Study on Design, Synthesis and Herbicidal Activity of Novel 6-Indazolyl-2-picolinic Acids.

Thirty-eight new 4-amino-3,5-dicholo-6-(1-indazolyl)-2-picolinic acids and 4-amino-3,5-dicholo-6-(2-indazolyl)-2-picolinic acids were designed by scaffold hopping and synthesized to discover potential herbicidal molecules. All the new compounds were tested to determine their inhibitory activities against and the root growth of five weeds. In general, the synthesized compounds exhibited excellent inhibition properties and showed good inhibitory effects on weed root growth. In particular, compound showed significantly greater root inhibitory activity than picloram in and Medicus at the concentration of 10 µM. The majority of compounds exhibited a 100% post-emergence herbicidal effect at 250 g/ha against and . We also found that 6-indazolyl-2-picolinic acids could induce the up-regulation of auxin genes ACS7 and NCED3, while auxin influx, efflux and auxin response factor were down-regulated, indicating that 6-indazolyl-2-picolinic acids promoted ethylene release and ABA production to cause plant death in a short period, which is different in mode from other picolinic acids.