ent-Atisane Diterpenoids From Euphorbia micractina and Their Cytotoxic Activity

Three new ent-atisane diterpenoids (1-3) and five known ones (4-8) were obtained from the bioactive fraction of E. micractina. Their structures and absolute configurations were elucidated by a comprehensive analysis of the spectroscopic data, including high-resolution electrospray ionization mass spectrometry, infrared, nuclear magnetic resonance, X-ray crystallography, and electronic circular dichroism data. Among them, compound 1 was the first example of an ent-atisane diterpenoid with an α-oriented hydroxyl group at C-7. In addition, the cytotoxicity of all the isolated ent-atisane diterpenoids was evaluated against human cervical carcinoma, human acute promyelocytic leukemia, and human hepatoma cell lines. Compound 3 demonstrated significant cytotoxic activity against the selected cell lines with an IC₅₀ value from 7.5 to 10.1 µM.