Novel bibenzyl derivatives and ent-cuparene-type sesquiterpenoids from Radula species

Four novel prenyl bibenzyls, perrottetin A–D were isolated from the liverwort Radula perrottetii together with a new sesquiterpene phenol, ent-2, 3-dihydroxycuparene and a prenyl dihydrochalcone, and their structures were determined by spectral methods and chemical transformations. Further investigation of the French species R. complanata resulted in the isolation of four new bibenzyls, 3, 4′-dimethoxybibenzyl, 3,5-dihydroxy-4-(2, 3-epoxy-3-methylbutyl)bibenzyl, radulanin H and radulanolide. R. buccinifera was chemically close to R. complanata. The composition of bibenzyls found in R. perrottetii and R. oyamensis were different from that of the other Radula species referred to in the section Radula. Some prenyl bibenzyls showed antimicrobial activity against Streptococcus aureus (20 μg/ml). The allergenic activity of R. complanata is due to (+)-frullanolide from the liverwort Frullania dilatata which is intermingled in R. complanata.