Antifungal alkaloids from the branch‐leaves of Clausena lansium Lour. Skeels (Rutaceae)

BACKGROUND The rational utilization of botanical secondary metabolites is one of the strategies to reduce the application of chemical fungicides. The extensive biological activities of Clausena lansium indicate that it has the potential to develop botanical fungicides. RESULTS A systematic investigation on the antifungal alkaloids from C. lansium branch‐leaves following bioassay‐guided isolation was implemented. Sixteen alkaloids, including two new and nine known carbazole alkaloids, one known quinoline alkaloid and four known amides, were isolated. Compounds 4, 7, 12 and 14 showed strong antifungal activity on Phytophthora capsiciwith EC50 values ranging from 50.67 to 70.82 μg mL−1. Compounds 1, 3, 8, 10, 11, 12 and 16 displayed different degrees of antifungal activity against Botryosphaeria dothidea with EC50 values ranging from 54.18 to 129.83 μg mL−1. It was reported for the first time that these alkaloids had antifungal effects on P. capsici or B. dothidea, and their structure–activity relationships were further discussed systematically. Additionally, among all alkaloids, dictamine (12) had the strongest antifungal activities against P. capsici (EC50 = 50.67 μg mL−1) and B. dothidea (EC50 = 54.18 μg mL−1), and its physiological effects on P. capsici and B. dothidea also were further evaluated. CONCLUSION Capsicum lansium is a potential source of antifungal alkaloids, and C. lansium alkaloids had the potential as lead compounds of botanical fungicides in the development of new fungicides with novel action mechanism. © 2023 Society of Chemical Industry. Sixteen antifungal alkaloids were isolated from C. lansium following the bioassay‐guided, and their structure‐activity relationships were discussed.