Peptide synthesis

Peptide Synthesis

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General scheme of peptide coupling.

Peptide synthesis is the process of creating peptides, which are short chains of amino acids linked by peptide bonds. This process is fundamental in the field of biochemistry and molecular biology, as peptides play crucial roles in biological functions and are used in research and therapeutic applications.

Methods of Peptide Synthesis

Peptide synthesis can be performed using various methods, each with its own advantages and limitations. The two primary methods are liquid-phase peptide synthesis and solid-phase peptide synthesis.

Liquid-Phase Peptide Synthesis

Liquid-phase peptide synthesis involves the sequential addition of amino acids in solution. This method was historically significant but has largely been replaced by solid-phase techniques due to the latter's efficiency and ease of purification.

Solid-Phase Peptide Synthesis

Solid-phase peptide synthesis apparatus.

Solid-phase peptide synthesis (SPPS) is the most common method used today. It involves anchoring the C-terminal amino acid of the peptide to an insoluble resin, allowing for the sequential addition of protected amino acids. This method was pioneered by Robert Bruce Merrifield, who was awarded the Nobel Prize in Chemistry in 1984 for this innovation.

Coupling Reagents

The formation of peptide bonds requires activation of the carboxyl group of the incoming amino acid. Various coupling reagents are used to facilitate this process.

Carbodiimide Reagents

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DIC/HOBt coupling mechanism.

Carbodiimides, such as dicyclohexylcarbodiimide (DCC) and diisopropylcarbodiimide (DIC), are commonly used in peptide synthesis. They activate the carboxyl group to form an active ester, which then reacts with the amine group of the next amino acid.

Additives

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Structure of HOBt.

Additives such as 1-hydroxybenzotriazole (HOBt) and 1-hydroxy-7-azabenzotriazole (HOAt) are often used to suppress racemization and improve yields.

Structure of HOAt.

Protecting Groups

Protecting groups are essential in peptide synthesis to prevent unwanted side reactions. The most common protecting groups are used for the N-terminus and side chains of amino acids.

N-Terminus Protecting Groups

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Cbz protecting group for N-terminus.

The carbobenzyloxy (Cbz), tert-butyloxycarbonyl (Boc), and 9-fluorenylmethyloxycarbonyl (Fmoc) groups are commonly used to protect the N-terminus of amino acids.

Side Chain Protecting Groups

Side chain protecting groups are used to protect functional groups on the amino acid side chains that might react during peptide synthesis.

Deprotection

After the peptide chain is assembled, the protecting groups must be removed to yield the final peptide.

Boc Deprotection

Boc deprotection mechanism.

Boc groups are removed using strong acids such as trifluoroacetic acid (TFA).

Fmoc Deprotection

Fmoc deprotection mechanism.

Fmoc groups are removed using mild bases such as piperidine.

Related Pages

• Amino acid synthesis
• Protein biosynthesis
• Biochemistry