To a solution of (S)-tert-butyl 3-methylpiperazine-1-carboxylate (0.10 g, 0.50 mmol) in N,N-dimethylformamide (5 mL) was added O-(7-azabenzotriazol-1-yl)-N,N,N,N-tetramethyl uronium hexafluorophosphate (0.190 g, 0.50 mmol, HATU), 4-(3-cyclobutylureido)benzoic acid (0.117 g, 0.50 mmol) and N-ethyl-N-isopropylpropan-2-amine (0.13 mL, 0.75 mmol). The reaction mixture was stirred at room temperature for 20 hours and concentrated under vacuum. The residue was diluted with dichloromethane (15 mL) and washed with saturated ammonium chloride (aqueous) and brine. The organic layer was dried (sodium sulfate), filtered and concentrated under vacuum. The crude material was purified by column chromatography on silica (using a solvent gradient of dichloromethane/methanol) to afford the title compound (0.145 g) as a white solid.
