Calycopterones and calyflorenones, novel biflavonoids from Calycopteris floribunda

Neocalycopterone (1) and its methyl ether (2), along with two new biflavonoids, calyflorenones A (3) and B (4), were isolated from dried leaves of Calycopteris floribunda (Combretaceae). Structures 1-4 were investigated by spectroscopic methods. The relative stereochemistry of 3 and 4 was deduced through NOE and ROESY experiments, comparative CD and optical rotation evaluations. Cytotoxicity test results of 1 and 2 are reported. The monoflavonoid penduletin was isolated as a minor component from C. floribunda for the first time.