Acaricidal and insecticidal efficacy of new esters derivatives of a natural coumarin osthole

To discover non-food bioactive natural-product-based pesticides for crop protection, new osthole esters ((2′E)− 4′-(isoxazolin-5''-yl)carbonyloxyosthole derivatives) containing the isoxazoline fragment were constructed by structural modification of a natural coumarin osthole isolated from Cnidium monnieri. The configurations of three compounds were confirmed by X-ray crystallography. Their agricultural activities were evaluated against two typically crop-threatening pests Mythimna separata Walker and Tetranychus cinnabarinus Boisduval. Against T. cinnabarinus, compounds 4 (LC50: 0.75 mg/mL) and 5h (LC50: 0.76 mg/mL) displayed ≥ 1.5-fold acaricidal activity of osthole and good control effects in the greenhouse. Against M. separata, compounds 5a (final mortality rate (FMR): 55.1%), 5c (FMR: 62.0%), and 5o (FMR: 55.1%) at 1 mg/mL showed 1.5–1.6 folds growth inhibitory activity of osthole. It suggested that introduction of the acryloyloxy group at the C-4′ position of osthole was important for insecticidal and acaricidal activities, and compound 4 can be further structurally modified as pesticidal agents.