A solution of 133 mg (0.4 mmol) of (3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoic acid (Intermediate 3), 84.5 mg (0.44 mmol) of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and 71 mg (0.5 mmol based on 95% purity) of 1-hydroxybenzotriazole (HOBT) in 1.5 mL of anhydrous DMF was stirred at room temperature in a stoppered flask. After 15 min, this solution was added dropwise by syringe through a septum to a stirred suspension of 72.1 mg (0.48 mmol) of 5-hydrazino[1,2,4]triazolo[1,5-c]pyrimidine (Intermediate 20) 0.209 mL (155 mg, 1.2 mmol) of N,N-diisopropylethylamine in 1 mL of anhydrous DMF. Stirring under nitrogen was continued for 17 h. The mixture was then filtered and concentrated under vacuum. The residue was partitioned between ethyl acetate and 5% aqueous citric acid solution. The organic phase was washed with more 5% citric acid, then with water, and finally with saturated aqueous sodium carbonate solution. The organic solution was dried over magnesium sulfate, filtered and concentrated to yield the title compound as an off-white solid, mp 207.5-209.5° C. LC-MS 488 (M+Na), 366 (M+1-Boc).
