Systematic Study on Turpentine-Derived Amides from Natural Plant Monoterpenes as Potential Antifungal Candidates

To overcome the high volatility, low aqueous solubility, and few definite action sites of monoterpenoid pesticides and improve their properties and effectiveness in the control of crop pathogenic fungi, herein, a series of natural turpentine-based amide derivatives exhibiting satisfactory antifungal activity were designed and synthesized. A systematic study was conducted on antifungal activity and the physiological and biochemical response of compounds 5o (EC50 = 1.139 μg/mL) and 5j (EC50 = 1.762 μg/mL) against Rhizoctonia solani. The effect of the target compound on the potential target-site succinate dehydrogenase was evaluated. The soluble concentrates of compounds 5o and 5j possessing good performance and control effects were prepared for practical application. To conduct a comprehensive analysis of the relationship between structural descriptors and activity, four representative title compounds were selected for theoretical calculation: 5o, 5j, 5k, and 5j. The binding mode of compound 5o and boscalid with succinate dehydrogenase was analyzed via molecular docking. This study provides a reference for the development of monoterpene pesticides with high efficiency, elucidated target sites, and the appropriate formula.