Molecular Aspects of Tannin-Anthelmintic Interactions as Revealed by NMR Spectroscopy.

The interactions between plant polyphenols and commercial anthelmintics remain largely unexplored, despite the benefits of understanding these interactions for mitigating anthelmintic resistance. This study investigated the interactions of flavan-3-ols, dimeric proanthocyanidins, and selected hydrolyzable tannins with two anthelmintics, ivermectin (IVM) and thiabendazole (TBZ), at various polyphenol to anthelmintic molar ratios using nuclear magnetic resonance (NMR) spectroscopy. Chemical shift changes (Δs), indicating interaction, were observed for specific regions of the compounds and at all polyphenol to anthelmintic molar ratios. For IVM interactions with polyphenols, downfield Δs were observed and were primarily associated with hydroxyl groups within the structures of the anthelmintic and polyphenols, suggesting that the interactions involved hydrogen bond formation. For TBZ interactions with polyphenols, however, both upfield and downfield Δs were observed, suggesting that both hydrogen bonding and hydrophobic interactions were involved. All of the studied polyphenols interacted more strongly with TBZ than with IVM.