Identification of a new naphthalene and its derivatives from the bulb of Eleutherine americana with inhibitory activity on lipopolysaccharide-induced nitric oxide production

A new naphthoquinone, (-)-3-[2-(acetyloxy)propyl]-2-hydroxy-8-methoxy-1,4- naphthoquinone (1) was isolated from the bulb of Eleutherine americana Merr. et Heyne (Iridaceae) together with two known compounds, eleutherinol (6) and 1,5-dihydroxy-3-methylanthraquinone (7) which were found in this species for the first time. The other known compounds, (-)-isoeleutherin (2), (+)-eleutherin (3), (-)-hongconin (4), and (+)-dihydroeleutherinol (5) which were reported previously from this species, were also isolated in the present study. Compounds 2-6 exhibited potent inhibitory activity on nitric oxide production in RAW 264.7 lipopolysaccharide-activated mouse macrophage cells with IC₅₀ values of 7.7, 11.4, 19.8, 21.7, and 34.4 μm, respectively, whereas the other two compounds, 1 and 7, were inactive. The structure of compound 1 was elucidated by spectroscopic data analysis including 1D and 2D NMR experiments.