Application of sustainable natural resources in crop protection: Podophyllotoxin-based botanical pesticides derived from Podophyllum hexandrum for controlling crop-threatening insect pests

Podophyllotoxin is isolated as a sustainable natural bioresource from the roots and rhizomes of Podophyllum hexandrum and Juniperus Sabina. In continuation of our program aimed at the discovery of biorenewable natural product-based pesticides, a series of 4 alpha-acyloxy derivatives of 2'-chloro-5-bromopicropodophyllotoxin or 2',5-dibromopicropodophyllotoxin were synthesized by structural modification of podophyllotoxin, and evaluated as insecticidal and acaricidal agents against two serious agricultural pests, Mythirnna separata Walker and Tetranychus cinnabarinus Boisduval. Among all derivatives, compounds 6a and 7a exhibited more promising insecticidal and acaricidal activities than podophyllotoxin, and the final mortality rates of 6a, 7a and 1 against M. separata (at 1 mg/mL) and T. cinnabarinus (at 0.5 mg/mL) were 50%/53.3%/36.7%, and 33%/41.8%/1.6%, respectively. This suggested that introduction of the acetoxy moiety at the C-4 position of Z-chloro-5-bromopicropodophyllotoxin/2',5-dibromopicropodophyllotoxin was necessary for the insecticidal and acaricidal activities.