Meroterpenoids with diverse structures and anti-inflammatory activities from Rhododendron anthopogonoides

Eight pairs of meroterpenoid enantiomers and four achiral meroterpenoids were isolated from Rhododendron anthopogonoides Maxim. Seventeen of them, named (+)-/(-)-anthoponoids A-G, (+)-daurichromene D, and anthoponoids H and I, are undescribed compounds with structural diversity. Their structures were characterized herein by a combined application of spectroscopic techniques, X-ray crystallographic analysis, ECD calculation, and the modified Mosher's method. (+)-/(-)-Anthoponoid A and anthoponoid I are the first Rhododendron meroterpenoids found to possess a hexahydroxanthene motif and a diterpene unit, respectively. Some isolates were identified as NF-κB pathway inhibitors, and (+)-anthoponoid E, (-)-anthoponoid G, and anthoponoid H showed suppressive effects on LPS-induced inflammatory responses in RAW 264.7 macrophages.