Iodine-catalyzed oxidative cyclisation for the synthesis of sarisan analogues containing 1,3,4-oxadiazole as insecticidal agents

Abstract

In continuation of our research aimed at the discovery and development of natural products-based insecticidal agents, a series of novel sarisan analogues containing 1,3,4-oxadiazole through iodine-catalyzed oxidative cyclisation were prepared as insecticidal agents against the pre-third Mythimna separata Walker at 1 mg mL⁻¹ in vivo. Compound 8r, 8t, 8k and 8q exhibited more promising insecticidal activities with final mortality rates of >60%, when compared with sarisan and toosendanin (a commercial insecticide). An efficient way using iodine as the catalyst and K₂CO₃ as base for the synthesis sarisan analogues containing 1,3,4-oxadiazole was developed. The results revealed that introduction of fluorophenyl or 4-cyanophenyl units on the 1,3,4-oxadiazole ring at the C-3 position of sarisan could afford more potent compounds. Moreover, introduction of heteroaromatic fragments on the 1,3,4-oxadiazole ring at the C-3 position of sarisan was very crucial for the insecticidal activity.