New ent-Kaurane and cleistanthane diterpenoids with potential cytotoxicity from Phyllanthus acidus (L.) Skeels

Six diterpenoids including three ent-kauranes (1-2, 4) and three cleistanthanes (3, 5-6) were isolated from the roots and stems of Phyllanthus acidus (L.) Skeels. Of them, (16S)-ent-16,17,18-tri-hydroxy-19-nor-kaur-4-en-3-one (1), phyllanthone A (2), and 6-hydroxycleistanthol (3) are new compounds, while the ent-kaurane diterpenoids were reported from the titled plant for the first time. Their structures were elucidated on the basis of the extensive spectroscopic analyses. Compounds 2 and 4-6 displayed cytotoxic potential with IC₅₀ values ranging from 1.96 to 29.15 μM. They also showed moderate anti-inflammatory activities (IC₅₀ = 6.30-12.05 μM). Particularly, the new ent-kaurane 2 displayed cytotoxic potential against HL-60 (IC₅₀ = 2.00 μM) and MCF-7 (IC₅₀ = 3.55 μM) cells, and anti-inflammatory activity (IC₅₀ = 6.47 μM).