PURPOSE: To provide a new amino protective group which is stable to nucleophilic conditions and is adequate for protecting an amino group to allow the operation of a desired functional group in the remaining parts of molecules.

CONSTITUTION: The protective amine of formula II is obtd. by bringing the compd. formula I (Q, Q' are each H, 1 to 6C alkyl or together form -CH= CH-CH=CH-; and R* is an org. residue) and the amine of the formula, HNRR0 (R, R0 are each 1 to 6C alkyl or form an N-contg. ring which may be substd. with one or more 1 to 6C alkyl and/or 1 to 6C substd. alkyl together with the N bonded thereto) into reaction. This protective amine is subjected to nucleophilic reaction and is then treated with an acid, by which the original imide group may be reformed. If the R* residue contains at least one of asymmetrical center, a diastereomer mixture is obtd. by using the amine of the formula, HNRR0 existing in an optically pure form. This diastereomer may be separated by a known method.