Herbicidal Potential of Diarylamines Derived from Anthranilic Acid

Efforts to develop new herbicides are urgent due to various challenges, such as the growing prevalence of herbicide-resistant weed species. Synthetic anthranilates act as plant growth modulators and exhibit phytotoxic potential. This study investigated the phytotoxic activity of twenty-two synthetic diarylamines derived from anthranilic acid. Bioassays were conducted at concentrations of 1000, 500, and 100 µmol L–1 to evaluate the early growth of two eudicotyledonous species, lettuce (Lactuca sativa L.) and wild radish (Raphanus raphanistrum L.), as well as one monocotyledonous species, sourgrass (Digitaria insularis (L.) Fedde). In addition, physicochemical descriptors were analyzed as complementary parameters to aid the interpretation of the compounds' phytotoxic profiles. The four most phytotoxic compounds were further evaluated for their ecotoxicity in zooplankton. Within all tested compounds, nine diarylamines (1, 2, 3, 4, 5, 19, 20, 21, and 22) demonstrated significant inhibitory activity on the early growth of target plant species, particularly at the highest concentration tested (1000 µmol L–1), when compared to the solvent control. Physicochemical property analysis indicated that these compounds share structural features with commercial herbicides, which may be relevant for the discovery of new herbicidal agents. Among them, diarylamines 1–4, which feature an unsubstituted anthranilic acid moiety (A ring) connected to a mono- or di-methoxylated aromatic ring (B ring), showed the strongest inhibitory effects in weed growth bioassays. Nevertheless, zooplankton ecotoxicity assays showed no significant adverse effects from these four compounds on zooplankton richness and abundance. Therefore, diarylamines derived from anthranilic acid exhibit herbicidal potential, although further studies are required to clarify their mechanisms of action and to better assess their environmental behavior under different exposure conditions.