Two new lignans, phillyroside A(1) and phillyroside B(2), together with three new phenylethanoid glycoside, forsythoside K(3), forsythoside L(5) and forsythol L (4), while compounds 4 was an aglycon of forsythoside L(5), were isolated from the aerial parts of Forsythia suspensa (Thunb.) Vahl. Their structures were elucidated by comprehensive analyses of standard spectroscopic data (MS, IR, and NMR) and the in vitro antioxidant activity of five new compounds were evaluated in DPPH and ABTS radical scavenging experiment and ferric reducing ability of plasma (FRAP) experiment. Compounds 4 and 5 exhibited antioxidant activity with IC50 values ranging from 112.49 to 153.58 μM in DPPH experiment and 45.43 to 64.09 μM in ABTS experiment.
Keywords: Forsythia suspensa; antioxidant activity; phenylethanoid glycoside; phenylpropanoid glycoside.