Preparation and Herbicidal Activity of Halogenated 8-Hydroxyquinoline-2-carboxanilides

In this study a series of twelve ring-substituted 8-hydroxyquinoline-2-carboxanilides was prepared and characterized. The discussed compounds were synthesized by using microwave-assisted synthesis. The compounds were tested for their activity related to inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. The compounds were found to inhibit PET in photosystem II. Significant PET-inhibiting activity was observed for meta-substituted compounds showing IC₅₀ values close to that of photosystem II herbicide DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea, IC₅₀ = 1.9 μmol/L). N-(3-Fluorophenyl)-8-hydroxyquinoline-2-carboxamide showed the highest PET inhibition. The activity of meta- and para-substituted compounds decreased with lipophilicity increase and electron-withdrawing effect. No influence of any of these parameters on PET-inhibiting activity of ortho-substituted compounds was observed.