Show all steps necessary to make the dipeptide Phe-Ala

Step 1 of 2

This exercise asks us to show all the steps necessary to make the dipeptide Phe-Ala starting from L-phenylalanine and L-alanine. Recall that by convention, when writing peptide sequences the N-terminus is on the left and the C- terminus is on the right.

We know the N,N’ -dicyclohexylcarbodiimide (DCC) can be used as a coupling agent between an amine group and a carboxyl group. However, ?rst we have to use protecting group chemistry to make sure that the correct amine and carboxyl groups are connected.

Starting with L-phenylalanine, we can protect the N-terminus by treating the amino acid with di-tert-butyl-dicarbonate. Recall that the carbonyl carbons of this reagent are electrophilic, and can be attacked by the nucleophilic amine group of phenylalanine. Reformation of the carbonyl group (with subsequent loss of a leaving group) leaves us with the “protected” form of phenylalanine, where the amino group has a Boc group attached. This will protect the amino terminus of phenylalanine ?om reacting in the DCC coupling step.