1: Boc-L-Val-SH With caesium carbonate in N,N-dimethyl-formamide T=20°C; 0.0833333 h; 2: (S)-(-)-tryptophan methyl ester hydrochloride With 1-fluoro-2,4-dinitrobenzene in N,N-dimethyl-formamide T=20°C; 3 h;

caesium carbonate in N,N-dimethyl-formamide T=20°C; 1 h;

N'-(3-dimethylaminopropyl)-N-ethylcarbodiimide in dichloromethane 24 h; Ambient temperature;