To a solution of 2-adamantyloxycarbonyl-α-methyl-DL-tryptophan (0.401 g, 1.01 mmol) in dry ethyl acetate (6 mL) and N,N-dimethylformamide (4 mL) under nitrogen atmosphere was added pentafluorophenol (0.189 g, 1.03 mmol) followed by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (0.200 g, 1.04 mmol). This mixture was stirred 2 hours, then triethylamine (0.36 mL, 2.6 mmol) and histamine dihydrochloride (0.240 g, 1.30 mmol) were added. After stirring an additional 40 hours, the resulting mixture was diluted with ethyl acetate (20 mL), and washed with water. The organic phase was dried over MgSO4, concentrated, purified by flash chromatography (SiO2, 4×20 cm, 230-400 mesh, 10% methanol/dichloromethane eluant), and dried for 48 hours under vacuum at 70° C. to provide 0.234 g (47%) of product; 1H NMR (CDCl3) δ1.40-1.60 (2H, m), 1.57 (3H, s), 1.65-2.00 (13H, m), 2.65-2.75 (2H, m), 3.25-3.45 (4H, m), 4.82 (1H, br s), 5.42 ([H, br s), 6.67 (1H, s), 6.81 (1H, br s), 6.91 (1H, br s),7.00-7.20 (2H, m), 7.34 (1H, d, J 7 Hz), 7.46 (1H, s), 7.55 (1H, d, J 7 Hz), 8.67 (1H, br s).
