Six unprecedented 2-(2-phenethyl)chromone dimers from agarwood of Aquilaria filaria

Six new dimeric 2-(2-phenylethyl)chromones ( 1 – 6 ) were successfully isolated from the ethanol extract of agarwood of Aquilaria filaria from Philippines under HPLC-MS guidance. Compounds 1 – 6 are all dimers formed by linking 5,6,7,8-tetrahydro-2-(2-phenylethyl)chromone and flindersia 2-(2-phenylethyl)chromone via a single ether bond, and the linkage site (C5-O-C8′′) of compound 2 is extremely rare. A variety of spectroscopic methods were used to ascertain their structures, including extensive 1D and 2D NMR spectroscopic analysis, HRESIMS, and comparison with literature. The in vitro tyrosinase inhibitory and anti-inflammatory activities of each isolate were assessed. Among these compounds, compound 2 had a tyrosinase inhibition effect with an IC 50 value of 27.71 ± 2.60 μM, and compound 4 exhibited moderate inhibition of nitric oxide production in lipopolysaccharide-stimulated RAW264.7 cells with an IC 50 value of 35.40 ± 1.04 μM.