A 250 mL three-necked flask was loaded consecutively with water (20 mL), 1,4-dioxane (20 mL), and L-lysine (2.1 g, 14.4 mmol). The mixture was stirred until complete dissolution. The pH was adjusted to about 10.5 by the addition of 30% NaOH. Benzyl chloroformate (5.2 g, 30.6 mmol) was added while maintaining the pH at about 1011 by adding at the same time 30% NaOH. At the end of the addition, the reaction was stirred at 20° C. for about 1 hour. The pH was adjusted to 5 with 37% HCl. Ethyl acetate (30 mL) was added and the pH was adjusted to 1 with 37% HCl. The mixture was stirred at room temperature for about 30 minutes, the organic layer was separated and the aqueous layer was extracted with ethyl acetate (20 mL). The combined organic layer was washed with brine (30 mL) and dried over Na2SO4. Then, the solvent was evaporated to yield Z-Lys(Z)-OH as a yellowish oil (6.0 g, 99%).
