A new degradation method was developed for converting polymeric proanthocyanidins into highly bioactive flavan-3-ol derivatives in the presence of glutathione (GSH) as a nucleophile. Combining single-factor experiments and Box–Behnken factorial design (BBD), optimized degradation conditions were established. Grape seed proanthocyanidins were reacted with GSH at a ratio of 1 : 3 with 0.2 M methanolic HCl, a temperature of 55 °C and a reaction time of 30 min. The degradation products were largely isolated and prepared by one-step high-speed counter-current chromatography (HSCCC) and preparative HPLC. Three monomeric proanthocyanidins and four novel GSH conjugates were obtained with a high yield (85%) and high purity (over 91%). Also, the protective effects of all these compounds against H2O2-induced oxidative stress in PC-12 neuroblastoma cells were investigated. GSH conjugates were shown to be better at increasing the antioxidative effect than their underivatized monomers and GSH, indicating their better neuroprotective effects against oxidative stress.
