A dipeptide, "x" on complete hydrolysis gives "y" and "z". "y" on treatment with aq. HNO2 produces lactic acid. On the other hand "z" on heating gives the following cyclic molecule. [figure] Based on the information given, the dipeptide "x" is :
- alanine-alanine
- valine-glycine
- valine-leucine
- alanine-glycine
Answer
(4) alanine-glycine
Solution
y + HNO2 (aq) lactic acid, CH3CH(OH)COOH; HNO2 replaces -NH2 by –OH:
CH3CH(NH2)COOH HNO2 CH3CH(OH)COOH + N2 + H2O
y = alanine
z on heating gives the cyclic diamide (2,5-diketopiperazine) in which each ring unit is -NH-CH2-CO-; it is formed from two molecules of H2N-CH2-COOH with loss of two H2O.
z = glycine
x = alanine-glycine
Answer: (4)