Minor lactones from a water decoction of the hook-bearing stem of <i>Uncaria rhynchophylla</i>

Six undescribed minor lactones (uncarterolides A–F, <b>1</b>–<b>6</b>) were isolated from a water decoction of the hook-bearing stems of <i>Uncaria rhynchophylla</i> (gou-teng). Their structures were determined by spectroscopic data analysis, along with electronic circular dichroism (ECD) and NMR calculations. Compounds <b>3–6</b> are abnormal homo-monoterpene enolic ether lactones sharing structural features with monoterpene alkaloids from gou-teng, as well as compounds <b>3</b> and <b>6</b> attenuated APAP-induced HepG2 cell damage by increasing the cell viability from 59.39% to 75.87% and 74.43%, respectively.