Screening, and identification of the binding position, of xanthine oxidase inhibitors in the roots of Lindera reflexa Hemsl using ultrafiltration LC–MS combined with enzyme blocking

A method based on enzyme blocking combined with ultrafiltration liquid chromatography–mass spectrometry (LC–MS) has been developed to identify xanthine oxidase (XOD) inhibitors in the roots of Lindera reflexa Hemsl (LR) and determine their binding positions. Allopurinol and febuxostat, known XOD inhibitors, which occupy different binding positions in XOD, were used as blockers and pre‐incubated with XOD. Then the LR extract was incubated without XOD, and with XOD, allopurinol‐blocked XOD and febuxostat‐blocked XOD before ultrafiltration LC–MS was performed. By comparing the chromatographic profiles of the incubation samples, not only the ligands, but also the binding position of these ligands with XOD could be determined. Finally, three compounds, pinosylvin, pinocembrin and methoxy‐5‐hydroxy‐ trans ‐stilbene, were identified as potential XOD inhibitors and the binding modes of these three compounds were shown to be similar to those of febuxostat. To verify the XOD inhibitory activity of the screened compounds, the microplate method and molecular docking in silico were used to evaluate the enzyme inhibitory activities and the binding positions with XOD. The results showed that the developed method could screen for XOD ligands in LR extracts and also determine the binding positions of the ligands. To our knowledge, this is the first report of the XOD inhibitory activity of these three compounds.