Diterpenoids from the leaves of Casearia kurzii showing cytotoxic activities.

• Six new diterpenoids were isolated from Casearia kurzii. • The structures were elucidated by NMR data and ECD calculations. • The cytotoxic effects and mechanism were investigated. • Compound 4 showed anti-tumor effects using in vivo zebrafish model. A phytochemical investigation to obtain bioactive substances as lead compounds or agents for cancer led to the obtainment of six new and two known clerodane diterpenoids from the leaves of Casearia kurzii. Their structures were elucidated using NMR techniques and electronic circular dichroism (ECD) calculations. The subsequent biological cytotoxicity evaluation of these isolates toward human lung cancer A549, human cervical cancer HeLa, human chronic myeloid leukemia K562, and human hepatocellular carcinoma HepG2 was carried out. The most active compound 4 with an IC 50 value of 9.7 μM against HepG2 cells was selected to examine the cytotoxic mechanism, which induced the apoptosis and arrested the HepG2 cell cycle at S stage. The in vivo zebrafish experiments revealed that compound 4 had the property of inhibiting tumor proliferation and migration. [ABSTRACT FROM AUTHOR]