Cytotoxic Activity of Riccardin and Perrottetin Derivatives from the Liverwort Lunularia cruciata

Seven new bisbibenzyls (1-7) were isolated from the methanol extract of the liverwort Lunularia cruciata along with one previously known bibenzyl and five known bisbibenzyls. The structures of compounds 1-7 were elucidated on the basis of the spectroscopic data. These newly isolated bisbibenzyls may be divided into two groups, the acyclic bisbibenzyls, perrottetins (1-3), and the cyclic analogues, riccardins (4-7). Besides standard perrottetin and riccardin structures (1 and 4, respectively), they contain phenanthrene (3 and 5), dihydrophenanthrene (2), and quinone moieties (6 and 7), rarely found in natural products. The new compounds 3 and 5, as well as the known riccardin G, exhibited cytotoxic activity against the A549 lung Cancer cell line with IC₅₀ values of 5.0, 5.0, and 2.5 μM, respectively.