Design, Synthesis,and Herbicidal Evaluation of NovelSynthetic Auxin Herbicides Containing 6‑Indolylpyridine OximeEster/Amine

In this study, a series of 6-indolylpyridine oxime ester/amide derivatives were synthesized as novel synthetic auxin herbicides (SAHs) for postemergence herbicidal applications. At 30 g ai/ha, compounds <b>9q</b>, <b>9u</b>, <b>9v</b> and <b>9w</b> demonstrated inhibition rates of 90 to 100% against weeds Echinochloa crus-galli (<i>EC</i>) and Digitaria sanguinalis (<i>DS</i>). Even at a reduced 7.5 g ai/ha, these compounds maintained over 90% inhibition against four broadleaf weeds, with effects comparable to those of commercial herbicides halauxifen-methyl (HAM), indolauxipyr (IND) and indolauxipyr-cyanomethyl (INC). Crop sensitivity tests confirmed the suitability of compounds <b>9w</b> and <b>9u</b> for application in wheat and rice fields at 30 g ai/ha. Molecular docking analysis revealed that compound <b>9w</b> formed significant hydrogen bonding and π–π stacking interactions with key amino acid residues. Additionally, half maximal inhibitory concentration (IC₅₀) values of compounds <b>9u</b> and <b>9w</b> for IAA <i>in vitro</i> inhibition activity were 6.153 and 4.389 μM, respectively, outperforming HAM (9.061 μM). Compounds <b>9u</b> and <b>9w</b> show promising potential as lead candidates for novel SAHs.