Diterpenoids from Sigesbeckia glabrescens with anti-inflammatory and AChE inhibitory activities

Fourteen previously undescribed diterpenoids, including seven ent-pimarane-type diterpenoids and seven phytane-type diterpenes, together with five known ones, were isolated from the aerial parts of Sigesbeckia glabrescens. The structures and absolute configurations of undescribed compounds were elucidated based on extensive spectroscopic techniques, ECD calculations, Mo₂(OAC)₄-induced ECD, Rh₂(OCOCF₃)₄-induced ECD, calculated ¹³C NMR, and chemical methods. In the anti-inflammatory bioassay, siegetalis H showed potent inhibitory effect on LPS-induced NO production in RAW264.7 murine macrophages with an IC₅₀ value at 17.29 μM. Furthermore, siegetalis H suppressed the protein expression of iNOS and COX-2 in LPS-stimulated RAW264.7 cells. Mechanistically, siegetalis H suppressed the phosphorylation and degradation of IκBα, as well as the activation of the NF-κB signaling pathway. In addition, the AChE inhibition assay displayed that 3-O-acetyldarutigenol had a remarkable inhibitory effect against AChE with an IC₅₀ value at 7.02 μM. Kinetic study on 3-O-acetyldarutigenol indicated that it acted as a mixed-type inhibitor, and the binding mode was explored by molecular docking.