Crassins A–H, Diterpenoids from the Roots of Croton crassifolius

Phytochemical investigation of the 70% acetone extract of Croton crassifolius roots afforded eight new diterpenoids, crassins A–H (1–8), and 19 known compounds. The structures of the new compounds were determined by spectroscopic methods, and their absolute configurations were determined by electronic circular dichroism, single-crystal X-ray diffraction analysis, comparison with literature data, and biogenetic considerations. Crassins A (1) and B (2) are new ring B-rearranged diterpenoids, whereas crassin C (3) is a new ring A-rearranged diterpenoid. Crassin H (8) exhibited selective cytotoxicity against A549 cells (IC50 5.2 μM) compared with HL-60 cells (IC50 11.8 μM). The known compound chettaphanin-II exhibited moderate activity against the A549 and HL-60 cell lines (IC50 8.4 and 10.5 μM, respectively).