A new antioxidant flavonoid from the lianas of Gnetum macrostachyum.

A new flavonoid, named 5,7,2'-trihydroxy-5'-methoxyflavone (1), was isolated from the acetone extract of the lianas of Gnetum macrostachyum together with 5,7,4'-trihydroxy-3'-methoxyflavanone (2) and seven known stilbenoids (3-7). The structure of the new compound was determined by interpretation of its spectral data and chemical transformation. The isolated compounds showed radical scavenging activity against DPPH with IC(50) values in the range of 0.21-19.90 mM.