Coumarins from Tridax procumbens L. and their anti-inflammatory activity

Twenty-two coumarins, including seven previously undescribed compounds, which comprised a pair of enantiomers (2a/2b) and five other compounds (1, 3-6), were isolated from the whole plant of Tridax procumbens L. Their structures were identified using spectroscopic techniques (NMR, IR, MS, and optical rotation), NMR calculation with DP4+ probability analysis, and ECD calculations. The anti-inflammatory effect of coumarins was evaluated by their inhibition of lipopolysaccharide-stimulated nitric oxide production in RAW 264.7 macrophages. (2'S,3'S)-3'-methyl-4'-hydroxylobliquin (6), 6-hydroxy-7-(3,3-dimethylallyloxy) coumarin (18), puberulin (20), and altissimacoumarin N (21) demonstrated inhibitory effects with respective IC₅₀ values of 24.55, 31.72, 31.30, and 32.14 μM. Mechanistic studies further demonstrated that compound 6 concentration-dependently suppressed the production of pro-inflammatory mediators (iNOS, COX-2, IL-1β, and IL-6) by blocking NF-κB nuclear translocation. The study lays the foundation for developing coumarins from T. procumbens as lead compounds for anti-inflammation.