| Sumario: | Five previously undescribed diterpenoids (1–5) along with four known ones (6–9) were isolated from the roots of Croton crocodilorum. Most notably, the four ent -3,4- seco -atisane diterpenoids (2–5) biosynthesized from the ent -atisane diterpenoid (1) were crotogoudin derivatives. Their structures were elucidated by spectroscopic data including HRESIMS and extensive 1D and 2D NMR investigations. The absolute configuration of compounds (−)-1, (−)-3 and (−)-6 was determined by vibrational circular dichroism (VCD) and Raman optical activity (ROA) spectroscopies along with density functional theory calculations. Their plausible biosynthetic pathway was proposed. All isolated diterpenoids were evaluated for their antiproliferative activity against sensitive and resistant human colorectal cancer cells (HCT116 and HT-29). Compounds 3, 5, 6 and 7 displayed more potent activities than the two positive controls (5 FU and irinotecan) against the two cancer cell lines. [Display omitted] • Five previously undescribed diterpenoids were isolated from Croton crocodilorum roots. • Their structures were established by spectroscopic methods (HRMS, NMR, VCD and ROA). • Compounds 3 , 5–7 exhibited significant antiproliferative activities against HCT 116 and HT-29 cell lines. • Structure activity relationship showed the interest of an a,b -unsaturated ketone function.
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