Minor sesquiterpene lactones from Centaurea pullata and their antimicrobial activity.

The aerial parts of Centaurea pullata afforded, in addition to the previously isolated sesquiterpene lactones, 11beta,13-dihydrocnicin and 11beta,13-dihydro-19-desoxycnicin, three minor sesquiterpene lactones, namely, a new germacranolide, 8alpha-O-(4-acetoxy-5-hydroxyangeloyl)-11beta,13-dihydrocnicin, and two new eudesmanolides, 8alpha-O-(4-hydroxy-2-methylenebutanoyloxy)-11beta,13-dihydrosonchucarpolide and 8alpha-O-(4-hydroxy-2-methylenebutanoyloxy)-11beta,13-dihydro-4-epi-sonchucarpolide. The in vitro antimicrobial activity of all isolated sesquiterpene lactones was tested against six bacteria and eight fungal species, using a microdilution method. All compounds tested showed greater antibacterial and antifungal activities than the positive controls used.