To a solution of Boc-L-propargylglycine (26.65 g; 125 mmol) in dry DMF (170 mL) was added EDCI (29.23 g; 152.5 mmol) and HOBt (23.5 g; 122.5 mmol), and the reaction mixture was stirred at room temperature for 40 min (solution A). In a separate RB flask, (L) Leu-OMe hydrochloride (22.72 g; 125 mmol) in dry DMF (82 mL) kept at 0° C. was treated with diisopropyl ethyl amine (DIEA) (64.62 g; 500 mmol) and the solution was stirred for 25 min (solution B). Solution B was added to solution A and the reaction mixture was stirred overnight at room temperature. The solvent was removed on the rotary evaporator and the residue was taken up in dichloromethane (DCM) (600 mL) and washed sequentially with saturated sodium bicarbonate (2×200 mL), 5% HCl (2×200 mL) and brine (200 mL). The organic layer was dried over anhydrous sodium sulfate, filtered and concentrated, leaving a crude product which was purified using flash chromatography (silica gel; hexane/ethyl acetate 75:25) to give 1 as a white solid (38.12 g; 89% yield); 1H NMR (CDCl3) δ 8.2 (s, 1H), 7.0 (s, 1H), 4.3 (m, 1H), 4.1 (m, 1H), 3.6 (s, 3H), 2.8 (s, 1H), 2.4 (m, 2H), 2.3 (m, 1H), 1.6 (m, 2H), 1.5 (m, 1H), 1.38 (s, 9H), 0.87 (d, 6H).
