Synthesis of Quaternary Ammonium Derivatives of Eugenol and Their Antifungal Mechanism against <i>Gloeophyllum trabeum</i> Wood-Decaying Fungi

To discover novel preservatives for treating wood-decaying fungi, 48 novel eugenol quaternary ammonium salt derivatives were designed and synthesized. Among them, compounds <b>3j</b>, <b>3k</b>, <b>4j</b>, <b>4k</b>, <b>5j</b>, <b>5k</b>, and <b>6j</b> showed remarkable antifungal activity against <i>Gloeophyllum trabeum</i> (<i>G. trabeum</i>), affording EC₅₀ values ranging from 2.11-7.50 μg/mL. Notably, <b>3j</b> demonstrated the most potent activity against <i>G. trabeum</i> (EC₅₀ = 0.14 μg/mL), surpassing the positive control dodecyldimethylbenzylammonium chloride (DDBAC, EC₅₀ = 3.33 μg/mL). Additionally, <b>3j</b> significantly reduced wood mass loss and decay caused by <i>G. trabeum</i>. Mechanistic studies revealed that <b>3j</b> disrupted the fungal ultrastructure, increased membrane permeability, and induced cellular leakage. Furthermore, <b>3j</b> disrupted the antioxidant system and energy metabolism, resulting in the accumulation of reactive oxygen species. The multiomics data revealed the molecular mechanisms by which <b>3j</b> regulated <i>G. trabeum</i>, including key genes, proteins, metabolites, and pathways. This study elucidates key mechanistic insights into developing a natural-product-derived wood preservative.