Illustrated Glossary of Organic Chemistry

Sanger's reagent: 1-Fluoro-2,4-dinitrobenzene. Undergoes nucleophilic aromatic substitution 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).

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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.




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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.