Antifungal and Allelopathic Activities of Sesquiterpenes from Solidago canadensis

One new eudesmane sesquiterpene 1 and one new chromolaevane sesquiterpene 2, along with 19 known compounds, have been isolated from the invasive plant Solidago canadensis. Their structures were established by spectroscopic means, including 1D/2D-NMR and HR-ESIMS analyses. Compounds 10 and 12, in combination with fluconazole, showed significant activity in an in vitro synergistic antifungal assay against Candida albicans, with FIC values of <0.15625 and <0.28125, respectively. Meanwhile, the allelopathic effects of these sesquiterpenes on Arabidopsis seed germination were also tested. Compounds 5, 7, 17 and 18 retarded the seed germination of Arabidopsis with IC50 values ranging from 9.1 to 41 μg/mL, while other compounds showed no obvious inhibitory effects.