An Alloc amino acid is an amino acid in which the amino group is protected by an Alloc group. These amino acids are used in peptide synthesis as orthogonally protected residues, the Alloc group can be removed under conditions different from those used for other protecting groups such as Fmoc or Boc. This allows selective deprotection of specific amino groups during synthesis. They are particularly useful for selective labeling, cyclization, and branch formation in complex peptide synthesis.