Acridone Derivatives as Photosystem II Inhibitors: Synthesis, Herbicidal Activity, and Structure-Activity

In this study, we report the synthesis of acridone derivatives and their potential as photosystem II (PSII) inhibitors, as well as their pre- and post-emergence herbicidal activities through chlorophyll a fluorescence and germination assays. Among the compounds tested for PSII activity, acridin-9(10H)-one showed the most promising results, reducing the performance index on an absorption basis and decreasing the quantum yield for electron transport compared to the control. These findings suggest an inhibitory effect on PSII within the electron transport chain. Additionally, 2-chloroacridin-9(10H)-one and 9(10H)-acridone-4-carboxylic acid exhibited respectively, leading to a reduction in radicle and hypocotyl lengths. Furthermore, we applied a molecular docking approach with the D1 protein and 4-hydroxyphenylpyruvate dioxygenase to investigate the structure-activity relationships among the acridone derivatives with these enzymes. The analysis highlighted the importance of the carbonyl group and aromatic substituents on the acridone scaffold facilitating ligand interactions, especially through hydrogen bonding. Consequently, our research group aims to optimize these molecular features to develop new, potent bioactive molecular scaffolds.