Peptide Synthesis - Protecting Groups - N-terminal Protecting Groups

N-terminal Protecting Groups

Amino acids are added to excess to ensure complete coupling during each synthesis step, and without N-terminal protection, polymerization of unprotected amino acids could occur, resulting in low peptide yield or synthesis failure. N-terminal protection requires an additional step of removing the protecting group, termed deprotection, prior to the coupling step, creating a repeating design flow as follows:

• Protecting group is removed from the trailing amino acids in a deprotection reaction
• Deprotection reagents are washed away to provide a clean coupling environment
• Protected amino acids dissolved in a solvent such as dimethylformamide (DMF) combined with coupling reagents are pumped through the synthesis column
• Coupling reagents are washed away to provide clean deprotection environment

Currently, two protecting groups (t-Boc, Fmoc) are commonly used in solid-phase peptide synthesis. Their lability is caused by the carbamate group which readily releases CO₂ for an irreversible decoupling step.