Step 5. A mixed solution of L-citrulline (10 g, 68.4 mmol) and basic copper carbonate (15.12 g, 68.4 mmol) in distilled water (100 mL) was heated to reflux for 30 minutes. Solids generated during refluxing were removed by thermal filtration. The filtrate was cooled to 0 °C and the pH was adjusted to 9 by addition of anhydrous sodium carbonate (1.0 g). allyl chloroformate (10.8 mL, 102.6 mmol) was added slowly and dropwise while stirring at 0 °C. During dropwise addition, the pH of the reaction mixture was maintained at 9 by addition of anhydrous sodium carbonate (20 g). the reaction mixture was gradually warmed up to room temperature with continuous stirring for 12 h. The reaction was carried out by filtration. Upon completion of the reaction, the resulting blue solid product was quantitatively collected by filtration. The resulting copper salt solid of Orn (Alloc) was suspended in distilled water (200 mL) and thioacetamide (6.511 g, 86.66 mmol, 2 equiv) was added. The basic suspension was stirred at 50 °C for 3 h, during which time the solid gradually dissolved. Subsequently, the solution was acidified to pH 2 with 2 M hydrochloric acid and boiling was continued for 5 min. The resulting copper sulfide precipitate was removed by filtration. The filtrate was concentrated under reduced pressure to about 100 mL, at which point the hydrochloride product of Orn (Alloc) precipitated quantitatively as a white solid.
