Imino acid

In organic chemistry, an imino acid is any molecule that contains both imine (>C=NH) and carboxyl (-C(=O)-OH) functional groups.

[1] Imino acids are structurally related to amino acids, which have amino group instead of imine—a difference of single vs double-bond between nitrogen and carbon.

Secondary amino acids, amino acids containing a secondary amine group are sometimes named imino acids,[2][3] though this usage is obsolescent.

[1] The only proteinogenic amino acid of this type is proline, although the related non-proteinogenic amino acids hydroxyproline[4][5][6] and pipecolic acid[7] have often been included in studies of this class of compounds.

The term imino acid is also the obsolete term for imidic acids, structures containing the -C(=NH)-OH group, and should not be used for them.