A mixture of 3-phenylpropionic acid (35 mg, 0.23 mmol), (±)-3-amino-5,7-dihydrospiro[cyclopenta[b]pyridine-6,3′-pyrrolo[2,3-b]pyridin]-2′(1′H)-one (71 mg, 0.28 mmol, described in Intermediate 4), N,N,N′,N′-bis(tetramethylene)chloroformamidinium hexafluorophosphate (153 mg, 0.46 mmol), and N,N-diisopropylethylamine (0.20 mL, 1.15 mmol) in THF (2 mL) is stirred at ambient temperature for 18 h. The reaction mixture is purified directly by HPLC using a reversed phase C18 column and eluting with a gradient of H2O:CH3CN:CF3CO2H—90:10:0.1 to 5:95:0.1. The pure, product-containing fractions are combined and made basic with saturated aqueous NaHCO3. The resulting mixture is extracted with EtOAc (3×20 mL), and the combined organic extracts are washed with brine, dried over Na2SO4, filtered, and concentrated in vacuo to provide the title compound.
