Illustrated Glossary of Organic Chemistry

Sanger's reagent: 1-Fluoro-2,4-dinitrobenzene. Undergoes nucleophilic aromatic substitution (NAS) with the N-terminal amino group of a peptide or protein, resulting in a chemical tag on the terminal amino acid residue. After hydrolysis into individual amino acids, the peptide's or protein's terminal amino acid can be identified by the specific wavelength of light absorbed (i.e., colorimetric analysis).

	+		NAS
Sanger's reagent		Gly-Ala-Ser		Labeled tripeptide

The N-terminal amino group of the tripeptide Gly-Ala-Ser replaces the fluoride of Sanger's reagent via a nucleophilic aromatic substitution mechanism.

	Hydrolysis		+		+
Labeled tripeptide		Glycine Labeled		Alanine Not labeled		Serine Not labeled

Hydrolysis of the labeled tripeptide gives three amino acids. Glycine bears the tag, so glycine was the N-terminal amino acid residue in the starting tripeptide.