Crassins A–H, Diterpenoids from the Roots of <i>Croton crassifolius</i>

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).