Hunterlanines A–F, Neuroprotective Monoterpenoid Indole Alkaloid Heterodimers from Hunteria zeylanica

Six novel monoterpenoid indole alkaloid (MIA) heterodimers, hunterlanines A-F (1-6), were isolated from Hunteria zeylanica. Compounds 1 and 2 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 3 and 4 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 5 and 6 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 1, 4, and 6 exhibited significant neuroprotective activity against l-glutamate-induced neural injury in HT-22 cells.