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JEE Main 2025 Apr 4 Shift 2, Chemistry Q4: Proteins

JEE Main2025Apr 4, Shift 2Chemistry
Q.

A dipeptide, "x" on complete hydrolysis gives "y" and "z". "y" on treatment with aq. produces lactic acid. On the other hand "z" on heating gives the following cyclic molecule.

Based on the information given, the dipeptide X is:

  1. A

    valine-glycine

  2. B

    alanine-glycine

  3. C

    valine-leucine

  4. D

    alanine-alanine

Solution

Two clues fix the two amino acids.

Identifying y:
Aqueous converts a primary -amino group into an -hydroxyl group (). Since the product is lactic acid, , the parent amino acid must be alanine, .

.

Identifying z:
The cyclic product on heating is a six-membered 2,5-diketopiperazine with two unsubstituted groups between the two amide nitrogens. Only glycine () gives this symmetrical diketopiperazine on self-condensation.

.

Hence the dipeptide X is alanine-glycine.

Concept behind this question

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