Isoxerophilins A and B, two diterpene heterodimers from Isodon xerophilus : structural elucidation and semisynthesis of isoxerophilin analogues

Two types of novel diterpene heterodimers, isoxerophilins A (1, ent -kaurane–sempervirane) and B (2, ent -kaurane–abietane), were isolated from the roots of Isodon xerophilus . Their structures and absolute configurations were determined by spectroscopic data and single crystal X-ray diffraction analysis. A bioinspired semisynthesis of ten isoxerophilin analogues, featuring a tandem oxidative dearomatization/intermolecular Diels–Alder reaction, has been achieved, and the transformation of ferruginol into a sempervirane scaffold was accomplished by the SIBX-mediated tandem reaction. Compound 12 promotes MICA/B expression on SMMC-7721 cells.