A Piperine-Based Scaffold as a Novel Starting Point to Develop Inhibitors against the Potent Molecular Target Of ChtI.

The insect chitinase Of ChtI from the agricultural pest Ostrinia furnacalis (Asian corn borer) is a promising target for green insecticide design. Of ChtI is a critical chitinolytic enzyme for the cuticular chitin degradation at the stage of molting. In this study, piperine, a natural amide compound isolated from black pepper, Piper nigrum L., was discovered for the first time to have inhibitory activity toward Of ChtI. The compound-enzyme interaction was presumed to take place between the piperine benzo[ d ][1,3] dioxole skeleton and subsite -1 of the substrate-binding pocket of Of ChtI. Hence, on the basis of the deduced inhibitory mechanism and crystal structure of the substrate-binding cavity of Of ChtI, compounds 5a - f were designed and synthesized by introducing a butenolide scaffold into the lead compound piperine. The enzymatic activity assay indicated that compounds 5a - f ( K _i = 1.03-2.04 μM) exhibited approximately 40-80-fold higher inhibitory activity than the lead compound piperine ( I ) ( K _i = 81.45 μM) toward Of ChtI. The inhibitory mechanism of the piperonyl butenolide compounds was elucidated by molecular dynamics, which demonstrated that the introduced butenolide skeleton improved the binding affinity to Of ChtI. Moreover, the in vivo activity assay indicated that these compounds also displayed moderate insecticidal activity toward O. furnacalis . This work introduces the natural product piperine as a starting point for the development of novel insecticides targeting Of ChtI.