Discovery of triketone-quinoxaline hybrids as potent hppd inhibitors using structure-based drug design

p-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27,HPPD) belongs to the family of Fe(ll)-dependent non-heme oxygenases that occur in the majority of aerobic organisms.HPPD has proved to be a promising target in herbicide research and development.A battery of novel triketone-quinoxaline compounds has been designed using a structure-based drug design strategy and then prepared.Enzyme inhibition assays show that these synthesized derivatives possess favorable inhibition capability against Arabidopsis thaliana HPPD with IC50 values ranging from 0.317 to 0.891 μmol· L-1.Subsequently,the molecular docking results indicate that two adjacent carbonyls of the triketone moiety of the representative compound 2-(2,3-dimethyl-8-(o-tolyl)quinoxaline-6-carbo-nyl)-3-hydroxycyclohex-2-en-1-one (7d) engage in chelation with the ferrous ion of A.thaliana HPPD in a bidentate pose,and its quinoxaline scaffold forms two sets of parallel π-stacking interaction between two phenylalanine residues(Phe424 and Phe381).In addition,the extended phenyl group also interacts with Phe392 in a π-π stacking way.This study indicates that triketone-quinoxaline is a promising scaffold for discovering HPPD inhibitors with substantially increased potency,providing insight into the molecular design of new herbicides.