Hunterlanines A–F, Neuroprotective Monoterpenoid Indole Alkaloid Heterodimers from <i>Hunteria zeylanica</i>

Six novel monoterpenoid indole alkaloid (MIA) heterodimers, hunterlanines A-F (<b>1</b>-<b>6</b>), were isolated from <i>Hunteria zeylanica</i>. Compounds <b>1</b> and <b>2</b> possess unprecedented carbon skeletons featuring cage-like 6/5/6/6/6/5/6 heptacyclic and 6/5/6/6/6/6 hexacyclic cores, respectively. Compounds <b>3</b> and <b>4</b> represent the first MIA-phenylpropanoid heterodimers characterized by an unusual C-C and N-C connectivity, forming two different 6/5/5/8/6 pentacyclic scaffolds. Compounds <b>5</b> and <b>6</b> exemplify novel heterodimers in which the MIA moiety was coupled with indole derivative or indole via C-C linkages. Their structures were established by spectroscopic analyses, X-ray crystallography, and quantum chemical calculations. Notably, compounds <b>1</b>, <b>4</b>, and <b>6</b> exhibited significant neuroprotective activity against l-glutamate-induced neural injury in HT-22 cells.