Cytotoxic indole alkaloids from Nauclea orientalis
A new indole alkaloid, nauclorienine (1), along with seven known alkaloids (2–8), were isolated from the stems and leaves of Nauclea orientalis. Among them, nauclorienine (1) was a new indole alkaloid holding a rare corynanthe-type skeleton, and the known compounds (2–8) were isolated from N. orientalis for the first time. Their structures were elucidated on the basis of extensive spectroscopic data analyses. All isolated compounds were evaluated for their cytotoxicities against five human cancer cell lines: HL-60, SMMC-7721, A-549, MCF-7 and SW480 in vitro. Alkaloids 1–4 exhibited significant inhibitory effects against various human cancer cell lines with IC50 values comparable to those of cisplatin.