1.4) Compound F1 (13.8 g, 95.0 mmol) and sodium hydroxide (7.6 g, 190.08 mmol) were added sequentially to a mixture of ethanol (200 mL) and water (1:1 by volume) and heated to reflux for 4 hours. Upon completion of the reaction, the pH of the reaction mixture was adjusted to 7 with 2 M hydrochloric acid solution, followed by evaporation of the solvent. The residue was dissolved in a small amount of water and purified by strongly acidic cation exchange resin 732. The final product G1 (10 g, 90% yield) was obtained as a white solid.
