Number of Distinct Naturally Occurring Amino Acids from Peptide Hydrolysis

To determine the total number of distinct naturally occurring amino acids produced upon complete acidic hydrolysis of the given peptide structure, we analyze the cleavage of all amide (peptide) bonds in the molecule.

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Step 1: Cleavage of Amide Bonds

Upon complete acidic hydrolysis, every amide bond ($-\text{C}(=\text{O})-\text{N}-$) is cleaved to yield the corresponding carboxylic acid ($-\text{COOH}$) and amine ($-\text{NH}_3^+$) groups.

Analyzing the peptide chain from left to right:

1. Left Terminal Diketopiperazine Ring:

   • The six-membered cyclic ring contains two amide bonds with the formula unit corresponding to two glycine residues linked head-to-tail: $\text{Cyclo}(\text{Gly-Gly})$
   • Hydrolysis of this ring breaks both amide bonds to produce 2 molecules of Glycine: $\text{H}_2\text{N}-\text{CH}_2-\text{COOH}$

2. Residue with Cyclopropyl Side Chain:

   • Hydrolysis of the adjacent peptide bonds yields 2-amino-3-cyclopropylpropanoic acid: $\text{H}_2\text{N}-\text{CH}\left(\text{CH}_2-\text{C}_3\text{H}_5\right)-\text{COOH}$

3. Residues with $tert$-Butyl Side Chains:

   • Hydrolysis of the central residues yields 2-amino-3,3-dimethylbutanoic acid ($tert$-leucine): $\text{H}_2\text{N}-\text{CH}\left(\text{C}(\text{CH}_3)_3\right)-\text{COOH}$

4. Right Terminal Diketopiperazine Ring:

   • Similar to the left ring, hydrolysis of this cyclic structure yields 2 more molecules of Glycine: $\text{H}_2\text{N}-\text{CH}_2-\text{COOH}$

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Step 2: Evaluation of Natural Occurrence

Now, we evaluate the resulting distinct amino acids for natural occurrence (i.e., standard proteinogenic amino acids):

1. Glycine ($\text{H}_2\text{N}-\text{CH}_2-\text{COOH}$):

   • This is the simplest standard proteinogenic amino acid and is naturally occurring.

2. 2-amino-3-cyclopropylpropanoic acid:

   • This compound contains a cyclopropyl ring and is not one of the standard naturally occurring amino acids.

3. 2-amino-3,3-dimethylbutanoic acid ($tert$-leucine):

   • This compound contains a $tert$-butyl side chain and is not a naturally occurring amino acid.

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Conclusion

The only distinct naturally occurring amino acid produced upon complete acidic hydrolysis is Glycine.

Thus, the total count of distinct naturally occurring amino acids obtained is 1.