Bioactive 5/5/5/6 Four–Ring System Iridoids from Plumeria alba L.

Abstract

Two rare 5/5/5/6 four‐ring system iridoids, allamancins A and B (1 and 2) together with one known biogenetically related iridoid derivative, 3‐O‐methyallamancin (3) were isolated from the flowers of Plumeria alba L. The structures of these iridoid derivatives were determined by comprehensive spectroscopic analyses. The absolute configuration of 1 was confirmed by X‐ray crystallographic analysis. The inhibitory activities of compounds 1‐3 against nitric oxide (NO) production induced and three cancer cell lines were evaluated in vitro. Compounds 1 and 3 showed inhibitory activities on NO production with IC50 values of 18.3 ± 0.12 and 22.1 ± 0.14 µM, respectively. Compounds 1‐3 showed moderate inhibitory activities against cancer cell lines of A549, Hela and MCF‐7.