Structure Characterization and Antibacterial, Antifungal, and Antiquorum-Sensing Activity of New Metabolites From the Lipophilic Fractions of Platycodon grandiflorum Root.

The root of Platycodon grandiflorum has long been used as a vegetable and traditional medicine. Although the antibacterial activity of the plant's lipophilic (hexanes and dichloromethane) fractions has been reported, the specific antibacterial compounds have not been identified. In this study, chemical analysis of the lipophilic fractions of P. grandiflorum extracts led to the discovery of five new polyacetylenes (1-5) and nine known compounds (6-14). Their structures were elucidated and confirmed based on 1D and 2D NMR data together with mass spectra. In particular, the relative and absolute configurations of 1 were elucidated by coupling constants, NOESY and J-based configurational analysis in combination with Mosher's method. Compounds 1 and 2 demonstrated strong antifungal activity against Candida albicans. Additionally, compound 1 significantly inhibited quorum sensing in Chromobacterium violaceum, a commonly used biosensor strain. Compounds 2 and 14 also exhibited mild inhibitory activity. Compounds 8 and 12-14 exhibited potent antibacterial activity against Escherichia coli, Kocuria rhizophila, and Staphylococcus aureus, as well as antifungal activity against Candida albicans. These compounds may be responsible of the antimicrobial activity of P. grandiflorum.