Artemselenoids A-H, eight guaiane-type sesquiterpenoid dimers from and their antihepatoma activities.

Eight undescribed guaiane-type sesquiterpenoid dimers (GSDs), artemselenoids A-H (1-8), together with nine known GSDs (9-17), were isolated from . Their structures and absolute configurations were determined through comprehensive spectral analyses, theoretical ECD calculations, and NMR computations. Chemically, compound 1 represented the first example of two guaianolide lactone units dimerizing through unprecedented C-3-C-11' and C-4-C-13' bonds a [2 + 2] cycloaddition reaction and producing a structurally unique 5,4 spirocyclic system; compounds 2-8 were biogenetically formed through a [4 + 2] cycloaddition reaction.