Norcrohalane A, an Unusual C15 nor‐Halimane‐Type Diterpenoid from Croton crassifolius

An unusual C15nor‐halimane‐type diterpenoid, norcrohalane A (1), a new nor‐lasserane‐type sesquiterpenoid, norcrolasane A (2), along with four known compounds (3–6) were isolated from the roots of Croton crassifolius. Compound 1 represents the first example of a C15nor‐halimane‐type diterpenoid, which features a rare 6/6/6 tricyclic ring system, and the A ring is aromatic. Compound 2 is a rare nor‐lasserane‐type sesquiterpenoid. Their structures and absolute configurations were established by a combination of MS, NMR, ECD calculation, and single‐crystal X‐ray diffraction analyses. The anti‐neuroinflammatory activities of 1–6 were evaluated for their inhibitory effects on nitric oxide (NO) production in LPS induced BV2 cells, and compounds 1 and 2 showed moderate inhibition on NO production with IC50 values of 26.82 ± 0.61 and 17.35 ± 0.78 μM, respectively.