Characterization of bridged guaiane-type sesquiterpenoids from Stellera chamaejasme and their antifungal activities against phytopathogenic fungi.

Plant pathogenic fungi pose a serious threat to global agricultural productivity, driving the need for novel and eco-friendly antifungal agents. An investigation into the antifungal constituents from the roots of Stellera chamaejasme led to the isolation of nine new guaiane-type sesquiterpenoids, named stelleroids D-L (1-3 and 8-13), along with eight known analogues. Their structures, featuring extensively modified bridged scaffolds and diverse oxidative patterns, were elucidated by comprehensive spectroscopic analysis and X-ray crystallography. Antifungal evaluation against five agriculturally significant phytopathogenic fungi identified compound 11 as the most potent and broad-spectrum agent, exhibiting exceptional activity against Phytophthora infestans (MIC = 3.1 μg/mL). Subsequent mechanistic studies revealed that compound 11 disrupted the cell membrane integrity of P. infestans, leading to increased permeability, leakage of cellular contents, and severe ultrastructural damage. Molecular docking simulations suggested that 11 could effectively bind to the putative targets CYP51 and SDH. Importantly, in vivo experiments on tomato fruits confirmed the significant protective and curative efficacy of 11 against late blight. This work not only expands the structural diversity of bioactive sesquiterpenoids but also provides a highly promising natural lead compound (11) with validated in planta efficacy for further development as a new antifungal agrochemical.