Plumeriapropionics A–E, Carboxyl-Substituted Phenylpropionic Acid Derivatives with Anti-Inflammatory Activity from Plumeria rubra L.

Five rare carboxyl-substituted phenylpropionic acid derivatives, plumeriapropionics A–E (1–5), together with one known analog, cerberic acid B (6), were isolated from flowers of Plumeria rubra L. Their structures were elucidated using comprehensive spectroscopic methods. To date, only one compound of this structural type has been reported. The inhibitory activities of compounds 1–6 against nitric oxide (NO) production induced by lipopolysaccharide (LPS) were evaluated in vitro using mouse macrophage RAW264.7 cells. Compounds 1–6 showed remarkable inhibitory activities on NO production, with IC50 values in the range of 6.52 ± 0.23 to 35.68 ± 0.17 µM. These results indicate that the discovery of carboxyl-substituted phenylpropionic acid derivatives from the flowers of P. rubra, which show significant anti-inflammatory properties, could be of great importance for the research and development of novel natural anti-inflammatory agents.