NEW MATERIAL:A compound expressed by formula I [R1 is phenyl or (substituted) lower alkyl;R2 and R3 are H or (substituted) lower alkyl;R4 is H or lower alkyl].

EXAMPLE: N-(N'-Benzylcarbamoyl)phenylalanine methyl ester.

USE: A raw material for producing α-amino acid derivatives useful as food additives or medicines.

PREPARATION: A novel N-carbamoyldehydroamino acid derivative, expressed by formula II and obtained by dehydration condensation of an urea derivative expressed by formula III with an α-ketocarboxylic acid derivative expressed by formula IV is hydrogenated with H2 in the presence of a hydrogenation catalyst, such as rhodium cationic complex expressed by formula V {BPPM is 4(diphenylphosphino)-2-[(diphenylphosphino)methyl]pyrrolidine; COD is 1,5- cyclooctadiene}, in an organic solvent, such as ethanol, under ordinary pressure-150atm hydrogen pressure to readily afford the aimed compound expressed by formula I.