Highly oxygenated clerodane furanoditerpenoids from the leaves and twigs of Croton yunnanensis

The phytochemical investigation of the leaves and twigs of Croton yunnanensis resulted in the isolation of eight new clerodane furanoditerpenoids, named croyunfuranoids A−H (1−8), along with three known analogs (9−11). The structures of these compounds were elucidated using spectroscopic analyses, and their absolute configurations were determined through a combination of electronic circular dichroism (ECD) calculations and single-crystal X-ray diffraction. Notably, Croyunfuranoid D (4) is identified as a rare 18,19-dinor-clerodane diterpenoid. Additionally, the structure of a previously reported diterpenoid, crotonyunnan B, was revised. All isolated compounds were evaluated for their inhibitory activities on nitric oxide (NO) production in LPS-induced RAW 264.7 macrophages. Among them, compounds 5 and 6 demonstrated significant inhibitory effects, with IC₅₀ values of 20.33 ± 2.31 and 22.80 ± 1.31 μmol·L⁻¹, respectively.