Minor lactones from a water decoction of the hook-bearing stem of Uncaria rhynchophylla

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