Isolation, Antiradical Activity, and Cytotoxicity of Flavonoids From Cunila angustifolia

Cunila angustifolia ("vassourinha do campo") is a plant species native to southern Brazil that is traditionally consumed as an herbal infusion. In the present study, the hydroethanolic extract of C. angustifolia leaves, its solvent-partitioned fractions, and the flavonoids acacetin and acacetin-7-O-rutinoside, reported herein for the first time in this species, were investigated for their antiradical and cytotoxic activities. Among the fractions, the ethyl acetate fraction exhibited the highest total phenolic content (633.7 mg GAE/g) and the strongest radical scavenging activity (EC₅₀: 2.0 µg/mL). Comparative evaluation of the isolated flavonoids revealed that acacetin-7-O-rutinoside displayed superior antiradical activity relative to its aglycone, suggesting that C-7 glycosylation may enhance radical scavenging capacity. Cytotoxic assays demonstrated that the crude extract was most active against MCF-7 breast cancer cells (IC₅₀: 37.2 µg/mL), while the chloroform fraction showed selective inhibitory activity against SK-Mel-28 melanoma cells (IC₅₀: 36.3 µg/mL). In contrast, the isolated flavonoids exhibited weak or selective cytotoxic effects, indicating that the biological activity of the extracts is likely attributable to synergistic interactions among multiple constituents. Overall, these findings expand the phytochemical knowledge of C. angustifolia and highlight its potential as a source of bioactive phenolic compounds.