General procedure for the synthesis of L-ornithine L-aspartate salt from L-aspartate and L-ornithine acetate: 22.5 g of L-ornithine acetate (monohydrate) and 13.3 g of L-aspartate were added to 20 mL of purified water and mixed with stirring. Ammonium carbonate solution (prepared by dissolving 9.9 g of ammonium carbonate in 40 mL of pure water) was slowly added dropwise, with the rate of acceleration of the droplets being controlled in response to the accompanying slight exothermic and CO2 gas release. After observing that the suspension gradually became clarified, stirring was continued for 10 min to ensure that the pH of the reaction solution was maintained at 7.0-8.0. Subsequently, the reaction solution was heated to 70-80 °C, and 150 mL of methanol was slowly added to induce precipitation of solids. The crystallization process was continued for 2 hours, then slowly cooled to room temperature and stirring was continued for 2 hours. The solid was collected by filtration and washed once with a mixture of methanol and water (4:1 v/v, about 50 mL), then with pure methanol (50 mL x 2). After the above treatment, 21.7 g of wet solid product was obtained, which did not need to be dried and was directly used in the next step of refinement. Dissolve 21.7 g of aspartic ornithine wet crude product in 42 mL of pure water and stir until completely dissolved. It was heated to 60-70°C, and about 0.6 g of activated carbon was added and thermally decolorized for 30 minutes. After filtration, the filtrate was reheated to 70-80°C and about 84 mL of methanol was added slowly to induce precipitation of solids. After dropwise addition, stirring was continued for 2 hours, then slowly cooled to room temperature and stirred for another 2 hours. The solid was collected by filtration and washed sequentially with a mixture of methanol and water (4:1, 50 mL x 2, by volume) and pure methanol (50 mL x 2). Finally, 18.3 g of pure product was obtained by drying under reduced pressure with a specific rotation of +28.1° and a purity of 99.56%.
