Antiproliferative activity of semisynthetic xylopic acid derivatives.

Two ent-kaurene diterpenoids, ent-15-β-acetyloxy-kaur-16-en-19-oic acid (xylopic acid) 1 and ent-7-oxo-kaur-16-en-19-oic acid 2 were isolated from the fruits of Xylopia aethiopica. Chemical manipulation of xylopic acid yielded ent-kaurane derivatives 3, 4, 5, and 6. Their structures were elucidated by spectroscopic analysis, including 1 D- and 2 D-NMR spectroscopies. The antiproliferative activities of compounds 1, 2, 3, 4, and 6 were tested on breast MCF7 and SkBr3, endometrial Ishikawa, ovarian BG-1, mesothelioma IST-MES1 and hepatocellular HepG2 human tumor cells, and on mammalian MRC-10 fibroblast cells. Ketone 2 showed significant antiproliferative activity against MFC7 human breast cancer cells (IC50 = 3 ± 1 µM) and A549 pulmonary adenocarcinoma (8 ± 1 µM), that was higher than the well-known anti-cancer agent cisplatin (IC50 = 19 ± 3 and 15 ± 4 µM, respectively).