To a solution of (3-chloropyrazin-2-yl)methanamine.HCl (9.57 g, 21.26 mmol, 40% wt) and Z-Pro-OH (5.3 g, 21.26 mmol) in dichloromethane (250 mL) was added triethylamine (11.85 mL, 85 mmol) and the reaction mixture was cooled to 0° C. After 15 min stirring at 0° C., HATU (8.49 g, 22.33 mmol) was added. The mixture was stirred for 1 hour at 0° C. and then overnight at room temperature. The mixture was washed with 0.1 M HCl-solution, 5% NaHCO3, water and brine, dried over sodium sulfate and concentrated in vacuo. The product was purified using silica gel chromatography (heptane/ethyl acetate=1/4 v/v %) to give 5 g of (S)-benzyl 2-((3-chloropyrazin-2-yl)methylcarbamoyl)pyrrolidine-1-carboxylate (62.7%).
