Minor indoloquinolizidine monoterpene alkaloids from an aqueous extract of the hook-bearing stem of <i>Uncaria rhynchophylla</i>

Six minor undescribed indoloquinolizidine monoterpene alkaloids, uncarrhynchophyllines F - K (<b>1 </b>-<b> 6</b>), were isolated from an aqueous decoction of the hook-bearing stems of <i>Uncaria rhynchophylla</i> (gou-teng). Their structures were determined by spectroscopic data analysis in combination with electron circular dichroism (ECD) and NMR calculations. Compounds <b>1 </b>-<b> 4</b> are rare indoloquinolizidine iminium zwitterions, while <b>5</b> exhibited protective effects against APAP induced liver cell injury.