Devise a synthesis of each peptide from amino acid starting materials: (a) Leu–Val; (b) Ala–Ile–Gly.

The amino acids, Leucine and Valine, exist as shown:

The structure of Leu-Val dipeptide is:

The synthesis of Leu-Val dipeptide involves the following steps:

• Protect the amine group in Leucine by reacting with Boc.
• Protect the carboxylic acid group in -Val as a benzyl ester.
• Then both are allowed to react to form the required dipeptide in the presence of DCC.
• In the last step, the protecting groups should be removed.

Protecting Groups

Synthesis of Leu-Val

The amine group is protected with Boc(t-butyloxycarbonyl) group, and the carboxylic acid group is protected with benzyl alcohol in the presence of mild acid.

• First, in Ala, the amine group is protected with Boc.
• Next, the –COOH group in Ile amino acid is protected with benzyl alcohol.
• Next, these two amino acids are allowed to react with each other then an amide group is formed, a dipeptide of Ala-Ile with protecting groups.
• The carboxylic acid group in glycine is protected. This amino acid is allowed to react with the dipeptide.

Thus, the required tripeptide will be obtained.