To a solution of 5.30 g (8.0 mmols) of N-benzyloxycarbonyl-β-benzyl-L-aspartyl-O-benzyl-D-threonine (S)-α-ethylbenzylamide in 150 ml of methanol were added 1.0 ml of acetic acid and 3.0 g of 5% Pd-carbon (water content 50%), and the mixture was reduced under hydrogen overnight at room temperature and then at 50° C. for 3 hours. The catalyst was removed by filtration, the resulting filtrate was concentrated under reduced pressure, and the residue was crystallized from water to obtain 1.60 g (4.6 mmols) of α-L-aspartyl-D-threonine (S)-α-ethylbenzylamide.
