A solution of (S)-3-cyclopentyl-2-(4-methoxy-2-oxo-2,5-dihydro-pyrrol-1-yl)-propionic acid (prepared as in Example 1, 106 mg, 0.41 mmol) in benzene (10 mL) was treated with oxalyl chloride (55 mg, 0.43 mmol), and N,N-dimethylformamide (1 drop). Effervescence was observed. The reaction mixture was stirred for 2 h at 25° C., under nitrogen. The reaction mixture was concentrated, and dissolved in dichloromethane (10 mL) and treated with pyrazin-2-ylamine (42 mg, 0.43 mmol), and N,N-diisopropylethylamine (161 mg, 1.23 mmol). The reaction mixture was stirred at 25° C., under nitrogen for 18 h. The reaction mixture was diluted with dichloromethane, washed with 2N aqueous hydrochloric acid, saturated sodium chloride solution and dried. The organic layer was concentrated, and the crude product was purified by ISCO flash chromatography (Teledyne Isco RediSep Flash Column 4 g; 0% to 10% methanol/dichloromethane) to afford (S)-3-cyclopentyl-2-(4-methoxy-2-oxo-2,5-dihydro-pyrrol-1-yl)-N-pyrazin-2-yl-propionamide (5 mg, 3%) as a white solid: LR-ES-MS m/z calculated for C17H22N4O3 [M]+ 330, observed [M+H]+ 331; 1H NMR (400 MHz, CDCl3) δ ppm 1.13-1.23 (m, 2H) 1.48-1.98 (m, 8H) 1.98-2.09 (m, 1H) 3.82 (s, 3H) 3.94 (d, J=17.5 Hz, 1H) 4.03 (d, J=17.5 Hz, 1H) 4.83 (dd, J=9.1, 6.5 Hz, 1H) 5.15 (s, 1H) 8.28 (dd, J=2.6, 1.5 Hz, 1H) 8.33 (d, J=2.6 Hz, 1H) 9.09 (s, 1H) 9.47 (d, J=1.5 Hz, 1H).
