Triethylamine (0.30 mL, 2.18 mmol) was added to a solution of (R)—N-Boc-4-chlorophenylalanine (392 mg, 1.31 mmol), 3-piperazin-1-yl-imidazo[1,2-a]pyridine dihydrochloride (300 mg, 1.09 mmol), and 1-hydroxybenzotriazole (177 mg, 1.31 mmol) in DMF (5 mL) followed by the addition of 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (251 mg, 1.31 mmol) in a single portion. After being stirred for 12 hours, the mixture was diluted with H2O, basified to pH 12 with 1.0 M NaOH, and extracted with DCM. The DCM extracts were dried (Na2SO4), filtered, and concentrated in vacuo. The residue was chromatographed (SiO2) using DCM:Et2O (1:1) followed by 10% MeOH/DCM as eluent to give (R)-[1-(4-chlorobenzyl)-2-(4-imidazo[1,2-a]pyridin-3-yl-piperazin-1-yl)-2-oxo-ethyl]-carbamic acid tert-butyl ester (350 mg).
