Hydrochloric Acid → 2-[2-(2-acetylamino-ethylcarbamoyl)-ethyl]-4-methyl-1H-pyrrole-3-carboxylic acid ethyl ester

5-[2-(2-Acetylamino-ethylcarbamoyl)-ethyl]-3-methyl-1H-pyrrole-2,4-dicarboxylic acid 2-tert-butyl ester 4-ethyl ester 62a (818 mg, 2 mmol) was dissolved in 5 ml of ethanol under stirring, and added with hydrochloric acid solution (5 ml, 12 mol/L) to the solution at room temperature. Upon completion of the addition, the reaction mixture was heated at 60° C. in an oil bath for 2 hours. After thin lay chromatography showed the disappearance of starting materials, the reaction mixture was concentrated under reduced pressure to evaporate ethanol, adjusted to about pH 12 with aqueous sodium hydroxide solution (10%) and extracted with ethyl acetate (20 ml×3). The combined organic extracts were dried over anhydrous magnesium sulfate, filtered to remove the drying agent and concentrated under reduced pressure to obtain the title compound 2-[2-(2-acetylamino-ethylcarbamoyl)-ethyl]-4-methyl-1H-pyrrole-3-carboxylic acid ethyl ester 62b (600 mg, yield 97%) as a white solid.