Hinokiflavone, a cytotoxic principle from Rhus succedanea and the cytotoxicity of the related biflavonoids.

Hinokiflavone (1) 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 (2), robustaflavone (3), agathisflavone (4), rhusflavone (5), rhusflavanone (6) and its hexaacetate (7), succedaneaflavanone (8) and its hexaacetate (9), cupressuflavone (10), neorhusflavanone (11), volkensiflavone (12) and its hexamethyl ether (13), spicataside (14) and its nonaacetate (15), morelloflavone (16) and its heptaacetate (17) and heptamethyl ether (18), GB-1a (19) and its hexamethyl ether (20) and 7"-O-beta-glucoside (21), and GB-2a (22), 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.