Nematicidal activity of multi‐halogenated indoles against <scp> <i>Caenorhabditis elegans</i> </scp>

Abstract BACKGROUND Plant‐parasitic nematodes (PPN) cause annual crop losses exceeding US$157 billion worldwide, and escalating resistance to conventional nematicides demands novel chemical scaffolds. Although indole derivatives exhibit broad‐spectrum bioactivity, the nematicidal potential of multi‐halogenated indoles remains underexplored. This study evaluates 50 halogen‐substituted indoles for nematicidal activity using Caenorhabditis elegans as a proxy nematode model, with mechanistic investigation through phenotypic, in vitro , and in silico approaches. RESULTS Fifty multi‐halogenated indoles were screened for nematicidal activity. Particularly, 4,5‐dichloroindole (45DCI), 4,6‐dibromoindole (46DBI), and 4,6‐dichloroindole (46DCI) displayed rapid and potent nematicidal effects in C. elegans , with an LC 95 value of 6 μg mL −1 . The best hit compound, 45DCI, reduced locomotion from 13 to 8 thrashes per min at 3 μg mL −1 , egg‐hatching rates to 31% at 6 μg mL −1 , and larval progression by 85% at 4 μg mL −1 . 45DCI markedly elevated intracellular reactive oxygen species (ROS) and lipofuscin accumulation, indicating accelerated aging. Molecular docking analysis predicted strong binding interactions with glutathione S ‐transferase‐5 (GST‐5), a key enzyme in oxidative stress response in C. elegans . The QSAR analysis indicated that the halogen substitution at the C4, C5, C6, and C7 positions of the indole ring increases nematicidal potency. CONCLUSION Di‐halogenated indoles, particularly C4/C6‐substituted derivatives, exhibit potent multi‐stage nematicidal activity in the free‐living model nematode C. elegans , disrupting locomotion, development, and stress tolerance through ROS induction. While molecular docking indicates a potential mechanism via GST‐5 inhibition, experimental validation is required to conclusively establish this mode of action. These findings provide preliminary evidence supporting further evaluation of di‐halogenated indoles against PPN species. © 2026 Society of Chemical Industry.