Diisopropylethylamine → 3-{2,5-Dichloro-4-[3-(4-cyclopropyl-3,4-dihydro-2H-quinoxaline-1-carbonyl)-pyridin-4-yloxy]-benzoylamino}-propionic acid ethyl ester

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To a solution of 0.18 g (0.37 mmol) 2,5-dichloro-4-[3-(4-cyclopropyl-3,4-dihydro-2H-quinoxaline-1-carbonyl)-pyridin-4-yloxy]-benzoic acid (Example 29, intermediate) in 2 mL N,N-dimethylformamide were added 0.148 g (0.39 mmol) O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HATU, commercially available, CAS RN 148893-10-1) and 0.25 mL (1.49 mmol) N,N-diisopropylethylamine. To the light brown solution 0.060 g (0.39 mmol) beta-alanine ethylester hydrochloride (commercially available, CAS RN 4244-84-2) was added and the solution was stirred at room temperature for 3.5 hours. The solution was poured on water and extracted three times with ethyl acetate. The combined organic layers were washed twice with water and brine, dried over magnesium sulfate, filtered, treated with silica gel and evaporated. The resulting powder was purified by silica gel chromatography using a MPLC system (10 g silica gel column, CombiFlash Companion, Isco Inc.) with a gradient of n-heptane:ethyl acetate (100:0 to 0:100) to afford 0.185 g (85%) of the title compound as a light brown foam. MS (ESI): m/z=583.15 [M+H]+.

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