Monoterpenoid alkaloids are well known for their broad and excellent biological activities, but their extremely low content and complex chemical structure limit their practical application. This study used the biosynthetic precursor genipin as a basic material to conduct a biomimetic synthesis of iridoid alkaloids. The structures of the iridoid alkaloids were characterized by 1H and 13C NMR spectroscopy and high-resolution mass spectrometry, and their fungicidal and insecticidal activities were evaluated. Bioassay results indicated that iridoid alkaloids possess good to excellent activities against phytopathogenic fungi, diamondback moth, bean aphid, and spider mite. Compound 3s had the most promising activity against three important phytopathogenic fungi Fusarium graminearum (LC50 value of 34.5 μg/mL with a 95% confidence interval of 33.4-35.5 μg/mL), Rhizoctonia solani (18 μg/mL, 15.7-20.8 μg/mL), and Botrytis cinerea (26 μg/mL, 22.4-30.4 μg/mL), thereby emerging as a potential new fungicidal lead. The structure-activity relationship research has shown that the electrical property and steric hindrance sizes of iridoid alkaloids apparently influence fungicidal activity. Moreover, compound 3n exhibited good insecticidal activity against diamondback moth with an LC50 (35.6 μg/mL, 95% confidence interval 19.0-66.6 μg/mL) comparable to that of the commercial insecticide rotenone (35.4 μg/mL, 95% confidence interval 22.2-56.4 μg/mL). This outcome indicates that this compound deserves further study as a potential lead for development of new insecticides.
Keywords: biomimetic synthesis; fungicidal activity; insecticidal activity; iridoid alkaloids; structure−activity relationship.