Discovery of HNPC-A188: a novel acaricide containing trifluoroethyl thioether and pyrimidin-4-amine

Pyrimidifen is an excellent commercial acaricide, but it is not low toxic to mammals. Trifluoroethyl thioether derivatives exhibit excellent bioactivity, and flupentiofenox is the first commercially available trifluoroethyl thioether acaricide. To search for novel pesticides, we conducted research around pyrimidifen and flupentiofenox. By introducing trifluoroethyl thioether and F, Cl, CH₃ substituents at different positions on the benzene ring, we successfully introduced trifluoroethyl thioether into the pyrimidine derivatives. Further optimization resulted in compound T7 (HNPC-A188)(5-chloro-6-(difluoromethyl)-N-(2-(2-fluoro-4-methyl-5-((2,2,2-trifluoroethyl)thio)phenoxy)ethyl)pyrimidin-4-amine). HNPC-A188 exhibits excellent acaricidal activity with LC₅₀ values of 0.19 mg/L against Tetranychus urticae, which can be compared with the commercial acaricide cyenopyrafen (LC₅₀ = 0.13 mg/L).