To a suspension of 1,1′-carbonyldiimidazole (1.95 g) in methylene chloride (20 ml) was added tert-butyl N-(2-aminoethyl)carbamate (1.92 g) under ice-cooling, and the mixture was stirred at room temperature for 2 hours. To the reaction mixture were added N-ethyldiisopropylamine (2.59 g) and 7-amino-2,3-dihydro-1H-imidazo[1,2-b]pyrazole sulfuric acid salt (2.22 g), and the mixture was stirred at room temperature for 16 hours. To the reaction mixture were added trityl chloride (9.0 g) and triethylamine (3.0 g). The mixture was stirred at room temperature for 24 hours. The reaction mixture was washed with 10% aqueous citric acid solution, brine and saturated aqueous sodium hydrogen carbonate solution. The organic layer was dried over anhydrous magnesiumsulfate, filtered and concentrated in vacuo. The residue was purified by column chromatography on silica gel eluting with 3% methanol/chloroform to give 7-(3-{2-[(tert-butoxycarbonyl)amino]ethyl}ureido)-2,3-dihydro-1-tritylimidazo[1,2-b]pyrazole (800 mg) as a solid.
