Chapter 27: Amino Acids, Peptides and Proteins

Peptide Synthesis : Protecting groups

• Protein synthesis is important for several reasons including:
• confirming the structure of natural proteins (e.g. for medical research etc.)
• to investigate how protein structure and function are controlled by the amino acid sequence.

• However, it is not as straight forward as mixing the amino acids together to form the amides.
• For example, a mixture of alanine, A and glycine, G would give a mixture of amides : A-G, G-A, A-A and G-G,  plus higher polypeptides...)
• In order to control the coupling reaction, it is necessary to use protecting groups.
• By protecting the amine group of one component and the carboxylic acid group of the other, a specific amide bonds can be formed.

• Therefore the sequence required is to:
• protect the amino group in the N-terminal amino acid and the carboxyl group in the C-terminal amino acid
• couple the two amino acids by forming the new amide bond
• deprotect the termini of the new peptide (as and if required)
• By repeating the process, polypeptides can be grown one amino acid residue at a time, or by building pieces and then joining those together.

 

Amine protecting groups
	1.   benzoyloxycarbonyl groups (abbreviation = Z or Cbz in older literature)
	protection
	deprotection
	2.   tert-butoxycarbonyl groups (abbreviation = Boc)
	protection
	deprotection
Carboxyl protecting groups
	1.   simple esters esp. methyl, and ethyl
	protection
	deprotection
	2.   benzyl esters (abbreviation = Bn)
	deprotection

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