Enantioselective behavior and bioactivity of chiral tebuconazole in apples

Tebuconazole, a chiral triazole fungicide widely used in apple disease control, is commonly applied as a racemic mixture without differentiating between enantiomers. This study investigated the dissipation kinetics of tebuconazole enantiomers in various apple fruit varieties under field conditions using UPLC-MS/MS. Evidence of stereoselective degradation was found in Fuji and Hanfu apples, where (−)-R-tebuconazole showed faster degradation compared to (+)-S-tebuconazole, with half-lives of 15.59 and 19.12 d, and 16.91 and 21.02 d, respectively. In contrast, no enantioselective degradation was observed in Huahong variety apples. Furthermore, (−)-R-tebuconazole was found to exhibit 16.8−68.4 times more fungicidal activity than (+)-S-tebuconazole against three of the most common pathogens in apple groves, including Botryosphaeria berengeriana, Colletotrichum gloeosporioides, and Alternaria alternate. Molecular docking analysis revealed that (−)-R-tebuconazole had a shorter binding distance and lower energy with CYP51 protein than (+)-S-tebuconazole, shedding light on the mechanism behind these experimental findings. Therefore, the development of a pure (−)-R-tebuconazole stereoisomer appears to be a promising option in the near future, given its higher bioactivity and faster degradation rate compared to the racemic mixture. This study provided valuable insights into the stereoselective behavior and bioactivity of tebuconazole in apples. Regular monitoring and effective management of chiral pesticides are increasingly essential due to their potential impact on food safety, pesticide risk assessment, and environmental pollution.