RESUMO
Two rare 5/5/5/6 four-ring system iridoids, allamancinsâ 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 compoundsâ 1-3 against nitric oxide (NO) production induced and three cancer cell lines were evaluated inâ vitro. Compoundsâ 1 and 3 showed inhibitory activities on NO production with IC50 values of 18.3±0.12 and 22.1±0.14â µM, respectively. Compoundsâ 1-3 showed moderate inhibitory activities against cancer cell lines of A549, Hela and MCF-7.