2,4-Dinitrofl uorobenzene, very often known as Sangers

Chapter 27, Problem 27.5

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2,4-Dinitrofl uorobenzene, very often known as Sangers 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 for chemistry for his work in determining the primary structure of bovine insulin. One of the few persons 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. F 1 O O H2NCHCNHCHC9polypeptide NO2 2,4-Dinitrofluorobenzene (N-Terminal end of a polypeptide chain) polypeptide chain in which the N-terminal amino acid is labeled with a 2,4-dinitrophenyl group O2N R1 R2 Following reaction with 2,4-dinitrofl uorobenzene, 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 identifi ed. (a) Write a structural formula for the product formed by treatment of the N -terminal amino group with Sangers reagent and propose a mechanism for its formation. (b) When bovine insulin is treated with Sangers 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 Sangers reagent with that from use of the Edman degradation.