Cytotoxic sesquiterpenoid dimers from the resin of Commiphora myrrha Engl

Seven undescribed sesquiterpenoid dimers, commiphomyrones A - G, together with three known analogs, were isolated from the resin of Commiphora myrrha Engl.. The structures of the undescribed compounds were elucidated based on a comprehensive analysis of spectroscopic data (NMR, UV, IR, and MS), and the absolute configurations were defined by comparing the experimental and calculated ECD spectra as well as by performing X-ray crystallographic analysis. All the isolated dimeric sesquiterpenoids feature a 7-oxabicyclo [2.2.1] hept-2-ene moiety formed by the [4 + 2] cycloaddition of two sesquiterpenoids. Commiphomyrones C and G and commiphoratone D showed cytotoxic activity against the HGC-27 cell line with IC₅₀ values of 22.76, 25.01, and 27.51 μM, respectively.