Pinonic Acid Derivatives Containing Thiourea Motif:\nPromising Antifungal Lead Compound Targeting Cellular Barrier of Colletotrichum fructicola

In order to explore novel antifungal\nlead compounds from plant\nessential oil, thirty-two pinonic acid derivatives containing thiourea\ngroups were designed and synthesized using α-pinene as a raw\nmaterial. One of these pinonic acid derivatives compound <b>3a</b> exhibited noteworthy <i>in vitro</i> antifungal activity\nagainst Colletotrichum fructicola (EC<sub>50</sub> = 9.22 mg/L), which was comparable to that of the positive\ncontrol kresoxim-methyl (EC<sub>50</sub> = 9.69 mg/L). Structure–activity\nrelationship (SAR) studies demonstrated that the introduction of thiourea\ngroups, F atoms, and Cl atoms into the structure of pinonic acid derivatives\nsignificantly improved their antifungal activity. The <i>in vivo</i> antifungal test revealed that compound <b>3a</b> could effectively\ncontrol pear anthracnose. It also proved that compound <b>3a</b> showed low acute oral toxicity to honeybees (LD<sub>50</sub> >\n100\nμg/bee) and low or no cytotoxicity to LO2 and HEK293 cell lines.\nThe preliminary mechanism of action studies revealed that compound <b>3a</b> caused mycelium deformity, increased cell membrane permeability,\nblocked the normal process of phospholipase C on the cell membrane,\nand reduced mycelium protein content. The results of molecular docking\nstudies demonstrated the stable binding of compound <b>3a</b> to phospholipase C and chitin synthetase. This study suggested that\ncompound <b>3a</b> could be used as a promising lead compound\nfor the development of novel antifungal agents targeting the cellular\nbarrier of C. fructicola.