Melokhanines A–J, Bioactive Monoterpenoid Indole Alkaloids with Diverse Skeletons from <i>Melodinus khasianus</i>

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