A solution of 3-cyclopentyl-2-(4-methoxy-6-oxo-6H-pyridazin-1-yl)-propionic acid (100 mg, 0.37 mmol) in methylene chloride (2.08 mL, 0.18M) at 25° C. was treated with N,N,N′,N′-tetramethyl-O—(N-succinimidyl)uronium tetrafluoroborate (135.6 mg, 0.45 mmol) and N,N-diisopropylethylamine (0.196 mL, 1.12 mmol). The resulting solution was stirred at 25° C. for 2 h. After this time, the reaction was treated with thiazol-2-ylamine (49 mg, 0.48 mmol). The resulting solution was stirred at 25° C. for 1 d. After this time, the reaction was partitioned between water (75 mL) and methylene chloride (3×75 mL). The combined organics were dried over sodium sulfate, filtered and concentrated in vacuo. Silica gel column chromatography (ISCO, 40 g, 1% methanol/methylene chloride) afforded 3-cyclopentyl-2-(4-methoxy-6-oxo-6H-pyridazin-1-yl)-N-thiazol-2-yl-propionamide as a white solid (41.4 mg, 32%); ES+-HRMS m/e calcd for C16H20N4O3S [M+H+] 349.1329, found 349.1328. 1H-NMR (300 MHz, DMSO-d6) δ ppm 0.98-7.78 (m, 9H), 1.95 (m, 1H), 2.27 (m, 1H), 3.82 (s, 3H), 5.54 (dd, J=4.5, J=10.6 Hz, 1H), 6.32 (d, Jm=2.7 Hz, 1H), 7.23 (d, J=3.6 Hz, 1H), 7.48 (d, J=3.6 Hz, 1H), 7.88 (d, Jm=2.7 Hz, 1H), 12.53 (s, 1H).
