1: iodine / tetrahydrofuran; water / 12 h / 20 °C 2: sodium carbonate / tetrahydrofuran View Scheme

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;