Natural Products-Based Insecticidal Agents 1. Semisynthesis and Insecticidal Activity of 4β-Benzenesulfonamide Derivatives of Podophyllotoxin against Mythimna separata Walker

Eleven 4 beta-benzenesulfonamide derivatives of podophyllotoxin were synthesized and evaluated for insecticidal activity against the third-instar larvae of Mythimna separata Walker in vivo at the concentration of 1 mg/mL. All derivatives showed delayed insecticidal activity, which was different from the traditional neurotoxic insecticides. Compounds 4a-4f and 4i-4k were found to be more potent than podopyllotoxin in the mortality rate after 20 d against M separata. Especially compounds 4i, the corresponding final mortality rate of which was 88.9%, exhibited more potent insecticidal activity than toosendandin (81.4%), a commercial insecticide derived from Melia azedarach. Furthermore, some preliminary qualitative structure-activity relationships were also observed.