General procedure: 20 g (42 mmol) of methyl (2S,3S,4S,5R,6S)-6-((5,6-dihydroxy-2-(4-hydroxyphenyl)-4-yloxy-4H-benzopyran-7-yl)oxy)-3,4,5-trihydroxytetrahydro-2H-pyran-2-carboxylate was dissolved in a mixed solvent of 300 mL of water and 300 mL of acetone at 0 °C Stirring. Under the protection of nitrogen, 70 mL of 10% aqueous sodium hydroxide solution was slowly added dropwise, and the reaction temperature was maintained at 0 °C with continuous stirring for about 2 h. The reaction process was monitored by HPLC. After the reaction was completed, 10% hydrochloric acid aqueous solution was slowly added dropwise under stirring to adjust the pH of the reaction solution to 2.0-3.0, and stirring was continued for 1 hour. Subsequently, the reaction system was gradually brought to room temperature and a large amount of yellow solid 5,6,4'-trihydroxyflavone-7-yloxy-glucuronic acid was observed to precipitate gradually. The reaction mixture was allowed to stand at room temperature overnight, followed by diafiltration and the filter cake was washed with appropriate amount of water and acetone and dried. Finally, purification by ethanol recrystallization afforded 17.3 g of pure 5,6,4'-trihydroxyflavone-7-yloxy-glucuronic acid in 89% yield. The purity of the product was 98.74% by HPLC, and its HPLC chromatogram is shown in Fig. 1, and the statistical results are shown in Table 1.1H-NMR (400 MHz, DMSO) data were as follows: δ 10.41 (1H, s), 8.63 (1H, s), 7.94 (2H, d, J = 8.8Hz), 6.99 (1H, s), 6.94 (2H, d, J = 8.8Hz), 6.99 (1H, s), 6.94 (2H, d, J = 8.8Hz). d, J = 8.8 Hz), 6.86 (1H, s), 5.51-5.31 (3H, br), 5.28 (1H, d, J = 7.5 Hz), 4.11 (2H, d, J = 9.6 Hz), 3.43 (4H, m).
