Five new sesquiterpenoids, britannitins D-H (1-5) were isolated from P. britannicum together with nine known compounds (6-14). Comprehensive spectroscopic analyses, including 1D and 2D NMR techniques, were employed to elucidate the structures of all new compounds. Compound 1 was a novel eucalyptane-type sesquiterpenoid generated via cleavage at C-2/C-3 followed by hydrolytic opening of the 12,8-lactone ring. Compounds 2, 5-8, and 10-12 were evaluated for cytotoxic activity against five cancer cell lines. Compounds 5, 6 and 12 displayed moderate cytotoxicity in cell lines at a concentration of 10 μmol/L.
Zhang et al. (Wed,) studied this question.