Phyllanflexoid C: first example of phenylacetylene-bearing 18-nor-diterpenoid glycoside from the roots of Phyllanthus flexuosus

Three structurally interesting new diterpenoids, phyllanflexoids A-C (1-3), together with cleistanthol (4) were isolated from the roots of Phyllanthus flexuosus. Their structures with the absolute stereochemistry were elucidated on the basis of comprehensive spectroscopic analysis, computational method, and acidic hydrolysis in the case of 3. Compounds 1-3 were phenylacetylene-bearing tricyclic diterpenes and 3 was the first example of phenylacetylene-bearing 18-nor-diterpenoid glycoside. Compounds 1, 2, and 4 exhibited weak cytotoxicity against human esophagus cancer cell ECA109 with IC50 of 42.7, 21.4, and 24.5 μM, respectively.