New alkaloids from Melodinus fusiformis and their cytotoxic activities

Four new alkaloids, meloformisine A (1), meloformine B (2), meloformine F (3), meloformine G (4), along with five known alkaloids (5-9) were isolated from the leaves and twigs of Melodinus fusiformis. Their structures were elucidated on the basis of detailed spectroscopic evidence, including 1D and 2D NMR, MS, and single-crystal X-ray diffraction analysis. The structure of 1 was a novel indole alkaloid with an unprecedented 6/5/5/5/5 pentacyclic skeleton. The evaluation of inhibition activity against human A-549, MCF-7, and K-562 cell lines showed that compounds 1, 2, 6 and 8 exhibited different levels of cytotoxic activities, with IC₅₀ values ranging from 8.72 to 47.32 μM, respectively.