Plant natural product-based pesticides in crop protection: semi-synthesis, mono-crystal structures and agrochemical activities of osthole ester derivatives, and study of their toxicology against Tetranychus cinnabarinus (Boisduval).

Abstract

Owing to large amounts of synthetic pesticides being extensively and unreasonably used for crop protection, currently, resistance and negative impacts on human health and environment safety have appeared. Therefore, development of potential pesticide candidates is highly urgent. Herein, a series of ester derivatives of osthole were designed and synthesized as pesticidal agents. Six spatial configurations of 4'-(p-toluenoyloxy)osthole (4b), 4'-(m-fluorobenzoyloxy)osthole (4f), 4'-(p-fluorophenylacetyloxy)osthole (4m), 4'-(3'',4''-methylenedioxybenzoyloxy)osthole (4q), 4'-formyloxyosthole (4u) and 4'-acetyloxyosthole (4v) were determined by X-ray mono-crystal diffraction. Compounds 4b, 4'-(p-chlorobenzoyloxy)osthole (4g), 4'-(m-chlorobenzoyloxy)osthole (4h), 4'-(p-bromobenzoyloxy)osthole (4i) and 4'-(2''-chloropyridin-3''-ylcarbonyloxy)osthole (4p) showed higher insecticidal activity than toosendanin against Mythimna separata Walker; notably, compound 4b displayed 1.8 times insecticidal activity of the precursor osthole. Against Tetranychus cinnabarinus Boisduval, compounds 4g and 4h showed 3.3 and 2.6 times acaricidal activity of osthole, and good control effects in the glasshouse. Scanning electron microscopy assay demonstrated that compound 4g can damage the cuticle layer of T. cinnabarinus resulting in death. Compounds 4g and 4h can be further studied as lead pesticidal agents for the management of M. separata and T. cinnabarinus. These results will pave the way for application of osthole derivatives as agrochemicals. © 2024 Society of Chemical Industry.