Reaction Steps
A stirred solution of [3S/R, 4S/R, (2R)]-3-[2-(2-carbazol-9-yl-2-oxo-ethyl)-pentanoylamino]-5-fluoro-4-hydroxy-pentanoic acid tert-butyl ester (2.51 g, 5.03 mmol) in anhydrous DCM (60 ml) was treated with 1,1,1-triacetoxy-1,1-dihydro-1,2-benziodoxol-3 (1H)-one (2.35 g, 5.53 mmol) at 0° C. The resulting mixture was kept at 0° C. for 3 h, diluted with DCM, and then washed sequentially with saturated aqueous sodium thiosulphate, NaHCO3 solution and brine. The organics were dried (Na2SO4) and concentrated. The residue was purified by flash chromatography (25% ethyl acetate in 40/60 hexanes) to afford the sub-title compound as an off white solid (1.437 g, 57%): IR (solid, cm−1) 1722, 1689, 1636, 1531, 1441, 1365, 1279, 1155; 1H NMR (400 MHz, CDCl3) δ 0.85-1.50 (3H, m), 1.35-1.54 (11H, m), 1.55-1.69 (1H, m), 1.78-1.95 (1H, m), 2.67-3.28 (4H, m), 3.60-3.79 (1H, m), 4.80-5.59 (3H, m), 6.89-7.04 (1H, m), 7.33-7.54 (4H, m), 7.98-8.04 (2H, m), 8.15-8.28 (2H, m); 13C (100 MHz, CDCl3) δ 14.12, 14.40, 14.47, 14.60, 20.78, 20.84, 21.47, 28.32, 28.42, 28.48, 29.77, 33.63, 34.58, 34.91, 40.05, 43.05, 43.26, 43.29, 52.60, 53.00, 53.64, 66.90, 66.99, 82.62, 82.69, 85.53, 116.88, 116.94, 120.28, 120.31, 124.27, 127.76, 127.86, 128.69, 128.77, 128.99, 138.80, 171.21, 171.29, 172.21, 172.25, 175.53, 176.03, 203.04, 203.20, 203.30, 203.46; 19F (376 MHz, CDCl3) δ −232.12, −233.24.
