Novel Inhibitors of an Insect Pest Chitinase: Design and Optimization of 9-O-Aromatic and Heterocyclic Esters of Berberine

OfChi-h, a lepidopteran-exclusive glycoside hydrolase family 18 (GH18) chitinase from the agricultural insect pest Ostrinia furnacalis, is a promising molecular target candidate for pest control and management. Berberine (BER), a traditional Chinese medicine, binds to a wide variety of glycosyl hydrolases via an identical mechanism, showing potential as a pesticide lead compound. In this work, we found that BER was a moderate inhibitor of OfChi-h with a Ki of 16.1 μM. To improve its efficacy, a series of BER derivatives featuring an ester bond linked to an aromatic or heterocyclic aromatic ring at the 9-position were designed and evaluated as effective OfChi-h inhibitors. The most potent compound, compound 19e with a nicotinate group, exhibited a Ki of 0.093 μM. Molecular docking analysis suggested that the common binding mode of BER derivatives featured a network of π-πstacking and electrostatic interactions and that the group at the 9-position enhanced the van der Waals and hydrogen bonding interactions. Administration of the BER derivative 19c to 4th-instar O. furnacalis larvae in an artificial diet led to their impaired growth and metamorphosis. This work provides a new starting point for the modification of BER for use in pest control.