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

In this work, several imidazo[1,2-a]pyridines were synthesized through the Groebke-Blackburn-Bienaymé three-component reaction (GBB-3CR), and their phytotoxicity was evaluated in vitro by the influence on the growth of wheat coleoptiles and three important agricultural seeds (Allium cepa, Lactuca sativa, and Solanum lycopersicum) 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 ortho 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-a]pyridine-tetrazole hybrids, which were also evaluated in these bioassays. The phytotoxicity on seed germination and growth bioassays demonstrated that A. cepa was the most susceptible seed, and the most affected parameters were the root and shoot lengths. The most active compound was also evaluated against Bidens pilosa, Urochloa decumbens, and Panicum maximum 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.