A solution of the title compound of Example 1, (2R)-(4′-chlorobiphenyl-4-sulfonylamino)-5-(1,3-dioxo-1,3-dihydroisoindol-2-yl)pentanoic acid (304 mg, 0.593 mmol) and NMM (0.330 mL, 3.00 mmol) in 10 mL of dichloromethane is treated with 1-hydroxy-7-azabenzotriazole (89 mg, 0.654 mmol) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (170 mg, 0.886 mmol) at RT. After stirring for 30 min, O-tritylhydroxylamine (489 mg, 1.776 mmol) is added, and the reaction is stirred for 16 h. The mixture is partitioned between 60 mL of dichloromethane and 40 mL of water. The organic solution is washed with 30 mL of 1 M aqueous NaHCO3, dried over anhydrous Na2SO4 and concentrated. Chomatography on silica gel (eluant; 4/6—ethyl acetate/hexane) affords 293 mg (64%) of (2R)-(4′-chlorobiphenyl-4-sulfonylamino)-5-(1,3-dioxo-1,3-dihydroisoindol-2-yl)pentanoic acid O-tritylhydroxyamide as a waxy solid: NMR(CDCl3) 0.62-0.76 (br m, 1H), 1.08-1.24 (br m, 1H), 1.46-1.65 (br m, 1H), 1.72-1.87 (br m, 1H), 3.65-3.73 (m, 2H), 3.94 (t, 1H, J=8.7), 5.31 (d, 1H, J=9.2), 7.20-7.27 (m, 15H), 7.48 (d, 4H, J=8.4), 7.59 (d, 2H, J=8.5), 7.70 (d, 4H, J=8.3), 7.91 (d, 2H, J=8.3), 8.27 (s, 1H); IR 1770, 1710, 1349, 1166; ESI-MS 770 (M++1).
