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JEE Main · 2025 · 04 Apr 2025 · Shift 2 · Biomolecules

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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✓ Correct
  3. (C)valine-leucine
  4. (D)alanine-alanine

Answer: (B)

Solution

Complete hydrolysis splits the dipeptide into two amino acids. The one that reacts with nitrous acid to give lactic acid, , must have begun as the matching -amino acid , which is alanine, since nitrous acid replaces the amino group by a hydroxyl. The other residue, on heating, forms the symmetric six-membered diketopiperazine carrying two groups and two units, which is the cyclic anhydride of glycine, so that residue is glycine. The dipeptide is therefore alanineglycine.

JEE Main · 2025 · 04 Apr 2025 · Shift 2 · Single correct option

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