Rearranged Clerodane Diterpenoids from the Stems of Tinospora baenzigeri

Four new rearranged clerodane-type diterpenoids (1-4), a new glucoside (5), and six known compounds (6-11) were obtained from the EtOAc crude extract of Tinospora baenzigeri stem. The structures of the new compounds were elucidated by interpreting their spectroscopic data, particularly 1D and 2D NMR. Single-crystal X-ray diffraction analysis was subsequently performed to confirm the structures and relative configurations of compounds 1-4. These compounds are rare examples of rearranged clerodanes, particularly compound 4, possessing a fully oxidized tetrahydrofuranyl ring. The isolated compounds were assayed for their protective effect against N-acetyl- p-aminophenol (APAP)-induced HepG2 cell damage. Compounds 8, 9, and 11 showed hepatoprotective activity at 10 μM with 17.0, 19.2, and 39.0% inhibition, respectively, whereas rearranged clerodanes (1-3 and 5) were weakly active.