A mixture of 2-(acetylamino)-4-(2-{4-[(tert-butoxycarbonyl)amino]phenyl}ethyl)-1,3-thiazole-5-carboxylic acid (80.mg), aniline (0.019 ml), benzotriazole-1-yl-oxy-tris-pyrrolidino-phosphonium hexafluorophosphate (113 mg) and N,N-diisopropylethylamine (0.076 ml) in N,N-dimethylformamide (2 ml) was stirred at ambient temperature for 21 hours and at 55 ° C. for 3 hours. The reaction mixture was poured into 1N hydrochloric acid, and extracted with chloroform. The organic layer was washed with water, saturated sodium hydrogen carbonate solution and saturated sodium chloride solution, dried over anhydrous magnesium sulfate, and concentrated in vacuo. The residual solid was washed with ethyl ether to give tert-butyl 4-{2-[2-(acetylamino)-5-(anilinocarbonyl)-1,3-thiazol-4-yl]ethyl}phenylcarbamate (57.2 mg) as a colorless solid.
