Aspidosperma-type bisindole alkaloids from Melodinus suaveolens and their antiproliferative activities

Melosuadimins A-L (1-12), twelve undescribed monoterpenoid dimeric alkaloids with different subsets of aspidosperma-type alkaloid units were isolated from Melodinus suaveolens. Their structures were elucidated through extensive spectroscopic data analysis. Notably, melosuadimin A (1) was a vindoline-aspidosperma type bisindole alkaloid with a dihydrofuran ring linkage. Melosuadimins B (2) and C (3) were proposed as oxidation and ring-opening derivatives of melosuadimin A. Additionally, melosuadimin D (4), featuring a unique 1,2-oxazinane ring, was possibly produced through rearrangement from melosuadimin B. The in vitro cytotoxic potential of these compounds against three colorectal cancer cell lines was evaluated, revealing that 2 exhibited marked antiproliferative activity, inducing apoptosis and G2/M cell cycle arrest.