Melokhanines A–J, Bioactive Monoterpenoid Indole Alkaloids with Diverse Skeletons from Melodinus khasianus

The new melokhanines A–J (1–10) and 22 known (11–32) alkaloids were isolated from the twigs and leaves of Melodinus khasianus. The new compounds and their absolute configurations were elucidated by extensive analysis of spectroscopic, X-ray diffraction, and computational data. Melokhanine A (1), composed of a hydroxyindolinone linked to an octahydrofuro­[2,3-b]­pyridine moiety, is an unprecedented monoterpenoid indole alkaloid. Melokhanines B–H (2–8) possess a new 6/5/5/6/6 pentacyclic indole alkaloid skeleton. Alkaloids 1–16, 25–27, 31, and 32 showed the best antibacterial activity against Pseudomonas aeruginosa (MIC range 2–22 μM). Among the seven dermatophytes tested, compound 1 showed significant inhibitory activity against Microsporum canis, M. ferrugineum, and Trichophyton ajelloi (MIC range 38–150 μM), i.e., half the efficacy of the positive control, griseofulvin.