Two highly oxygenated nor-clerodane diterpenoids from Croton caudatus

Two highly oxygenated nor-clerodane diterpenoids, crocleropenes A and B (1 and 2), together with four known compounds (3–6) were isolated from the leaves and twigs of Croton caudatus. Their structures were elucidated by combination of extensive spectroscopic analysis and electronic circular dichroism (ECD) calculations. 1 and 2 represent the first examples of nor-clerodane-3,5(10)-diene diterpenoids. Compounds 1 and 2 exhibited weak cytotoxicity in vitro against MCF-7 cancer cells with IC50 values of 35.8 and 40.2 μM, respectively.