Short answer
Custom peptide synthesis is a service that builds a specific amino acid sequence for a researcher, then purifies and tests it. Most peptides are made with solid-phase peptide synthesis (SPPS), which attaches amino acids one by one to a solid resin.
What is solid-phase peptide synthesis?
Solid-phase peptide synthesis (SPPS) is the standard method for making peptides in the laboratory. First described in the 1960s, it attaches the first amino acid to a solid resin bead, then adds the remaining amino acids one at a time. When the chain is complete, the peptide is cleaved from the resin and purified [1].
A 2018 historical review traces thirteen decades of peptide chemistry and explains why SPPS became the dominant approach: the solid support simplifies handling, excess reagents are washed away at each step, and the method scales from milligrams in a research lab to kilograms in an industrial setting [2]. The review also explains the two main protecting-group strategies used in SPPS - the Boc/Bzl approach and the Fmoc/tBu approach - and how each influences coupling efficiency and the choice of cleavage chemistry.
The main steps are:
A recent perspective in the peptide science literature emphasizes that the peptide-resin system itself determines much of SPPS behavior - swelling, solvation and accessibility all change as the chain grows - and that understanding these fundamentals is the key to making synthesis greener and more efficient [3].
Why labs use custom synthesis
Custom synthesis matters when off-the-shelf catalog peptides do not exist, when you need a specific modification for a conjugation or labeling experiment, or when you want full control over purity and documentation. It is also the standard route when a sequence contains amino acids that are difficult to couple or prone to aggregation during chain assembly.
Purity grades explained
| Grade | Typical HPLC purity | Best for |
|---|---|---|
| Crude | 60-80% | Screening and method development |
| Standard | 85-95% | Most cell-based and biochemical assays |
| High purity | 95-98% | Structure-activity studies |
| Research grade | 99%+ | Sensitive assays and analytical work |
Higher purity costs more and takes longer, so choose the grade that matches your experiment rather than always ordering the maximum. A structure-activity study that compares many analogs may tolerate 90% purity, while a quantitative binding assay with a labeled tracer typically warrants 98% or higher. Your experiment design, not habit, should set the grade.
Understanding the impurity picture
No synthetic peptide is perfectly pure. The impurities you should understand fall into a few categories:
A review of peptide impurities explains that many of these arise during synthesis itself or during storage, and that their identity and quantity depend on the specific sequence and the manufacturing controls in place [4]. This is why the COA matters: it tells you which impurities were measured, how much of each is present, and whether the batch meets the purity specification you paid for. The two most relevant impurities for most experiments are truncations and oxidation products, because both can change the apparent activity of the material.
Difficult sequences and how suppliers handle them
Some sequences are harder than others. Runs of hydrophobic residues can cause incomplete couplings; sequences rich in cysteine can oxidize and aggregate; long chains lose synthesis efficiency with each added residue. A good supplier will flag a difficult sequence before quoting, suggest where the problem is likely to be, and adjust the chemistry - different coupling reagents, a longer deprotection step or a different resin loading - to compensate. A supplier that quotes every sequence identically has not thought much about your project.
Modifications and labels, explained
The most common modifications and what they are used for:
Tell the supplier exactly which modification you want and confirm it is supported before you order. An unlisted modification is a red flag for timeline and cost surprises.
Solubility and buffer compatibility
Custom peptides arrive lyophilized and must be reconstituted for laboratory use. Solubility is sequence-dependent: charged and hydrophilic residues dissolve readily in aqueous buffer, while hydrophobic stretches often need a small amount of organic solvent or dilute acid. Ask the supplier for solubility guidance and, if your sequence is difficult, request solubility testing. Reconstitution guidance is part of the deliverable, not a courtesy.
Scales, cost drivers and lead times
The quoted price and lead time depend on the length of the sequence, the purity grade, the scale and the difficulty of the chemistry. Longer chains need more coupling cycles; higher purity needs more aggressive purification and re-analysis; difficult sequences may need multiple attempts. When comparing quotes, make sure the purity grade, the net peptide content and the scale are apples to apples - a cheap quote at 80% purity is not the same product as a careful quote at 98% purity.
Documents you should receive
Every custom synthesis order should end with a small documentation set: a COA with the HPLC chromatogram and mass spectrum, the sequence file, the batch number and the storage conditions. Keep these together. If your institution requires purchase documentation or material safety data, ask for those as well. The COA is the scientific record; the rest is the administrative record. You want both.
What to ask a synthesis supplier
Scaling up and reproducibility
If your project will move from a single assay to a larger study, ask about batch-to-batch reproducibility. A good supplier can produce the same sequence at different scales and confirm that the analytical profile - retention time, mass, purity, impurity pattern - is consistent across batches. Reproducibility is often more valuable than a marginally higher purity number, because it means your results can be repeated by another researcher using a second batch.
Confirm your sequence before ordering
Before you submit, check the sequence one last time - the reading frame, the termini and any modifications. A single residue error means a reorder. Most suppliers can review your sequence for basic consistency, but the responsibility for the design is yours.
Compliance and labeling
Custom peptides intended for laboratory use should be labeled for research use only (RUO) and should not be marketed with clinical claims. If your project needs documentation for your institution, ask for full batch traceability. For peptides you plan to publish with, keep the COA, the sequence file and the batch number together in your lab records so that any reviewer can trace the material.
PEPMAKE offers custom peptide synthesis with sequence submission, purity selection, quantity selection and batch-level HPLC/MS documentation. When reviewing quotes, pair this with our peptide supplier red flags checklist.
A final sanity check on quotes
When the quotes arrive, read them side by side with the purity grade, net peptide content and scale normalized. Confirm the timeline includes purification and QC, and confirm which analytical methods are included in the price. A quote that is half the price of its peers at the same purity grade and scale is usually quoting less scope, not better value.
FAQ
What is custom peptide synthesis?
A service that builds a specific amino acid sequence and delivers purified, tested peptide material.
How long does it take?
Typically 1-3 weeks for short peptides, including QC and shipping.
What purity can I request?
From crude to 99%+ HPLC purity, depending on the sequence and scale.
What information do I need to provide?
The sequence, quantity, purity, modifications and any labeling requirements.