1: (S)-4-carboxy-2-azetidinone With 2,3,4,5,6-pentafluorophenol; dicyclohexyl-carbodiimide in 1,4-dioxane; N,N-dimethyl-formamide T=0°C; 3.5 h; 2: L-histidinyl-L-prolinamide in 1,4-dioxane; N,N-dimethyl-formamide T=0°C; 2 h;