Pyranochromones with Anti-Inflammatory Activities in Arthritis from Calophyllum membranaceum

Eleven new pyranochromones, calomembranone A–K (1–11), two new pyranocoumarins, calopolyanolide E and F (12 and 13), together with six known analogues (14–19) were isolated from the leaves of Calophyllum membranaceum. Their structures and absolute configurations were elucidated by analysis of spectroscopic data, computational calculations, as well as X-ray crystallography of 4 and 9. The anti-inflammatory activities of all the isolates were evaluated by measuring their NO inhibitory effects in LPS-stimulated RAW 264.7 cells. Structure–activity relationships are also discussed. Compound 7 showed the strongest NO inhibition (IC50 = 0.92 μM). Oral administration of 7 dose-dependently reduced the paw swelling and downregulated neutrophil-to-lymphocyte ratio in the carrageenan-induced acute arthritis mice model. Molecular dynamics simulation and cellular thermal shift assay results indicated that 7 participated in a robust and stable interaction with the active site of TLR4. Compound 7 also suppressed the inflammation in arthritis through the regulation of TLR4 mediated signal transduction via IKK/NF-κB signaling pathway and the consequent reduction of IL-2, IL-4, and IL-5.