Combinatorial Synthesis of A Series of Alkyl/Alkenylacyloxy Derivatives at the C-28 Position of Toosendanin as Insecticidal Agents

In continuation of our program aimed at the discovery and development of natural-product-based insecticidal agents, we have synthesized eighteen alkyl/alkenylacyloxy derivatives at the C-28 position adopting exo-configuration of toosendanin (3a-r) by the reaction of toosendanin with fatty acids in the presence of N,N'-diisopropylcarbodiimide and 4- dimethylaminopyridine. Their activity was preliminarily evaluated against the pre-third-instar larvae of Mythimna separata Walker in vivo. Especially compounds 3e and 3o displayed the more promising insecticidal activity than their natural precursor, toosendanin. It suggested that for the n-alkyloyloxy series derivatives, the proper length of the side chain R at the C-28 position of toosendanin was very important for their insecticidal activity.