Two new cadinane-type sesquiterpenes from the Chinese liverwort Frullania serrata

Two new cadinane-type sesquiterpenes, frullanic acid (1) and frullanic acid methyl ester (2), together with four known bibenzyls, brittonin B (3), 3,3'-dimethoxy-4,5-methylenedioxybibenzyl (4), 3,4,5,3',4'-penlamethoxybibenzyl (5) and (±)-3-(4'-methoxybenzyl)-5,6-dimethoxyphtbalide (6), were isolated from the Chinese liverwort Frullania serrata. The structures of the new metabolites were elucidated by analysing the spectroscopic data (1D NMR, 2D NMR, HR-ESI-MS and IR). The absolute configurations of compounds 1 and 2 were determined by comparing the experimental and calculated electronic circular dichroism spectra predicted by using time-dependent density functional theory as well as the CD exciton chirality method.