Optically active bisbibenzyls from Bazzania trilobata: isolation and stereochemical analysis by chromatographic, chiroptical, and computational methods

Bazzanin S, a new chlorinated bisbibenzyl of the isoplagiochin D type, as well as isoplagiochin D itself were isolated from the liverwort Bazzania trilobata. The structure of bazzanin S was elucidated based on extensive NMR spectral evidence and by mass spectrometry. Both macrocyclic compounds, bazzanin S and isoplagiochin D, as well as previously reported bazzanins exhibit optical activity, but are not enantiopure in nature. The enantiomeric ratios of a broad array of different cyclic bisbibenzyls, isoplagiochin D, bazzanins A–C and F–J, and bazzanin S, were determined by HPLC on a chiral phase. Exemplarily for the halogen-free parent compound isoplagiochin D, elucidation of the absolute configuration was achieved by quantum chemical CD calculations.