Detoxification Mechanism of Hinokitiol by <i>Alternaria alternata</i> and Its Application in Agricultural Antifungal Control

<i>Alternaria alternata</i> is a common plant pathogen that can infect crops and reduce their production. In this work, an antagonism experiment between <i>A. alternata</i> and the essential oil of arborvitae (<i>Platycladus orientalis</i>) was performed, and it was proven that <i>A. alternata</i> had developed resistance to this plant-derived fungicide. <i>A. alternata</i> facilitated the biotransformation of hinokitiol (<b>1</b>), the main antifungal compound in the essential oil of arborvitae, into (<i>R</i>)-2-hydroxy-β-methylbenzeneethanol (<b>2</b>), which does not have antifungal activity against <i>A. alternata</i>. This biotransformation is an unusual ring-contraction reaction that was verified to be catalyzed by P450 enzyme hydroxylation and Baeyer-Villiger oxidation. In addition, the P450 enzyme inhibitors 1-aminobenzotriazole and piperonyl butoxide effectively prevented the destruction of the hinokitiol structure by <i>A. alternata</i>, and the combined use of these P450 enzyme inhibitors significantly increased the antifungal activity of hinokitiol. This work provides a theoretical reference for the further development of botanical fungicides.