To a solution of 2.7 g 4-Hydroxy-quinoline-2-carboxylic acid and 5 g of 4-((S)-2-Amino-4-tert-butoxycarbonyl-butyryl)-piperazine-1-carboxylic acid ethyl ester in 25 ml of DMF, 2.2 g of HOBT and 2.8 g of EDC was added and the reaction mixture was stirred for 3 h at RT. Then, the reaction mixture was diluted with water and extracted with DCM. The organic phase was dried over MgSO4 and the solvents were removed under reduced pressure. The crude product was purified by re-crystallisation from n-heptane/ethyl acetate and dried under reduced pressure. Yield: 7.2 g.
