Structurally diverse diterpenoids from <i>Trigonostemon howii</i>

<p>Phytochemical investigation on the stems and leaves of <i>Trigonostemon howii</i> resulted in the isolation of a new abietane diterpenoid, trigohowimine A (<b>1</b>), along with seven known structurally diverse diterpenoids (<b>2</b>–<b>8</b>). The structure of <b>1</b> was elucidated by extensive spectroscopic methods and the known compounds were identified by comparison with data reported in the literature. New compound <b>1</b> was evaluated for its cytotoxicities against five human cancer cell lines: HL-60, SMMC-7721, A-549, MCF-7 and SW480. Compound <b>1</b> showed significant inhibitory effects against various human cancer cell lines with IC<sub>50</sub> values ranging from 0.82 to 8.53 μM.</p>