in methanol T=70°C; 48 h;

1: (S)-3-(benzyloxycarbonyl)amino-2-hydroxyhexanoic acid With 1-hydroxy-pyrrolidine-2,5-dione; 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride in N,N-dimethyl-formamide T=-9.8 - 20°C; 3 h; Cooling with acetone-dry ice; 2: anhydrous cyclopropylamine in N,N-dimethyl-formamide T=-10 - 20°C;

1.1: hydrogenchloride / 6 h / |Reflux; |Inert atmosphere 2.1: potassium carbonate / water; tetrahydrofuran / 4 h / 20 °C 2.2: 2 h / 10 - 25 °C 3.1: N-ethyl-N,N-diisopropylamine; sulfur trioxide pyridine complex / toluene; dimethyl sulfoxide / 1 h / 0 °C / |Inert atmosphere 3.2: 1 h / 0 °C 4.1: water; sodium dithionite / methanol / 0 °C / |Cooling 4.2: 2 h / 25 °C 5.1: hydrogenchloride; water / 3 h / |Reflux 5.2: |Reflux 5.3: 3 h / 10 - 20 °C 6.1: methanol / 48 h / 70 °C View Scheme

1.1: N-ethyl-N,N-diisopropylamine; sulfur trioxide pyridine complex / toluene; dimethyl sulfoxide / 1 h / 0 °C / |Inert atmosphere 1.2: 1 h / 0 °C 2.1: water; sodium dithionite / methanol / 0 °C / |Cooling 2.2: 2 h / 25 °C 3.1: hydrogenchloride; water / 3 h / |Reflux 3.2: |Reflux 3.3: 3 h / 10 - 20 °C 4.1: methanol / 48 h / 70 °C View Scheme

1.1: water; sodium dithionite / methanol / 0 °C / |Cooling 1.2: 2 h / 25 °C 2.1: hydrogenchloride; water / 3 h / |Reflux 2.2: |Reflux 2.3: 3 h / 10 - 20 °C 3.1: methanol / 48 h / 70 °C View Scheme