A new flavonol from the kino of Eucalyptus citriodora

A new flavonol, 6-[1-(p-hydroxyphenyl)ethyl]rhamnocitrin (3) together with two known compounds, kaempferol (4) and 7-O-methyl aromadendrin (5) were isolated from the kino of Eucalyptus citriodora and their structures were elucidated on the basis of spectroscopic methods including 2D NMR spectra. Rhamnocitrin (1), 6-[1-(p-hydroxyphenyl)ethyl]-7-O-methyl aromadendrin (2), previously isolated from this plant and compounds 3-5 were tested for inhibitory activity against 15-lipoxygenase. All compounds exhibited moderate to strong inhibitory activities, of which compounds 2, 3 and 5 showed stronger inhibitory activity (IC₅₀ 19.7 ± 0.5, 29.3 ± 0.9 and 31.4 ± 1.0 μM, respectively) than the positive control quercetin (IC₅₀ 37.5 ± 0.8 μM).