To a solution of Boc-Asp(OMe)-OH (5 g, 20 mmol) in acetonitrile (100 mL) was added N-hydroxysuccinimide (2.53 g, 22 mmol) and N,N-dicyclohexylcarbodiimide (4.5 g, 22 mmol). The reaction was stirred at ambient temperature for 4 h. The reaction mixture was filtered directly into an aqueous solution (100 mL) of gabapentin (3.77 g, 22 mmol) and sodium hydrogencarbonate (1.85 g, 22 mmol) and the resulting mixture stirred at ambient temperature for 16 h. The reaction was concentrated under reduced pressure, the residue dissolved in ethyl acetate/diethyl ether (1:1, 300 mL) and washed with 0.1M aqueous potassium hydrogensulfate (2×500 mL). The organic phase was separated, dried over Na2SO4, filtered, and concentrated to dryness under reduced pressure to afford Boc-Asp(OMe)-Gabapentin as a white solid (7.8 g, 19.5 mmol, 98%).
