Cembrane-Type Diterpenoids from the Chinese Liverworts <i>Chandonanthus hirtellus</i> and <i>C. birmensis</i>

Six new cembrane-type diterpenoids (1–6) were isolated from two species of Chandonanthus: Chandonanones A, B, and D–F (1, 2, and 4–6) were isolated from C. hirtellus, and chandonanones B, C, E, and F (2, 3, 5, and 6) from C. birmensis. Five known diterpenoids, (8E)-4α-acetoxy-12α,13α-epoxycembra-1­(15),8-diene (7), isochandonanthone (8), chandonanthone (9), anadensin (10), and 2,10,14-triacetoxy-7,8,18,19-diepoxydolabell-3­(E)-ene (11), were also obtained. The structures of the new metabolites were established by analyses of their spectroscopic data (1D NMR, 2D NMR, HRESIMS, and IR). The absolute configurations of compounds 1 and 2 were unequivocally confirmed using single-crystal X-ray diffraction analysis with Cu Kα radiation. Cytotoxicity tests of the isolated diterpenoids against seven cancer cell lines (DU145, PC3, A549, PC12, NCI-H292, NCI-H1299, and A172) revealed that some of the diterpenoids had weak activity.