Anti-inflammatory sesquiterpenoids from Chloranthus japonicus

Ten undescribed sesquiterpenoids were isolated from Chloranthus japonicus Sieb., including (4R,5S,6R,8R,10R)-4-hydroxy-6-O-β-d-glucosyleudesman-7(11)-en-8,12-olide (1), (1R,4R,5R,8S,10R)-1,4-dihydroxy-15-(2-methylbutyryloxy)eudesman-7(11)-en-8,12-olide (2),(1R,4S,5R,8S,10R)-1,4-dihydroxy-15-(2-methylbutyryloxy)eudesman-7(11)-en-8,12-olide (3), (1R,3S,4R,5S,8S,9S,10S)-8,9-epoxy-15-hydroxylindenran-7(11)-en-8,12-olide (4), (1R,3S,4R,5S,8S,9S,10S)-8,9,15-trihydroxylindenran-7(11)-en-8,12-olide (5), (1R,3S,4R,5S,6R,8S,10S)-6-acetoxyl-4-hydroxy-15-O-β-d-glucosyllindenran-7(11)-en-8,12-olide (6), (1R,3S,4R,5S,6R,8S,10S)-15-hydroxy-4-O-β-d-glucosyllindenran-7(11),8(9)-dien-8,12-olide (7), japonilides A-C (8-10), along with 19 known compounds. Compounds 8-10 are rare 5,6-seco-germacrane-type sesquiterpenoids, and only one of this type sesquiterpenoid has been reported to be isolated from C. anhuiensis. 9-Ketocurzerene (27) was first reported from a natural source. The structures and absolute configurations of the compounds were elucidated through a combination of spectroscopic data interpretation, quantum-chemical calculation, DP4+ probability analysis, and single-crystal X-ray diffraction analysis. Compounds 8, 12, 16 and 22 exhibited significant inhibitory effects on NO production in lipopolysaccharide-stimulated RAW 264.7 macrophages, with IC₅₀ values of 22.99 ± 2.71, 24.34 ± 1.36, 23.69 ± 2.83, and 21.23 ± 1.34 μmol/L, respectively. Western blotting studies demonstrated that compound 8 inhibited the expression of nitric oxide synthase and cyclooxygenase-2, which act as key mediators in the inflammatory response.