Solid-phase peptide synthesis, usually abbreviated SPPS, builds a peptide while the growing chain is covalently attached to a solid support. The defining feature is that attachment. Reagents and solvents still take part in the chemistry, so solid-phase does not mean that a dry peptide is assembled without a liquid environment.
Understand what the support holds
Merrifield's 1963 paper demonstrated stepwise addition of protected amino acids to a chain attached to resin. The chain remained bound during assembly and was released afterwards. This made the physical handling of successive reactions different from repeatedly isolating a freely dissolved peptide intermediate.Merrifield — Solid Phase Peptide Synthesis I (opens in a new tab)
The term resin refers to the support material, not an ingredient intended to remain covalently attached to the finished free peptide. The connecting chemistry has to be considered separately because the point at which the product is released helps define the resulting molecular end groups.
| Object | Role |
|---|---|
| Solid support | Retains attached material during assembly |
| Linker or anchoring connection | Joins the growing chain to the support |
| Growing peptide | The changing molecular sequence |
| Released product | Material requiring its own identity and composition assessment |
Read the repeating cycle as controlled exposure
At a conceptual level, temporary protection controls which group can react. Removing the relevant protection exposes the next attachment site, and coupling adds a building block. Repeating those operations extends the sequence. Merrifield's lecture explains this general scheme and its handling advantages.Bruce Merrifield — Nobel Lecture (opens in a new tab)
Conventional linear SPPS commonly anchors the future C-terminal residue and extends the chain towards its N-terminus. The written sequence is still read from N to C. Reading direction and assembly direction therefore should not be confused.Merrifield — Solid Phase Peptide Synthesis I (opens in a new tab)
For a schematic target Ala-Gly-Ser, Ser can be the support-bound starting residue, then Gly and Ala are added in that order. The final sequence is written Ala-Gly-Ser, not Ser-Gly-Ala. This is an orientation illustration, not an operational synthesis procedure.
An attached chain can carry an error forward
Consider an invented assembly in which one intended addition fails on a small subset of chains, but a later addition succeeds on those same chains. The physical fact that they remained attached does not correct the earlier omission. Washing removes soluble material; it does not inherently rewrite an incorrect attached sequence.
A simple probability model illustrates accumulation. If ten required events each have an independent 99% probability of being correct, the probability that all ten are correct is 0.99 to the power ten, about 90.4%. This is not a measured coupling efficiency or a prediction of crude peptide purity.
Read a synthesis method separately from a test result
A statement that a peptide was made by SPPS identifies an assembly approach. It does not provide the final sequence confirmation, counterion composition, content measurement or impurity profile. Those belong to characterisation of the recovered material.
Likewise, reporting that the synthesiser completed its programmed cycles is a process record. It is not equivalent to demonstrating that every recovered molecule matches the intended structure. Keep the programmed target, intermediate observations and final analytical results as separate evidence.
- Locate the support and anchoring connection.
- Read the final sequence independently of assembly direction.
- Do not treat washing as sequence-specific purification.
- Use final characterisation to assess the recovered material.
Sources and further detail
- Merrifield — Solid Phase Peptide Synthesis I (opens in a new tab)
JACS 85, 2149–2154 (1963). Original resin-bound tetrapeptide synthesis; historical chemistry is not a description of a current supplier's process.
- Bruce Merrifield — Nobel Lecture (opens in a new tab)
Inventor's account of the solid-phase assembly principle. Conceptual passages used; no production recipe or universal yield is inferred.
Sources checked 19 September 2026. Worked examples are illustrative unless a supplied report is explicitly identified. This article has not undergone independent scientific peer review.