1: N-Boc-5-allyl-L-proline methyl ester With hydrogenchloride in 1,4-dioxane; methanol T=20°C; 2: Nα-Boc-Nβ-Cbz-amino-L-alanine With benzotriazol-1-ol; 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride; N-ethyl-N,N-diisopropylamine in dichloromethane T=20°C;

1: N-Boc-5-allyl-L-proline methyl ester With hydrogenchloride in 1,4-dioxane; methanol T=20°C; 2: Nα-Boc,Nβ-Z-Dap*DCHA With benzotriazol-1-ol; 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride; N-ethyl-N,N-diisopropylamine in dichloromethane T=20°C; Product distribution / selectivity;

1.1: hydrogenchloride / 1,4-dioxane; methanol / 20 °C 1.2: 20 °C 2.1: triphenylphosphine; ozone / dichloromethane View Scheme

1: 1.) O3; 2.) NaBH4 / 1.) MeOH, CH2Cl2, -78 deg C; 2.) MeOH, CH2Cl2, -78 deg C to RT 2: (n-Bu)3P / tetrahydrofuran 3: 1.) MCPBA; 2.) Me2S, Et3N / 1.) CH2Cl2, -70 deg C, 30 min; 2.) CH2Cl2, -70 deg C to RT 4: TFA / CH2Cl2 View Scheme

thionyl chloride in methanol T=20°C; 18 h;