1 N Aqueous sodium hydroxide (2.6 mL) was added to a solution of benzyl 3-benzyloxy-2-benzyloxymethyl-2-methylpropionate obtained in Step A (350 mg, 0.87 mmol) in THF (2.6 mL), and the mixture was stirred under reflux for three hours. Water and ethyl acetate were added to the mixture to separate the aqueous layer. 1 N hydrochloric acid was added to the aqueous layer to make the aqueous layer acidic, followed by extraction with ethyl acetate. The extract was dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure. From the resulting residue, crude 3-benzyloxy-2-benzyloxymethyl-2-methylpropionic acid (95 mg) was obtained as a colorless oil without purification. Condensation was carried out by a method similar to that of Example 3-1 using 3-benzyloxy-2-benzyloxymethyl-2-methylpropionic acid obtained above instead of Boc-Sar-OH and 7-((S)-5-hydroxymethyl-2-oxooxazolidin-3-yl)-3-(2-trifluoromethylphenyl)-2H-isoquinolin-1-one obtained in Step B of Example 1-13 instead of 7-((R)-5-hydroxymethyl-2-oxooxazolidin-3-yl)-3-(2-trifluoromethylphenyl)-2H-isoquinolin-1-one obtained in Step B of Example 1-14, and deprotection was carried out by a method similar to that of Example 1-36 using a 10% Pd—C catalyst in a hydrogen atmosphere to synthesize the title compound.
