To a solution of 3.5 g of 4-{(S)-4-tert-Butoxycarbonyl-2-[(4-carboxymethoxy-7-methyl-quinoline-2-carbonyl)-amino]-butyryl}-piperazine-1-carboxylic acid ethyl ester in 30 ml of DMF, 1.1 g of EDC, 1.1 g of pentafluorophenol and 1.8 g of NEM was added and the reaction mixture was warmed to 40° C. for 4 h. Then, after cooling to RT 2.6 g of (S)-Pyrrolidine-2-carboxylic acid cyclobutylamide trifluoroacetate and 1 g of NEM in 10 ml of DMF was added. After 4 h the reaction mixture was diluted with water and extracted with DCM (3×150 ml). The combined organic phases were dried over MgSO4 and the solvents were removed under reduced pressure. The crude product was purified by chromatography on silica gel eluting with a gradient of n-heptane/ethyl acetate. The fractions containing the product were combined and the solvent evaporated under reduced pressure. Yield: 1.8 g.
