To a solution of 5.2 g of the compound of Example 43 in 30 ml of chloroform is added 2.1 g of triethylamine, and the mixture is cooled and then stirred. To the reaction mixture is added dropwise 1.7 g of acetyl chloride below 0° C. over 5 minutes. After completion of the addition, the mixture is stirred at room temperature for 3 hours, and the reaction solution is washed with water, dried and concentrated. The residue is recrystallized from isopropyl alcohol to give 5 g of 1-(2-acetoxyethyl)-3-(3,5-di-tertiary butyl-4-hydroxyphenyl)-1H-pyrazolo[3,4-b]pyridine as white crystals, melting at 115°-116° C.
