Nα -(1,1-Dimethylethoxycarbonyl)-Nε -(2,2,2-trichloroethoxycarbonyl)lysine. In a modification of a literature method [Yajima, H.; Watanabe, H.; Okamoto, M., Studies on peptides. XXXIII. Nε -β,β,β-Trichloroethyloxycarbonyllysine, Chem. Pharm. Bull, 1971, 19, 2185-2189], lysine monohydrochloride (9.14 g, 50 mmol) was stirred under reflux with copper (II) carbonate (21.6 g, 75 mmol) in water (180 mL) for 3 h. The solution was filtered while hot and the filtrate was cooled to 20° C. 2,2,2-Trichloroethyl chloroformate (15.9 g, 75 mmol) and aqueous sodium carbonate (13.3 g, 125 mmol in 40 mL) were added alternately in portions to the filtrate during 30 min and the mixture was stirred vigorously at 0° C. for 20 h. The blue precipitate was collected and was boiled under reflux with ethylenediaminetetraacetic acid disodium salt (18.6 g, 100 mmol) in water (200 mL) for 2 h. The solution was cooled to 0° C. for 20 hrs and crude Nε -(2,2,2-trichloroethoxycarbonyl)lysine was collected as a gummy solid. This material was dissolved in water (75 mL) and triethylamine (20.2 g, 200 mmol) was added, followed by di-t-butyl dicarbonate (13.64 g, 62 mmol) and 1,4-dioxan (30 mL). The mixture was stirred vigorously for 3 d. The mixture was washed with diethyl ether. Ethyl acetate was added to the aqueous phase and the mixture was acidified by careful addition of cold 10% aqueous sulphuric acid. The ethyl acetate phase was washed with water and dried with anhydrous magnesium sulphate. The solvent was evaporated under reduced pressure to give Nα -(1,1-dimethylethoxycarbonyl)-Ne -(2,2,2-trichloroethoxycarbonyl)lysine (12.32 g, 55%).
