Monoterpenoid indole alkaloid dimers from Melodinus tenuicaudatus and their cytotoxicity

Phytochemical investigation of the stems and leaves of the plant Melodinus tenuicaudatus led to the isolation of four previously unreported monoterpene indole alkaloid dimers, namely melocaudusines A-D (1-4), together with four known analogues (5-8). Comprehensive analysis of the spectroscopic data, combined with computational methods, enabled the structural elucidation and assignment of the absolute configurations of these alkaloids. All isolated compounds exhibited good cytotoxicity against one to three tumor cell lines. Among them, compounds 1 and 4 showed potency comparable to that of the positive control, with IC₅₀ values ranging from 3.72 to 12.92 μM.