Anthraquinones from Neonauclea calycina and their inhibitory activity against DNA topoisomerase II.

In a series of searches for DNA topoisomerase II inhibitors from naturally occurring compounds, a wood extract of Neonauclea calycina MERR. (Rubiaceae) showed a moderate effect in vitro. Purification of the extract resulted in the isolation of seven known anthraquinones. The structures were characterized as damnacanthal, rubiadin 1-methyl ether, nordamnacanthal, morindone, damnacanthol, lucidin 3-O-primeveroside and morindone 6-O-primeveroside by spectral analysis, respectively. Damnacanthal and morindone showed an intensive inhibitory effect against topoisomerase II (IC50: 20 micrograms/ml and 21 micrograms/ml).