To a solution of 150 mg 4-[(S)-4-Carboxy-2-({5-[2-((S)-2-cyclobutylcarbamoyl-pyrrolidin-1-yl)-2-oxo-ethoxy]-1-phenyl-1H-pyrazole-3-carbonyl}-amino)-butyryl]-piperazine-1-carboxylic acid ethyl ester in 7 ml acetone were added 40 mg chloromethylpivalate, 8 mg tetrabutylammonium iodide, 72 mg cesium carbonate and 61 μl triethylamine. The reaction mixture was refluxed for 4 h under argon. Additional 40 mg chloromethylpivalate, 8 mg tetrabutylammonium iodide, 72 mg cesium carbonate and 61 μl triethylamine were added and the suspension refluxed for another 7 h. The reaction mixture was concentrated and the residue was purified by preparative HPLC (C18 reverse phase column, elution with a water/MeCN gradient with 0.1% TFA). The fractions containing the product were lyophilized to yield the pure product. Yield: 75 mg MS (ES+): m/e=796.
