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Chapter 24: Q11P. (page 1270)

  1. Show how you would use a Strecker synthesis to make phenylalanine.
  2. Propose a mechanism for each step in the synthesis in part (a).

Short Answer

Expert verified

(a)

Formation of phenylalanine

(b)

Formation of protonated amine

Addition of CN group

Formation of phenylalanine

Step by step solution

01

Strecker synthesis

A large number of amino acids can be formed from appropriate aldehydes by a process known as Strecker synthesis. In this synthesis, an aldehyde is treated with ammonia NH3and hydrogen cyanide HCN,followed by hydrolysis H3O+.

02

(a)

The Strecker synthesis ofalanine is shown by the reaction shown below:

Formation of phenylalanine

(b)

The mechanism for each step in the synthesis of phenylalanine is shown below:

Addition of CN group

Formation of phenylalanine

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Show the third and fourth steps in the sequencing of oxytocin. Use figure 24-14 as a guide.

Peptides often have functional groups other than free amino groups at the N terminus and other than carboxyl groups at the C terminus.

(a) A tetrapeptide is hydrolyzed by heating with 6 M, and the hydrolysate is found to contain Ala, Phe, Val, and Glu. When the hydrolysate is neutralized, the odor of ammonia is detected. Explain where this ammonia might have been incorporated in the original peptide.

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Draw the electrophoretic separation of Ala, Lys, and Asp at pH 9.7.

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