A dipeptide, “x”, on complete hydrolysis gives “y” and “z”; “y” on treatment with aqueous HNO$_2$, produces lactic acid. On the other hand, “z” on heating gives the following cyclic molecule.
Based on the information given, the dipeptide X is:
A dipeptide, “x”, on complete hydrolysis gives “y” and “z”; “y” on treatment with aqueous HNO$_2$, produces lactic acid. On the other hand, “z” on heating gives the following cyclic molecule.
Based on the information given, the dipeptide X is:
Show Hint
- valine-glycine
- alanine-glycine
- valine-leucine
- alanine-alanine
The Correct Option is B
Approach Solution - 1
To determine the dipeptide "x," we need to analyze the amino acids "y" and "z" obtained upon its hydrolysis:
- Information about "y": The amino acid "y" on treatment with aqueous HNO2 produces lactic acid. This transformation suggests that "y" is likely to be alanine. The reaction of alanine with HNO2 results in the formation of lactic acid through the loss of the amino group and subsequent rearrangement.
- Information about "z": The amino acid "z," upon heating, forms the given cyclic molecule. The structure presented corresponds to a diketopiperazine formed by condensation of glycine. Such a cyclization is characteristic of glycine.
- Identifying the Dipeptide:
- Since "y" is alanine and "z" is glycine, the dipeptide "x" must be alanine-glycine.
Hence, based on the transformations and information given, the dipeptide "x" is identified as alanine-glycine.
Approach Solution -2
Let’s break down the key information provided:
1. Hydrolysis of “x”:
- The dipeptide "x" undergoes complete hydrolysis to produce two amino acids: y and z.
- y is a compound that, when treated with aqueous HNO\(_2\), produces lactic acid. This strongly suggests that y is glycine, as glycine reacts with nitrous acid to form lactic acid.
Therefore, glycine must be one of the products after hydrolysis.
2. Heating of “z”:
- z on heating forms a cyclic molecule. This strongly indicates that z is proline, as proline is an amino acid that can form a cyclic structure under heating conditions.
3. Identifying the Dipeptide:
- The dipeptide must be one that hydrolyzes to give glycine (which produces lactic acid upon treatment with HNO\(_2\)) and proline (which forms a cyclic structure upon heating).
- The only dipeptide in the given options that fits this pattern is alanine-glycine (option 2), as alanine can undergo cyclization to form proline under heat.
Thus, the correct dipeptide x is alanine-glycine.
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