The general procedure for the synthesis of N2-(tert-butoxycarbonyl)-N6-(2,2,2-trifluoroacetyl)-D-lysine from di-tert-butyl dicarbonate and trifluoroacetyl-lysine was as follows: trifluoroacetyl-lysine (3.63 g, 0.015 mol) was suspended in 40 ml of N,N-dimethylformamide (DMF), to which was added triethylamine (TEA, 3.03 g , 0.03 mol) and di-tert-butyl dicarbonate (3.6 g, 0.0165 mol). The reaction mixture was stirred at room temperature for 3 hours. After completion of the reaction, the mixture was diluted with water to three times the original volume and acidified with hydrochloric acid to pH 2. The product was extracted with ethyl acetate (EtOAc, 100 ml), the organic phase was washed with water and saturated brine sequentially and dried with anhydrous magnesium sulfate (MgSO4). The solvent was removed by distillation under reduced pressure to afford (S)-2-((tert-butoxycarbonyl)amino)-6-(2,2,2-trifluoroacetamido)hexanoic acid (4.7 g, 92% yield). The analytical data of the product (3) were in agreement with literature reports.
