Sesquiterpene lactones from Polydora serratuloides and their quorum sensing inhibitory activity

The leaves of Polydora serratuloides, with the synonym Vernonia perrottetii are widely used as purgative agents for gastrointestinal problems, and other members of Vernonieae have been used in African traditional medicine for decades. A new sesquiterpene lactone of the keto-hirsutinolide type, 13-acetoxy-1(4β),5(6)β-diepoxy-8α-(senecioyloxy)-3-oxo-1,7(11)-germacradiene-12,6-olide 1, was isolated from the hexane extract of its leaves, in addition to the known 13-acetoxy-1,4β-epoxy-8α-(senecioyloxy)-3-oxo-1,5,7(11)-germacratriene-12,6-olide 2. Three common flavonoids (apigenin 3, luteolin 4 and velutin 5) were also isolated. The antibacterial and quorum sensing inhibitory activities of compounds 1 and 2 and crudes extracts showed limited activity on Bacillus subtilis and Staphylococcus aureus, with no activity on Gram negative bacteria. However, quorum sensing (QSI) experiments indicated that 1 and 2, and the four crude extracts had interesting inhibitory activity on the biosensor organism, Chromobacterium violaceum ATCC 12472 in the range of 0.33-5.25 mg mL^-1, with compound 1 being the most effective at 0.33 mg mL^-1.