Hepatoprotective Ring B-Seco Flavonoids and Sesquiterpenoids from the Bark of Cinnamomum cassia Presl

Two new ring B-seco flavonoids (1 and 2), five new cadinane sesquiterpenoids (3–7), and three previously described relevant isolates (8–10) are isolated from a beloved food and spice with medicinal properties (Cinnamomum cassia Presl’s bark). Structures of all isolates are determined using the spectroscopic technique, X-ray crystallography method, and quantum chemical calculation. Notably, compounds 1 and 2 are rare ring B-seco flavonoids with a 6/6/5/5 tetracyclic skeleton. Ring B-seco flavonoids are unusual secondary metabolites, and only seven ring B-seco flavonoids featuring the 6/6/5/5 tetracyclic skeleton have been reported. The biogenetic pathways for compounds 1 and 2 are proposed. Alcohol-induced hepatocyte injury model is employed to evaluate their hepatoprotective activities. The results display that all compounds exhibit different extents of hepatoprotective activities, integrating into cell viability amelioration and fat accumulation alleviation. The potencies of compounds 5 and 10 are better than those of silymarin. Hepatoprotective activities of oppositane sesquiterpenoids are first reported.