The unprecedented iridal lactone and adducts of spiroiridal and isoflavonoid from Belamcanda chinensis

Five novel iridal-type triterpenoid derivatives, including three unprecedented adducts of spiroiridal and isoflavonoid, named belamcandanins A–C (1–3), one unprecedented iridal lactone, named belamcanolide A (4), and one new and rare iridal epoxide, named belamcanoxide A (5), have been isolated from the rhizomes of Belamcanda chinensis, along with five known compounds. Their structures were elucidated on the basis of extensive spectroscopic analysis. Compounds 1–3 represent the first meroterpenoids composed of an isoflavonoid linked to a spiroiridal-triterpenoid. To the best of our knowledge, compound 4 is the first example of 5/6-fused bicyclic iridal lactone. Compounds 1–8 were evaluated for their in vitro cytotoxicity against five tumor cell lines. Among them, compounds 5–8 showed moderate cytotoxic activities against five cancer cell lines with IC50 values from 3.26 to 8.63 mM.