Discovery of flavonoids with quorum sensing inhibitory activity from Hymenocallis littoralis

Hymenocallis littoralis (Jacq.) Salisb. was a traditional folk medicinal herb used externally in China. The chemical constituents and their bioactivity of the H. littoralis was investigated in our study. Hymevanes A (1) and B (2), two new flavanes, together with seven known compounds (3-9), were isolated from H. littoralis. The structures of these compounds were determined through comprehensive NMR spectroscopic data, HRESIMS and ECD comparison. Among the known compounds, three known compounds were isolated for the first time from this plant, including tazettone A (3), (2S)-7,4'-dihydroxy-8-methylflavan (5), and (S)-liquiritigenin (7). Significantly, compound 4 was the first reported flavane as quorum sensing inhibitor of Pseudomonas aeruginosa and has been identified as a safe antibacterial agent that synergized with ceftazidime and imipenem and inhibited biofilm formation, that might act through competitively binding to quorum sensing receptors. Based on the present results, compound 4 may be potential antibacterial agent.