Structurally diverse diterpenoids from Trigonostemon howii

Phytochemical investigation on the stems and leaves of Trigonostemon howii resulted in the isolation of a new abietane diterpenoid, trigohowimine A (1), along with seven known structurally diverse diterpenoids (2–8). The structure of 1 was elucidated by extensive spectroscopic methods and the known compounds were identified by comparison with data reported in the literature. New compound 1 was evaluated for its cytotoxicities against five human cancer cell lines: HL-60, SMMC-7721, A-549, MCF-7 and SW480. Compound 1 showed significant inhibitory effects against various human cancer cell lines with IC₅₀ values ranging from 0.82 to 8.53 μM.