Reaction Steps
A solution of [3S/R, (2R)]-3-[2-(2-carbazol-9-yl-2-oxo-ethyl)-pentanoylamino]-5-fluoro-4-oxo-pentanoic acid tert-butyl ester (1.43 g, 2.88 mmol) in anhydrous DCM (20 ml) was treated with a solution of TFA (10 ml) in anhydrous DCM (10 ml) with stirring. The mixture was stirred at 0° C. for 2 h then at room temperature for 2 h. The mixture was concentrated under reduced pressure and then the residue was dissolved in dry DCM. This process was repeated several times in order to remove excess trifluoroacetic acid. The off-white solid was recrystallized from Et2O/40/60 hexanes to give the title compound as a white powder (71 mg): IR (solid, cm−1) 1746, 1689, 1641, 1541, 1436, 1374, 1284, 1207, 1160 cm−1; 1H NMR (400 MHz, d6-DMSO) δ 0.80-1.00 (3H, m), 1.20-1.76 (4H, m), 2.30-2.90 (2H, m), 2.95-3.24 (1H, m), 3.26-3.59 (2H, m), 4.25-4.79 (1.5H, m), 5.02-5.43 (1.5H, m), 7.36-7.58 (4H, m), 8.10-8.30 (4H, m), 8.54-8.91 (1H, m); 13C NMR (100 MHz, DMSO) δ 14.31, 20.03, 20.13, 21.92, 22.51, 34.36, 34.77, 41.20, 41.62, 44.06, 51.77, 52.84, 83.45, 85.22, 116.70, 120.54, 123.91, 124.01, 127.85, 126.01, 138.20, 172.15, 172.36, 172.96, 173.00, 175.32, 175.48, 202.60, 203.10; 19F (376 MHz, DMSO) δ −226.68, −226.73, −231.21, −232.95, −233.38, −233.52.
