19- nor -, 20- nor -, and tetranor -Halimane-Type Furanoditerpenoids from Croton crassifolius .

The phytochemical investigation of the roots of Croton crassifolius led to the isolation of 16 new halimane furanoditerpenoids, crohalifuranes A-P ( 1 - 16 ), along with 15 known analogues, 17 - 31 . The new structures including their absolute configurations were elucidated by NMR and MS data analysis, comparison of experimental and calculated electronic circular dichroism data, single-crystal X-ray diffraction data, and chemical methods. Crohalifuranes A ( 1 ) and B ( 2 ) are tetranor - and 19- nor -halimane diterpenoids featuring a rare decahydroacenaphthene core, respectively, which might be derived from the accompanying crassifoliusin A by loss of the furan ring or the C-19 substituent. Crohalifurane C ( 3 ) represents the first example of a 20- nor -halimane diterpenoid, and crohalifurane D ( 4 ) is characterized by an unusual 6,20-δ-lactone moiety. All compounds were examined for their inhibitory effects on nitric oxide (NO) production induced by lipopolysaccharide in RAW264.7 cells, and 2 and 23 exhibited moderate inhibition on NO production with IC ₅₀ values of 17.2 ± 1.3 and 23.7 ± 1.4 μM, respectively.