Synthesis and bioactivity of tetrahydrothiopyran derivatives as potential acaricides against Psoroptes cuniculi.

Thirty-two tetrahydrothiopyran derivatives were synthesized, and their acaricidal activities against Psoroptes cuniculi were evaluated in vitro. The results showed that eight compounds exhibited higher acaricidal activity than ivermectin when evaluated by mass concentration, while six compounds showed superior activity when assessed by molar concentration. Compound b10 showed the lowest LC₅₀ value [62.3 µg/mL (0.12 mM)] and LT₅₀ value (2.2 h at 4.5 mM), far lower than ivermectin [LC₅₀ = 223.3 µg/mL (0.26 mM), LT₅₀ = 8.7 h]. Structure-activity relationship (SAR) analysis showed that the presence of the sulfone structure is crucial for activity, while the types and positions of substituents on the benzene rings are two main factors affecting the activity. Molecular docking results demonstrated that compounds a10, b9, b10 and b11 exhibited good affinity with the AChE protein, along with potential binding modes, suggesting AChE as a promising acaricidal drug target. Overall, these results suggest that tetrahydrothiopyran derivatives, particularly their sulfone derivatives have great potential for the development of novel acaricides.