Revision of the absolute configurations of Pallavicinia diterpenoids and further discovery of their Diels−Alder cycloadducts

Owing to their intricate molecular frameworks and copious chiral centers, the structural identification and configurational assignment of natural products are challenging tasks. Comprehensive spectral data analysis is crucial for the confirmation of absolute configurations. Ignoring critical parameters will lead to false structure, which may confuse the total synthesis and drug development. Herein, the configurations of seven heterogeneous Pallavicinia diterpenoids (PDs) isolated from Pallavicinia liverworts are revised using a combination of single-crystal X-ray diffraction and electronic circular dichroism (ECD) calculations. Meanwhile, identification of five unprecedented PD heterodimers PD-dimers A–E ( 18 – 22 ) along with eleven previously undescribed PDs ( 5 – 9, 13 – 17, 23 ) obtained by the reinvestigation of the Chinese liverwort Pallavicinia subciliata have resulted in corrections and support the revised conclusions. The absolute configurations of seven heterogeneous Pallavicinia diterpenoids were revised using a combination of single-crystal X-ray diffraction and ECD calculations. Meantime, five unprecedented heterodimers were obtained from P. subciliata .