To a solution of crude compound (106) (0.4 g, 1.1 mmol) from above and beta-alanine tert-butyl ester hydrochloride (0.2 g, 1.1 mmol) in DMF (5 mL) was added diisopropylethylamine (0.41 mL, 2.3 mmol) followed by O-(benotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (0.44 g, 1.1 mmol). The resulting reaction mixture was stirred at room temperature for 14 h, diluted with ethyl acetate (50 mL), washed with 10% aqueous citric acid solution (30 mL), followed by saturated aqueous NaHCO3 solution (30 mL) and brine (2×20 mL). The organic phase was dried over MgSO4 and concentrated in vacuo. The crude residue was then dissolved in anhydrous dichloromethane (5 mL) and cooled to 0° C. before a solution of hydrochloric acid (1 mL, 4 N in dioxane) was added. The reaction was stirred for 2 h at 0° C. and the solvent was removed in vacuo. The crude residue was purified by preparative LC/MS to afford 50 mg (8% yield over three steps) of the title compound (103). 1H NMR (400 MHz, CDCl3): δ 6 7.85 (dd, J=7.6, 1.6 Hz, 1H), 7.51-7.48 (m, 1H), 7.34-7.13 (m, 5H), 3.72 (q, J=6.0 Hz, 2H), 3.13-3.10 (m, 2H), 2.67 (t, J=6.4 Hz, 2H), 1.25 (d, J=6.8 Hz, 12H). MS (ESI) m/z 414.3 (M+H+).
