Two New Halimanes with a γ-Lactone from Croton argyratus.

The phytochemical investigation of the rainforest plant Croton argyratus (Euphorbiaceae) led to the isolation of two halimane-type diterpenes, crotargyolides A (1) and B (2), with an uncommon γ-lactone ring at C-5 and C-9, together with a crotofolane-type diterpene, 3-hydroxylated crotofolin C (3, crokocrotogenoid A), and the known clerodane diterpenes, junceic acid (4) and epoxyjunceic acid (5). The structures of the newly isolated compounds were elucidated by various NMR techniques, high resolution (HR)MS analysis, and electronic circular dichroism (ECD) spectroscopy. The proposed biosynthetic pathway of 1 from 4 was discussed. Crotargyolide A (1) and known compounds 4 and 5 were evaluated for antiproliferative activity and displayed no growth inhibitory effect toward all tested tumor cell lines.