Diverse Prenylated Bibenzyl Enantiomers from the Chinese Liverwort Radula apiculata and Their Cytotoxic Activities

An EtOH extract of the Chinese liverwort Radula apiculata showed cytotoxic activity against the A549 lung Cancer cell line. Bioassay-guided fractionation led to the isolation of 19 prenylated bibenzyls, including eight previously unknown dimeric prenylated bibenzyls [radulapins A-H (1-8)], four new prenylated bibenzyls (9-12), and seven known compounds (13-19). Compounds 1-11 were analyzed as racemates by chiral-phase separation. Their structures were determined by detailed analysis of their spectroscopic data and by single-crystal X-ray diffraction, chiral resolutions, and electronic circular dichroism measurements. Using an MTT assay, these dimers (1-8) showed significant cytotoxic activity against a panel of human Cancer cell lines. Further investigation revealed that compound 4 induces PC-3 cell death via mitochondrial-derived Apoptosis.