DMAP (194 mg, 1.58 mmol) and DIC (N,N-diisopropylcarbodiimide) (740 μl, 4.76 mmol) were added to a solution of L-phenylalanine methyl ester hydrochloride (684 mg, 3.17 mmol) and p-tolylacetic acid (500 mg, 3.33 mmol) in dry DCM (35 ml). After 24 h at room temperature the solvent was removed under reduced pressure and the crude residue was purified by flash chromatography (DCM containing 1% EtOH) to afford (S)-methyl 2-[2-(4-methylphenyl)acetamido]-3-phenyl-propanoate in quantitative yield. The product was diluted with methanol (78 ml) and then an aqueous solution of NaOH (1N, 14.2 ml, 14.2 mmol) was added. The reaction mixture was stirred for 1 h at room temperature and concentrated. Then water and HCl 1N was added until pH 2. The organic product was extracted with DCM (3×50 ml), dried with Na2CO3 and concentrated under reduced pressure to afford (S)-2-[2-(4-methylphenyl)acetamido]-3-phenyl-propionic acid as a white solid (94% c.y.)
