General procedure for the synthesis of di-tert-butyl (S)-2-aminosuccinate hydrochloride from Cbz-Asp(OtBu)-OtBu 18: Pd/C (10%, 830 mg, 10% w/w) was added to an ethanol solution of Cbz-Asp(OtBu)-OtBu 18 (8.25 g, 21.8 mmol) and ammonium formate (34.3 g, 0.54 mol). ) in an ethanol solution (20 mL). The suspension was stirred overnight at room temperature. Upon completion of the reaction, the suspension was filtered through diatomaceous earth and the solvent was removed under reduced pressure. The resulting residue was dissolved in ethyl acetate and the solution was cooled to 0°C. Subsequently, an ethyl acetate solution saturated with HCl was added dropwise and stirred for 15 minutes. The precipitated solid was filtered, washed with cold ethyl acetate and dried under vacuum to afford NH2-Asp(OtBu)-OtBu hydrochloride 16 (4.28 g, 17.4 mmol, 80% yield) as a white solid, which can be used in subsequent reactions without further purification.
