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

In this work, several imidazo[1,2-<i>a</i>]pyridines were synthesized through the Groebke-Blackburn-Bienaymé three-component reaction (GBB-3CR), and their phytotoxicity was evaluated <i>in vitro</i> by the influence on the growth of wheat coleoptiles and three important agricultural seeds (<i>Allium cepa</i>, <i>Lactuca sativa</i>, and <i>Solanum lycopersicum</i>) at test concentrations of 1000, 300, 100, 30, and 10 μM. A structure-activity relationship was established, showing the importance of halogen groups at the <i>ortho</i> position of the attached aromatic ring and the presence of a cyclohexylamine group for greater activity. Post-modification of some GBB-3CR adducts was carried out, leading to imidazo[1,2-<i>a</i>]pyridine-tetrazole hybrids, which were also evaluated in these bioassays. The phytotoxicity on seed germination and growth bioassays demonstrated that <i>A. cepa</i> was the most susceptible seed, and the most affected parameters were the root and shoot lengths. The most active compound was also evaluated against <i>Bidens pilosa</i>, <i>Urochloa decumbens</i>, and <i>Panicum maximum</i> weeds under hydroponic conditions to assess its phytotoxic potential at a more advanced level of bioassays. Promising results were also achieved, in which the most affected growth factor by inhibition was the root growth, and a stimulus to shoot growth was noted, making it a promising hit in the search for new herbicides.