Membrane-Active Phenolic Compounds from Cephalaria uralensis (Murray) Roem. & Schult.: Isolation, Structural Characterization, and Antioxidant Potential

In this study, we isolated and identified six major phenolic constituents from Cephalaria uralensis. The compounds—quercetin 6-C-β-glucopyranoside, isoorientin, swertiajaponin, 3,5-dicaffeoylquinic acid, 4,5-dicaffeoylquinic acid, and chlorogenic acid—were characterized by LC–MS and NMR. All isolates exhibited strong free-radical scavenging ability and significant interaction with lipid monolayers (Δπ up to ~6.5–7 mN/m), suggesting dual antioxidant and membrane-perturbing activities. In antioxidant assays, isoorientin, showed the lowest IC50 among the isolates. Notably, 4,5-dicaffeoylquinic acid caused the largest increase in monolayer surface pressure, indicating a particularly strong tendency to integrate with lipid bilayers. In fact, chlorogenic acid, isoorientin, and swertiajaponin are well-documented natural antioxidants, and related phenolic acids have been shown to possess potent antimicrobial activity. Thus, the C. uralensis phenolics identified in our study likely underlie the extract’s bioactivity. These findings highlight C. uralensis as a source of membrane-active polyphenols with potential applications in skin-related oxidative and microbial conditions.