N-ethyl-N,N-diisopropylamine in N,N-dimethyl-formamide T=20°C; Acylation; 2 h;

potassium carbonate in 1,4-dioxane Ambient temperature;

1: N-(fluoren-9-ylmethoxycarbonyl)-L-Lys(Nε-Boc) With trifluoroacetic acid in dichloromethane T=20°C; 2 h; 2: carbonic acid 4-nitro-phenyl ester 2-trimethylsilanyl-ethyl ester With N-ethyl-N,N-diisopropylamine in N,N-dimethyl-formamide T=20°C; 16 h;

1: CF3COOH / CH2Cl2 / 0.33 h / 20 °C 2: 95 percent / iPr2NEt / dimethylformamide / 2 h / 20 °C View Scheme