What is solid-phase peptide synthesis?
Solid-phase peptide synthesis builds a peptide chain while it is anchored to an insoluble resin bead. Amino acids are added one at a time from the end of the chain, and because the growing peptide stays fixed to the support, excess reagents and by-products can be washed away between steps.
The approach is repetitive and well suited to automation, which is why it is the standard route for the peptides used in research.
What happens in each synthesis cycle?
Each amino acid is added through a short, repeated cycle. The same sequence runs once per residue until the chain is complete.
| Step | What happens |
|---|---|
| Deprotection | A protecting group is removed to expose the reactive end of the chain |
| Coupling | The next amino acid is activated and joined to the chain |
| Washing | Excess reagents and by-products are rinsed from the resin |
| Repeat | The cycle runs again for the next residue |
| Cleavage | The completed chain is released from the resin and side-chain groups removed |
One residue is added per cycle; the cycle repeats for the length of the chain.
How is the crude peptide purified?
No synthesis is perfect: every coupling step has a yield below 100%, so the crude material that comes off the resin contains the target peptide together with truncated chains and other related impurities.
Preparative HPLC separates the target from those impurities by passing the crude mixture through a column and collecting the target fraction. The purified material is then freeze-dried to a lyophilized powder.
How does synthesis quality affect final purity?
The cleaner the synthesis and the more effective the purification, the higher the purity of the final material and the fewer related impurities remain. But synthesis and purification are claims until they are measured.
That is the role of the Certificate of Analysis: analytical HPLC quantifies the purity of the finished, purified material and mass spectrometry confirms its identity — turning the process into a documented result for a specific batch.