New oxylipins from Siegesbeckia glabrescens as potential antibacterial agents.

Seven rare oxylipins, siegesbeckins A–G (1 – 7) representing further bioactive constituents different from the general terpenyl compounds found in Siegesbeckia species, have been obtained from the aerial parts of Siegesbeckia glabrescens. These isolates were identified to be a series of methyl 4-methylpentanoates incorporating fatty acid moieties of different chain lengths, based on spectroscopic techniques, and their absolute configurations were determined via chemical degradation and comparison of experimental and theoretically calculated ECD spectra. With respect to bioactivity, antibacterial, anti-inflammatory and cytotoxic properties of selected compounds were evaluated. Compounds 1 and 5 showed moderate antibacterial activity against two Gram-positive bacteria with MIC values of 4.3 μg/mL, while 3 showed no pronounced activity in these assays. Unlabelled Image • Seven rare oxylipins were separated and identified from the aerial parts of Siegesbeckia glabrescens. • The absolute configurations were established via chemical degradation and analysis of ECD data. • Two compounds with shorter fatty acid chains displayed mild antibacterial activity against Gram-positive bacteria. [ABSTRACT FROM AUTHOR]