Cytotoxic indole alkaloids from Nauclea orientalis

<p>A new indole alkaloid, nauclorienine (<b>1</b>), along with seven known alkaloids (<b>2–8</b>), were isolated from the stems and leaves of <i>Nauclea orientalis</i>. Among them, nauclorienine (<b>1</b>) was a new indole alkaloid holding a rare corynanthe-type skeleton, and the known compounds (<b>2–8</b>) were isolated from <i>N. orientalis</i> 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 <i>in vitro</i>. Alkaloids <b>1–4</b> exhibited significant inhibitory effects against various human cancer cell lines with IC<sub>50</sub> values comparable to those of cisplatin.</p>