Isolation and bioactivity evaluation of ten novel norlignans and additional neuroprotective compounds from Curculigo...

Ten new norlignans (1-10) and nineteen known compounds (11-29) were isolated from Curculigo gracilis. The structures of the new norlignans were elucidated by comprehensive spectroscopic analysis, incorporating one-dimensional and two-dimensional nuclear magnetic resonance spectroscopy (1D/2D NMR), high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), and electronic circular dichroism (ECD) measurements. The neuroprotective effects of compounds 1-29 were evaluated in an in vitro model of glutamate-induced oxidative stress using SH-SY5Y cells. The results revealed that all compounds exhibited certain protective effects with cell viability values ranging from 54.6 % to 89.1 %, significantly higher than that of the glutamate-induced group (cell viability: 45.3 %). Notably, compound 17 displayed the strongest activity, with a cell survival rate of 89.1 % at a concentration of 25 μM. The benzannulated seven-membered ring norlignans (compounds 1-3 and 12-16) demonstrated particularly strong neuroprotective efficacy and their preliminary structure-activity relationships (SARs) were discussed. In addition, Western blot analysis indicated that compound 14 exerted a protective effect by regulating the expression of Nrf2/HO-1.