In a 100 ml, three-necked flask fitted with a magnetic stirrer, under inert atmosphere, ethyl 4-aminobutanoate hydrochloride al 7 (1.75 g, 0.0104 mol) is dissolved in MeOH (30 ml). Sodium acetate (1.28 g, 0.0156 mol), a solution of 1-(1-trityl-1H-imidazol-4-yl)propan-1-one x89 (0.96 g, 2.6 mmol) in a mixture of MeOH (7 ml) and Et2O (20 ml), NaBH3CN (0.15 g, 2.34 mmol) and finally Na2SO4 are added. After stirring for 48 h at room temperature, the mixture is poured on Et2O/H2O. The organic phase is washed with water and brine, dried over Na2SO4, filtered and concentrated in vacuo. The crude ethyl 4-{[1-(1-trityl-1H-imidazol-4-yl)propyl]amino}butanoate x90 (0.814 g) is used in the next step without any further purification.
