N-Cbz-glycine (339 mg, 1.62 mmol) was dissolved in 8 mL EtOAc, cooled to -15° C., then NMM (196 μL, 1.8 mmol) and isobutyl chloroformate (230 μL, 1.8 mmol) were added. After 20 min, the mixed anhydride solution was added to amine 3-4 (0.50 mg, 1.6 mmol) suspended in 5 niL EtOAc and the reaction was warmed to RT for 90 min. Following dilution with EtOAc, the mixture was washed with water, sat. NaHCO3, 5% KHSO4, and brine, dried (MgSO4), filtered and concentrated. Flash chromatography (silica, 75% EtOAc/hexane) provided amide 3-5 as a colorless oil.
