Stephacidin A and B: Two Structurally Novel, Selective Inhibitors of the Testosterone-Dependent Prostate LNCaP Cells

Two novel antitumor alkaloids, Stephacidin A and B, were isolated from the solid fermentation of Aspergillus ochraceus WC76466. Both alkaloids exhibit in vitro cytotoxicity against a number of human tumor cell lines; however, stephacidin B demonstrated more potent and selective antitumor activities, especially against prostate testeosterone-dependent LNCaP cells with IC50 value of 60 nM. The structures of stephacidin A and B were established on the basis of the NMR data and X-ray crystallography. With 15 rings and 9 chiral centers, stephacidin B represents one of the most structurally complex and novel alkaloids occurring in nature.