71989-14-5

144120-52-5

71989-14-5

The general procedure for the synthesis of Fmoc-L-aspartic acid β-tert-butyl ester from the compound (CAS:144120-52-5) was as follows: firstly, PdEnCat 30 (Aldrich; loading 0.4 mmol/g, use 0.05 eq.) was suspended in THF-H2O (9:1 v/v, total 5 mL) and treated with argon bubbling for 10 min for deoxygenation. Subsequently, DCHT (0.15 eq.) and the corresponding ester 1 (1.0 eq., 70 mg) were added under positive pressure. Finally, PhSiH3 (2.0 eq.) was injected and the reaction mixture was allowed to react at room temperature for 2 h. The reaction was carried out under low pressure. After completion of the reaction, the mixture was filtered through Celite and the filtrate was concentrated under reduced pressure. The residual solid was dissolved with EtOAc (20 mL) and washed sequentially with H2O (3 x 10 mL) and brine (3 x 10 mL). The organic layer was dried over MgSO4 and concentrated in vacuum. Purification was carried out by solid phase extraction (using C18 reversed-phase chromatography with H2O/MeOH as eluent) to obtain pure carboxylic acid 2 (see Table 1 for yields). The purity of the products was confirmed analytically by HPLC, 1H NMR and 13C NMR. All the carboxylic acids were commercially available. The 1H and 13C NMR spectra of the synthesized compounds were in agreement with those of commercial samples.