To a stirred aqueous solution (400 mL) of DL-homocystine 1 (25.0 g, 93.2 mmol) in 10% sodium carbonate, di-tert-butyl dicarbonate (45.0 g, 207 mmol) in 1,4-dioxane (200 mL) was added dropwise at 0 o C. The mixture was slowly warmed to r.t. and stirred for 5 hours. After the completion of reaction, the solution was acidified to pH 4 by 10% citric acid in water. Then, the resulting mixture extracted with EA (3 × 100 mL) and the organic layer was washed with brine (2 × 100 mL). The organic layer was dried over MgSO4 and concentrated under reduced pressure to give a white powder. The white powder was dissolved in dry DMF (350 mL) and sodium bicarbonate (15.0 g, 179 mmol) was added to the solution. Then, benzyl bromide (40.0 g, 234 mmol) was added to the reaction and the mixture was stirred at r.t. After 5 hours, EA (100 mL) and water (50 mL) were added to the mixture while stirring. The mixture was extracted with EA (3 × 100 mL), and the organic layer was washed with water (5 × 150 mL) and brine (150 mL). The organic layer was dried over MgSO4 and concentrated followed under reduced pressure to obtain a crude product, which was recrystallized in cyclohexane at -20 o C. The white crystal obtained was dissolved in DMF (300 mL)