Three New Xanthones from and Their Quorum Sensing Inhibitory Activities against .

Quorum sensing (QS) plays an important role in the production of virulence factors and pathogenicity in pathogenic bacteria and is, therefore, a hopeful target to fight against bacterial infections. During our search for natural QS inhibitors, two new xanthonolignoids ( and ), each existing as a racemic mixture, one new simple oxygenated xanthone (), and eight known analogs (-, -) were isolated from Linn. Chiral separation of yielded a pair of enantiomers and . The structures of these compounds were elucidated by spectroscopic analysis and ECD (electrostatic circular dichroism) calculations. All isolates were evaluated for their QS inhibitory activity against . Both and exhibited the most potent QS inhibitory effects with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 31.25 and 62.5 μM, respectively. Crystal violet staining was used to further evaluate the biofilm inhibition potential of compounds , and , and the formation of biofilms increased with decreasing drug concentration in a classic dose-dependent manner. The results of a cytotoxicity assay revealed that compounds , and exhibited no cytotoxic activity on PC-12 cells at the tested concentration.