Hookerolides A-D, the first naturally occurring C17-pseudoguaianolides from Inula hookeri

Four unprecedented C17-pseudoguaianolides with extended side chains, hookerolides A-D (1-4), were isolated from the whole plants of Inula hookeri. Their structures and absolute configurations were elucidated by a combination of NMR spectroscopy, CD spectrum, and the modified Mosher method. The in vitro bioactivity evaluation suggested that 1-4 possessed moderate to weak anti-inflammatory and cytotoxic properties.