A mixture of Nα -Nim -bis-BOC-histidine ethyl acetate solvale (1.92 g, 5.0 mmol), 4-methylmorpholine (0.55 mL, 5.0 mmol) and isobutyl chloroformate (0.65 mL, 5.0 mmol) in ethyl acetate (50 mL) was stirred in an ice bath under N2 for 15 minutes. A solution of (S)-1-ethoxy-2-amino-4-methylpentane (0.73 g, 5.0 mmol) in ethyl acetate (2 mL) was then added and the reaction stirred at room temperature for 20 hours. After washing with 10% citric acid, brine, saturated NaHCO3 solution and brine, the ethyl acetate extract was dried (Na2SO4), filtered and concentrated under reduced pressure. The residue was flash chromatographed over silica gel. Elution with a mixture of 2% methanol and 98% chloroform afforded pure BOC-protected histidineamide (0.90 g).
