2-(Acetylamino)-4-[2-(4-aminophenyl)ethyl]-1,3-thiazole-5-carboxylic acid (106 mg) was suspended in THF (2 ml) under N2 atmosphere. Bis(trimethylsilyl)acetamide (0.253 ml) was added to the suspension at r.t., and the mixture was stirred at r.t. for 15 minutes. Then, N,N′-bis(tert-butoxycarbonyl)-1H-pyrazole-1-carboxamidine (119 mg) was added to the solution at r.t. The reaction mixture was stirred at r.t. for 20 hours, and concentrated in vacuo. The residue was dissolved in CHCl3. The organic solution was washed with 1N—HCl, water and brine, dried over anhydrous MgSO4, and concentrated in vacuo. The residual solid was washed with ethyl ether to give 2-(acetylamino)-4-{2-[4-({(Z)-[(tert-butoxycarbonyl)amino](tert-butoxycarbonyl)iminomethyl}amino)phenyl]ethyl}-1,3-thiazole-5-carboxylic acid (115.8 mg) as a pale brown solid.
