5.8 g of 5-(1-hydroxy-2-isopropylaminobutyl)-8-hydroxycarbostyril was dissolved in 100 ml of methanol, and a methanolic solution of 10% sodium methylate was added to the resulting solution in an equimolar amount relative to the starting carbostyril compound. The mixture was concentrated to dryness and the resulting residue was dissolved in 100 ml of dimethylformamide. 2.9 g of cyclohexanecarboxylic acid chloride was then added while cooling with ice-water and the mixture was stirred for one hour at a temperature of 0° C. The precipitate formed was separated by filtration and washed successively with dimethylformamide and diethyl ether to obtain 4.0 g of 8-cyclohexylcarbonyloxy-5-(1-hydroxy-2-isopropylaminobutyl)carbostyril having a melting point of 186.5°-187.5° C. (after recrystallization from chloroform-diethyl ether).
