Hinokiflavone was isolated as the cytotoxic principle from the drupes of Rhus succedanea L. A comparison of the cytotoxicity of 1 and other related biflavonoids, including amentoflavone, robustaflavone, agathisflavone, rhusflavone, rhusflavanone and its hexaacetate, succedaneaflavanone and its hexaacetate, cupressuflavone, neorhusflavanone, volkensiflavone and its hexamethyl ether, spicataside and its nonaacetate, morelloflavone and its heptaacetate and heptamethyl ether. GB-1a and its hexamethyl ether and 7'-O-beta-glucoside , and GB-2a, indicates that an ether linkage between two units of apigenin as seen in 1 is structurally required for significant cytotoxicity. Compounds 13 and 20 also demonstrated significant cytotoxicity.
