Rearranged 19- nor-7,8- seco-labdane diterpenoids and Diels-Alder cycloadducts from the Chinese liverwort Pallavicinia ambigua: Structural elucidation, photoinduced rearrangement, and cytotoxic activity

Two distinctive rearranged 19-nor -7,8-seco-labdane diterpenoids ( 1 and 2 ) with a novel tetracyclo[5.2.1.02,5.04,10]decane skeleton, a derivative of the open tetrahydrofuran ring ( 7 ), three dimeric compounds (8-10), and four revised homologs (3-6) were obtained from Chinese liverwort Pallavicinia ambigua. Their structures were identified via combined analysis of their spectroscopic data, single-crystal X-ray diffraction patterns, and ECD calculations. The light-driven conversion of compound 5 to compounds 1-4 demonstrated that photochemically induced postmodification involved in biosynthesis is an important way to diversify natural structures. A preliminary cytotoxicity assay revealed that compound 5 showed significant inhibition in the human prostate cancer (PC-3) cell line via an apoptotic pathway.(c) 2023 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.