Carbazole alkaloids from Clausena hainanensis with their potential antiproliferative activities.

Five new carbazole alkaloids, clausehainanines A-E (1-5), together with seven known analogues (6-12) were isolated from the stems and leaves of C. hainanensis. Their structures were elucidated by extensive spectroscopic methods. Among them, compounds 1-5 were an unusual type of carbazole alkaloids, possessing diverse isopentenyl derivatives as substituents at C-2. All isolated compounds were evaluated for their antiproliferative activities against five human cancer cell lines: HL-60, SMMC-7721, A-549, MCF-7 and SW480 in vitro. Alkaloids 1-12 showed significant antiproliferative effects against various human cancer cell lines with IC50 values ranging from 0.12 to 15.56 μM. These findings suggest that the discoveries of these carbazole alkaloids with significant cytotoxic activities isolated from C. hainanensis could be of great importance to the development of new anticancer agents.