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ChemistryInteger+3Question 36 of 60

JEE Advanced 2014 · Paper 1, Chemistry question 36

The total number of distinct naturally occurring amino acids obtained by complete acidic hydrolysis of the peptide shown below is

A linear peptide capped at both ends by N-substituted 2,5-diketopiperazine rings (glycine anhydride). The chain, left to right: DKP N-CO-CH(CH₂-cyclopropyl)-NH-CO-CH(tBu)-NH-CO-CH(tBu)-NH-CO-CH(tBu)-NH-CO-CH(CH₂-cyclopropyl)-N of the second DKP ring.
Answer and worked solution

Official answer: 1

Hydrolysis products.

  • The two 2,5-diketopiperazine end rings are cyclic glycine dipeptides; they give glycine.
  • The residues with a CHX2\ce{CH2}-cyclopropyl side chain give β-cyclopropylalanine, which is not one of the naturally occurring (protein) amino acids.
  • The residues with a tert-butyl side chain give tert-leucine, also not naturally occurring.

Only one distinct natural amino acid, glycine, is obtained.

Answer: 1

Topics:Amino acids and proteins
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