Potential antioxidative components from Syringa oblata Lindl stems revealed by affinity ultrafiltration with multiple drug targets

Traditional Chinese medicine is the main source of natural products due to its remarkable clinical efficacy. Syringa oblata Lindl (S. oblata) was widely used because of its extensive biological activities. However, to explore the antioxidant components of S. oblata against tyrosinase, the experiments of antioxidation in vitro were employed. At the same time, the determination of TPC was also use to assess the antioxidant ability of CE, MC, EA and WA fractions and the liver protective activity of the EA fraction was evaluated by mice in vivo. Next, UF-LC-MS technology was performed to screen and identify the efficient tyrosinase inhibitors in S. oblata. The results showed that alashinol (G), dihydrocubebin, syripinin E and secoisolariciresinol were characterized as potential tyrosinase ligands and their RBA values were 2.35, 1.97, 1.91 and 1.61, respectively. Moreover, these four ligands can effectively dock with tyrosinase molecules, with binding energies (BEs) ranging from 0.74 to -0.73 kcal/mol. In addition, tyrosinase inhibition experiment was employed to evaluate the tyrosinase inhibition activities of four potential ligands, the result showed that compound 12 (alashinol G, IC50 = 0.91 ± 0.20 mM) showed the strongest activity to tyrosinase, followed by secoisolariciresinol (IC50 = 0.99 ± 0.07 mM), dihydrocubebin (IC50 = 1.04 ± 0.30 mM) and syripinin E (IC50 = 1.28 ± 0.23 mM), respectively. The results demonstrate that S. oblata might have excellent antioxidant activity, and UF-LC-MS technique is a effective means to filter out tyrosinase inhibitors from natural products.