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Chapter 21: Q40P (page 1018)

Explain why cyanogens bromide does not cleave on the C-side of cysteine.

Short Answer

Expert verified

The answer is

Imine is not formed due to the difficulty in the formation of the strained four-membered ring.

Step by step solution

01

Step-by-Step Solution Step 1: Cysteine

The amino acids are the simple basic units of peptides and proteins. Cysteine is an amino acid containing a sulfur atom.

02

Explanations

The structure of cysteine is given below.

Cysteine can react with cyanogens bromide, and the sulfur will not be positively charged, hence a poor leaving group. In addition, the lactone will not be formed as it would have a strained four-membered ring. The imine will not be formed without lactone formation, and therefore, the cleavage cannot occur.

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Most popular questions from this chapter

alpha- Amino acids can be prepared by treating an aldehyde with ammonia/trace acid, followed by hydrogen cyanide, followed by acid-catalyzed hydrolysis.

a. Draw the structures of the two intermediates formed in this reaction.

b. What amino acid is formed when the aldehyde that is used is 3-methylbutanal?

c. What aldehyde is needed to prepare isoleucine?

Show the steps in the synthesis of the tetrapeptide in problem 34, using Merrifield’s method.

Explain the difference in the \({\bf{p}}{{\bf{K}}_{\bf{a}}}\) values of the carboxyl groups of alanine, serine, and cysteine.

Treatment of a polypeptide with 2-mercaptoethanol yields two polypeptides with the following primary structures:

Val-Met-Tyr-Ala-Cys-Ser-Phe-Ala-Glu-Ser

Ser-Cys-Phe-Lys-Cys-Trp-Lys-Tyr-Cys-Phe-Arg-Cys-Ser

Treatment of the original intact polypeptide with chymotrypsin yields the following peptides:

1. Ala, Glu, Ser 3. Tyr, Val, Met 5. Ser, Phe, 2 Cys, Lys, Ala, Trp

2. 2 Phe, 2 Cys, Ser 4. Arg, Ser, Cys 6. Tyr, Lys

Determine the positions of the disulfide bridges in the original polypeptide.

What amino acid is formed using the N-phthalimidomalonic ester synthesis when the following alkyl halides are used in the third step?

(a)

(b) CH3SCH2CH2Br
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