ent ‐Atisane Diterpenoids From Euphorbia micractina and Their Cytotoxic Activity

ABSTRACT 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 IC 50 value from 7.5 to 10.1 µM.