Comparative Analysis of the Toxicity of 1,10-Phenanthroline, 4-Methoxybenzaldehyde, and Phenylphenols (2-, 3-, and 4-Phenylphenol) Against Trichostrongylus colubriformis as a Parasitic Nematode and Caenorhabditis elegans as a Free-Living Model

Gastrointestinal nematode infections pose a significant challenge to ruminant health and productivity, highlighting the need to identify novel compounds with anthelmintic activity. In this study, the larvicidal activities of 1,10-phenanthroline, 4-methoxybenzaldehyde, and the regioisomers 2-, 3-, and 4-phenylphenol were comparatively evaluated against ensheathed and exsheathed third-stage larvae (L3) of Trichostrongylus colubriformis and Caenorhabditis elegans. In T. colubriformis, all compounds except 3-phenylphenol induced significant larval mortality, with 1,10-phenanthroline exhibiting the highest activity, followed by 4-methoxybenzaldehyde, 4-phenylphenol, and 2-phenylphenol. In C. elegans, all compounds exhibited significant activity, with 1,10-phenanthroline again showing the highest activity, while the remaining compounds followed the order: 4-phenylphenol > 3-phenylphenol > 2-phenylphenol > 4-methoxybenzaldehyde. Differences in susceptibility between the two species suggest that structural and species-specific factors may influence the activity of these compounds. Overall, these findings identify chemical structures with in vitro activity against parasitic nematodes and provide a basis for further investigation of their anthelmintic potential.