2,4-Dinitrofluorobenzene, very often known as Sanger's reagent after the English chemist Frederick Sanger who popularized its use, reacts selectively with the N-terminal amino group of a polypeptide chain. Sanger was awarded the 1958 Nobel Prize in Chemistry for his work in determining the primary structure of bovine insulin. One of the few people to be awarded two Nobel prizes, he also shared the 1980 award in chemistry with American chemists Paul Berg and Walter Gilbert for the development of chemical and biological analyses of DNA.
Following reaction with 2,4-dinitrofluorobenzene, all amide bonds of the polypeptide chain are hydrolyzed and the amino acid labeled with a 2,4-dinitrophenyl group is separated by either paper or column chromatography and identified.
(a) Write a structural formula for the product formed by treatment of the N-terminal amino group with Sanger's reagent and propose a mechanism for its formation.
(b) When bovine insulin is treated with Sanger's reagent followed by hydrolysis of all peptide bonds, two labeled amino acids are detected: glycine and phenylalanine. What conclusions can be drawn from this information about the primary structure of bovine insulin?
(c) Compare and contrast the structural information that can be obtained from use of Sanger's reagent with that from use of Edman degradation.
