C(CC(O)=O)C.[C:7]([N:14](C(OC(C)(C)C)=O)[C@H:15]([C:22]([OH:24])=O)[CH2:16][C:17]1[N:21]=[CH:20][NH:19][CH:18]=1)([O:9][C:10]([CH3:13])([CH3:12])[CH3:11])=[O:8].C[N:33]1CCOCC1.ClC(OCC(C)C)=O.N[C@@H](CC(C)C)CSCC>C(OCC)(=O)C>[C:7]([NH:14][C@H:15]([C:22]([NH2:33])=[O:24])[CH2:16][C:17]1[N:21]=[CH:20][NH:19][CH:18]=1)([O:9][C:10]([CH3:11])([CH3:12])[CH3:13])=[O:8]A mixture of NαNim -bis BOC-(S)-histidine ethyl acetate solvate (0.96 g, 2.50 mmol), 4 methyl-morpholine (0.28 mL, 2.50 mmol) and isobutyl chloroformate (0.33 mL, 2.50 mmol) in ethyl acetate (35 mL) is stirred in an ice bath under N2 for 15 minutes. A solution of (S)-2-amino-1-ethylthio-4-methyl pentane (0.40 g, 2.50 mmol) in ethyl acetate (2 mL) is then added and the reaction stirred at room temperature for 18 hours. After washing with 10% citric acid, brine, saturated NaHCO3 solution and brine, the ethyl acetate extract is dried (Na2SO4), filtered and concentrated under reduced pressure. The residue is flash chromatographed over silica gel. Elution with a mixture of 2% methanol- 98% chloroform affords pure BOC-protected histidineamide.
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