The general procedure for the synthesis of 2-((4-methoxybenzyl)amino)acetic acid from p-methoxybenzaldehyde and glycine is as follows: note that hydrogen gas is a by-product, and it is necessary to ensure that there is no open flame during the experiment. First, glycine (15.0 g, 0.2 mol) was dissolved in aqueous NaOH (8.0 g, 0.2 mol, 200 mL), followed by the addition of p-methoxybenzaldehyde (27.5 g, 0.2 mol) and ethanol (75 mL). The reaction mixture was stirred continuously using a hot plate magnetic stirrer. The reaction mixture formed a clarified yellow solution within a few minutes, which was subsequently heated to 60 °C and stirring was continued for 2 h without heating. The solution was cooled to 10°C in an ice bath, maintained at this temperature, and NaBH4 (2.50 g, 0.06 mol) was added in batches for 30 minutes. Stirring was continued for 30 minutes without cooling, followed by the addition of a second portion of p-methoxybenzaldehyde (13.6 g, 0.1 mol). After cooling to 10 °C, NaBH4 (1.25 g, 0.03 mol) was added in portions over 15 min and stirring was continued for 30 min. The reaction mixture was again cooled to 10 °C and a third portion of p-methoxybenzaldehyde (13.6 g, 0.1 mol) and NaBH4 (1.50 g, 0.04 mol) was added as previously described. The reaction mixture was placed in a refrigerator (~5°C) overnight. On the following day, the solution was concentrated to 200 ml in a fume hood to remove ethanol, cooled, and extracted with chloroform (100 ml for the first time and 50 ml for each of the next two times). The upper aqueous phase was acidified with dilute hydrochloric acid (60 mL; 1:1, v/v) to pH ≈ 6.5 and allowed to stand for 2 hours. The precipitated white solid was collected by filtration and the filtrate was concentrated to 100 mL, where the product began to crystallize. After cooling in an ice bath, the product was collected by diafiltration and washed quickly with ice water (40 mL). Yield: 13.2 g (33%).
