Reaction Steps
To a stirred solution of 40.1 mg (0.09 mmol) of 8 in 5 mL of dry CH2Cl2 was added sequentially 140 mg (0.37 mmol) of O-(7-azabenzotriazole-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HATU), 49.5 mg (0.37 mmol) of HOBt, and 91 uL (0.55 mmol) of DIEA. The resulting solution was stirred at room temperature for 10 min followed by adding 50.5 mg (0.18 mmol) of O-tritylhydroxylamine. After stirring at the same temperature for 30 min, the solvent was removed in vacuo and the residue was purified by flash chromatography (EtOAc/Hex 1:4) to give O-trityl hydroxyamic acid of 8 in a quantitative yield. The resulting oily product was treated with 5 mL of 1:2 mixture of AcOH/2,2,2-trifluoroethanol at room temperature for 24 h. After evaporation of the solvent in vacuo, the residue was dissolved in CH2Cl2 and washed with 10 mL of a saturated NaHCO3 solution. The organic layer was dried over MgSO4, filtered, and concentrated in vacuo. The residue was purified by flash chromatography (MeOH/EtOAc 1:9) to give 12.7 mg (54% over two steps) of 9 as a bright yellow powder: mp˜150° C. (decomp); 1H NMR (400 MHz, DMSO-d6) δ 12.1 (s, 1H), 11.68 (brs, 1H), 8.95 (brs, 1H), 7.99 (s, 1H), 7.93 (d, J=7.8 Hz, 2H), 7.81 (s, 1H), 7.70 (m, 3H), 7.66-7.48 (m, 6H), 7.38 (t, J=7.0 Hz, 1H), 7.08 (s, 1H), 3.41 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 187.4, 167.1, 147.9, 142.3, 141.6, 138.1, 136.9, 133.3, 133.2, 132.8, 132.1, 131.4, 131.0, 129.8, 129.7, 129.0, 127.7, 126.2, 121.1, 120.7, 113.9, 99.9, 33.2; IR (KBr) cm−1 3422-3241, 2902, 1596, 1433, 1322.
