Artemselenoids A–H, eight guaiane-type sesquiterpenoid dimers from Artemisia selengensis 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 Artemisia selengensis. 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 via 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. Specifically, compounds 2–7 were connected by C-1–C-13′ and C-4–C-11′ bonds, while compound 8 was linked by C-1–C-13′ and C-4–C-11′ bonds. Antihepatoma assays indicated that the most active compounds 3 and 8 demonstrated significant inhibitory effects on three hepatoma cell lines, with IC₅₀ values of 7.4 and 5.1 μM (HepG2), 5.9 and 8.6 μM (Huh7), and 20.9 and 9.6 μM (SK-Hep-1), which were equal to those of the positive control sorafenib.