To a solution of 6.8 g of the compound of Example 2 in 50 ml of dimethylformamide are added 4.1 g of potassium carbonate and 5 g of 2-bromoethyl acetate, and the mixture is stirred at 60° C. for 16.5 hours. The reaction mixture is poured into ice-cold water, and the precipitate is extracted with ethyl acetate. The extract is washed with water, dried and concentrated, and then the residue is recrystallized from hexane to give 5.9 g of 1-(2-acetoxyethyl)-3-(3,5-di-tertiary butyl-4-hydroxyphenyl)-6-methyl-1H-pyrazolo[-3,4-b]pyridine as pale yellowish green crystals, melting at 101.5°-103° C.
