Phytotoxicity Study of (Amino)imidazo[1,2‑<i>a</i>]pyridine Derivatives Toward the Control of Bidens\npilosa, Urochloa decumbens, and Panicum maximum Weeds

In this work, several\nimidazo[1,2-<i>a</i>]pyridines\nwere synthesized through the Groebke–Blackburn–Bienaymé\nthree-component reaction (GBB-3CR), and their phytotoxicity was evaluated <i>in vitro</i> by the influence on the growth of wheat coleoptiles\nand three important agricultural seeds (Allium cepa, Lactuca sativa, and Solanum lycopersicum) at test concentrations of 1000,\n300, 100, 30, and 10 μM. A structure–activity relationship\nwas established, showing the importance of halogen groups at the <i>ortho</i> position of the attached aromatic ring and the presence\nof a cyclohexylamine group for greater activity. Post-modification\nof some GBB-3CR adducts was carried out, leading to imidazo[1,2-<i>a</i>]pyridine-tetrazole hybrids, which were also evaluated\nin these bioassays. The phytotoxicity on seed germination and growth\nbioassays demonstrated that <i>A. cepa</i> was the most\nsusceptible seed, and the most affected parameters were the root and\nshoot lengths. The most active compound was also evaluated against Bidens pilosa, Urochloa decumbens, and Panicum maximum weeds under\nhydroponic conditions to assess its phytotoxic potential at a more\nadvanced level of bioassays. Promising results were also achieved,\nin which the most affected growth factor by inhibition was the root\ngrowth, and a stimulus to shoot growth was noted, making it a promising\nhit in the search for new herbicides.