Method for producing aspartame derivative, method for purifying the same, crystals thereof and uses of the same

N-[N-[3-(3-methoxy-4-hydroxyphenyl)propyl]-L--aspartyl]-L-phenylalanine 1-methyl ester is prepared by a process comprising:

• subjecting Aspartame and 3-(3-methoxy-4-hydroxyphenyl)propionaldehyde or derivatives thereof to reductive alkylation in a solvent to produce N-[N-[3-(3-methoxy-4-hydroxyphenyl)propyl]-L--aspartyl]-L-phenylalanine 1-methyl ester; and
• crystallizing said compound.