used to identify potential mechanisms for the stereoselective bioactivity of penconazole.It was proved that in comparison to R-（+）-penconazole,S-（–）-penconazole bound better with protein CYP51,the binding free energy for R-（+）-penconazole was higher than S-（–）-penconazole.The molecular docking analysis demonstrated that the bioactivity of S-（–）-penconazole was higher than that of R-（+）-penconazole,which was consistent with the results of the fungal phytopathogen fungicides inhibition experiment.Fourthly,an acute toxicity test of rac-penconazole and its two stereoisomers was undertaken considering Daphnia magna Straus.The acute toxicity,sequentially,was S-（–）-penconazole>rac-penconazole>R-（+）-penconazole;the eco-toxicity of S-（–）-penconazole was 32.5 and 6.5 times higher than that of R-（+）-penconazole at 24 h and 48 h,respectively.Based on the classification standard of pesticides to considering Daphnia magna Straus,S-（–）-penconazole was rated as highly toxic after 48 h(0.1<EC₅₀≤1.0 mg/L).Fifthly,the enantioselective dissipation of penconazole in apple was studied.The three apple-producing areas in China（Yantai of Shandong,Yuncheng of Shanxi,and Xingcheng of Liaoning）were selected.Furthermore,the degradation of penconazole enantiomers were also studied under fruit bagging conditions.It could be concluded that R-（+）-penconazole had a higher rate of degradation than S-（–）-penconazole in apples.The T_1/2of R-（+）-penconazole is 23.5–60.9 days and 23.0–57.5 in non-bagged apple and bagged apple,respectively;The two stereoisomers of penconazole were found to degrade at the fastest rates in Shanxi province in both non-bagged and bagged apples.No noticeable differences were observed in the half-life of R-（+）-penconazole in the non-bagged apples in all test regions,while it was distinctly different for S-（–）-penconazole half-life.Moreover,the half-life values of penconazole under bagging condition were extended significantly than those on non-bagging conditions,which indicated that degradation rate of penconazole was slower under bagging condition.Thus,the environmental risk of penconazole could possibly be underestimated through traditional risk assessment.Considering the high costs in preparing pesticide enantiomers,we suggest using penconazole raceme in agriculture.While considering the risk assessment at stereoisomeric levels,and tightening regulations for food and environmental safety.Furthermore,the molecular mechanisms of toxicity in penconazole need further exploration.This study provides a suitable basis to further investigation of penconazole.