Bibenzyl-Based Meroterpenoid Enantiomers from the Chinese LiverwortRadula sumatrana

Six new pairs of bibenzyl-based meroterpenoid enantiomers, (±)-rasumatranin A–D ( 1 – 4 ) and (±)-radulanin M and N ( 5 and 6 ), and six known compounds were isolated from the adnascent Chinese liverwort, Radula sumatrana. Their structures were elucidated based on spectroscopic data and chiral phase HPLC-ECD analyses. The structures of 1 and 7 were also confirmed by single-crystal X-ray diffraction analysis. Cytotoxicity tests of the isolated compounds showed that 6-hydroxy-3-methyl-8-phenylethylbenzo[ b ]oxepin-5-one ( 8 ) showed activity against the human cancer cell lines MCF-7, PC-3, and SMMC-7721, with IC 50 values of 3.86, 6.60, and 3.58 μM, respectively, and induced MCF-7 cell death through a mitochondria-mediated apoptosis pathway.