Synthesis and pesticidal activities of cyclopentanoperhydrophenanthrene 3-aryl-4,5-dihydroisoxazole-5-formate derivatives

In order to find cholesterol derivatives with high insecticidal activities, isoxazoline fragments were introduced into the C-3 position of cholesterol ( 1 ), and twenty novel cyclopentanoperhydrophenanthrene 3-aryl-4,5-dihydroisoxazole-5-formate derivatives ( Ia - It ) containing the isoxazoline fragment were prepared. Their structures were characterized by ¹H NMR, IR and HRMS. Among them, compound Ie (R = 3-Br-Ph) exhibited good insecticidal activity against Plutella xyllostella with a LC₅₀ value of 0.940 mg/mL at 48 h, which was 2.7 times of that of 1 (LC₅₀: 2.566 mg/mL). Compounds Ig (R = 3-F-Ph) and Ij (R = 4-CF₃-Ph) showed the potent aphicidal activity against Aphis citricola with LD₅₀ values of 0.042 and 0.041 μg/nymph at 48 h, respectively, which were 5.4 and 5.6 times of that of 1 (LD₅₀: 0.228 μg/nymph). The preliminary study of structure-activity relationships (SARs) indicated that introduction of the bromine atom at the C-3 position of phenyl can improve the insecticidal activity against P. xyllostella; introduction of the fluorine atom at the C-3 or C-4 position of phenyl, or introduction of the CF₃ at the C-4 position of phenyl can improve the aphicidal activity against A. citricola.