2.4- Dinitrofluorobenzene , sequencing peptides with

Chemical methods for determining the amino acid sequence of a peptide or protein have been developed, and the normal approach is to exploit the properties of the amino group at the Al-terminus. A long-established procedure for identifying the N-terminal amino acid is use of the Sanger reagent 2,4-dinitrofluorobenzene. This reacts with an amine by nucleophilic displacement of the fluorine. 

At this point, you can deduce two possible sequences for Q.) (5) Trypsin hydrolysis of L gives a peptide of composition Ala, Asp, Phe which, with 2,4-dinitrofluorobenzene, gives the 2,4-dinitrophenyl derivative of aspartic acid. (6) Partial acid hydrolysis of eledoisin gives several dipeptides, among them Ser-Lys and Pro-Ser. 

The covalent structure of insulin was established by Frederick Sanger in 1953 after a 10-year effort. This was the first protein sequence determination. Sanger used partial hydrolysis of peptide chains whose amino groups had been labeled by reaction with 2,4-dinitrofluorobenzene to form shorter end-labeled fragments. These were analyzed for their amino acid composition and labeled and hydrolyzed again as necessary. Many peptides had to be analyzed to deduce the sequence of the 21-residue and 30-residue chains that are joined by disulfide linkages in insulin. ... 

Dinitrophenylamino acids (DNP-amino acids) and phenylthio-hydantoins (PTH-amino acids) are formed when proteins or peptides are treated with dinitrofluorobenzene [151—154] or phenyl isothiocyanate [155], respectively, and the reaction product suitably broken down. Their separation from the reaction mixture and their identification is of considerable practical importance since systematic application enables sequence analysis of peptide structures to be performed. Numerous investigators have worked on this problem... 

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