Wuchuyuamines A-G, seven new alkaloids isolated from the fruits of Tetradium ruticarpum and their antifungal activities

Abstract

Plant diseases caused by fungal pathogens severely threaten crop yields and food security, driving the need for new, environmentally friendly fungicides. In this study, thirty-six alkaloids, including seven novel ones (1–4, 23, 29, and 30), were isolated from the fruits of Tetradium ruticarpum, and their structures were elucidated by extensive spectroscopic analyses. The antifungal potential of compounds obtained with sufficient quantities was evaluated using the mycelial growth rate method against three phytopathogens (Alternaria solani, Bipolaris sorokiniana, and Fusarium odoratissimum). Compounds 16 and 24 showed notable activity against A. solani, exhibiting approximately 80% and 90% growth inhibition at 100 μg/mL, with IC50 values of 33.39 and 36.02 μg/mL, respectively. To evaluate the antifungal spectrum, the abundant constituents 13, 19, and 25 were further screened against sixteen phytopathogenic fungi. Among them, compound 25 displayed the most potent and broad-spectrum antifungal activity, achieving an IC50 of 13.15 μg/mL against Fusarium graminearum, which was stronger than the positive control hymexazol. Furthermore, SEM and TEM analyses revealed that compound 25 markedly disrupted the surface morphology and cellular ultrastructure, suggesting a potential link to membrane integrity impairment. Additionally, leakage assays showed increased release of nucleic acids and proteins, providing evidence that compound 25 increased membrane permeability and compromised the membrane integrity in F. graminearum. Therefore, compound 25 represents a promising lead structure for the development of novel, eco-friendly fungicides.