BPC-157 10mg · Research brief

What Is Custom Peptide Synthesis? Specs and Turnaround

Real Peptides Research TeamEditorial

Updated September 29, 20269 min read

47 WORDS

Short answer

Two vials carrying the same sequence and the same 98% purity figure can hold measurably different amounts of peptide. The purity number describes a chromatogram. It says nothing about how much of the white powder in the vial is peptide rather than counterion salt and bound water.

Key takeaways

Custom peptide synthesis is quoted per project because length, purity grade, modifications and scale each change the cost independently.
Fmoc solid-phase peptide synthesis builds the chain from C-terminus to N-terminus on a resin, a method introduced by Robert Bruce Merrifield in 1963.
HPLC purity and net peptide content are different measurements, and only net peptide content tells you how much peptide is actually in the vial.
Peptides purified in a TFA gradient arrive as hygroscopic TFA salts, so counterion exchange to acetate matters for sensitive cell culture work.
Stepwise chemical synthesis becomes impractical above roughly 50 residues, at which point native chemical ligation or recombinant expression is the route.
Supplier quality is judged by raw analytical files and contractual remedies for off-spec batches, not by the country printed on the invoice.

We have quoted, reviewed and rejected a lot of synthesis specifications over the years. The pattern barely changes: projects fail on the spec sheet, not on the chemistry.

What is custom peptide synthesis?

Custom peptide synthesis is the made-to-order chemical assembly of a peptide from a sequence you supply, built one amino acid at a time on a solid resin support, then purified and analysed against an agreed specification. Most orders are linear chains under roughly 30 residues. Purity grade, modifications, scale and turnaround are quoted per project.

The common oversimplification is that custom peptide synthesis simply means a peptide that is not in the catalogue. In practice the sequence is the easy part. The specification wrapped around it, purity grade, counterion, modifications, scale and analytical documentation, decides whether the material works in your assay. This piece covers how the build runs, which spec lines matter most, what stretches turnaround, and how to compare suppliers across regions.

From resin to lyophilised powder: how the build runs

Almost every routine custom peptide synthesis run today uses Fmoc solid-phase peptide synthesis (SPPS), the method Robert Bruce Merrifield introduced in 1963 and received the 1984 Nobel Prize in Chemistry for. The peptide grows while anchored to an insoluble polymer resin, which means excess reagent and by-product get washed away between steps instead of separated out later.

The cycle repeats. Strip the Fmoc protecting group from the growing chain with piperidine in DMF, activate the next amino acid (HBTU, HATU, or DIC with Oxyma are standard), couple it, wash, repeat. The chain builds from the C-terminus toward the N-terminus, the opposite direction to ribosomal protein synthesis in a living cell. Once the sequence is complete, a trifluoroacetic acid (TFA) cleavage cocktail containing scavengers such as triisopropylsilane and water releases the peptide from the resin and strips the side-chain protecting groups in one step. The crude material is precipitated in cold ether, purified by reverse-phase HPLC on a C18 column with a water and acetonitrile gradient, then lyophilised to a dry powder.

Here is the consequence that drives pricing: no coupling step is perfectly efficient. Small losses compound with every residue, so deletion sequences, chains missing a single amino acid, accumulate as the peptide lengthens. Crude purity falls with chain length. That is why a 40-mer costs far more per milligram than a 10-mer at the identical purity grade.

Our team has reviewed a great many crude chromatograms. Length, not exotic chemistry, is what usually wrecks a yield.

The spec line most buyers never check

Purity and peptide content are two different numbers, and only one of them tells you how much peptide is in the vial. HPLC purity is an area percentage from the chromatogram: of everything that eluted and absorbed at 214 or 220 nm, what fraction was your target peak. Net peptide content, measured by amino acid analysis or nitrogen determination, tells you what fraction of the powder mass is actually peptide.

The gap between those two figures is real and it is routinely ignored. Peptides purified in a TFA gradient are isolated as TFA salts, and lyophilised TFA salts are hygroscopic, so vial mass includes counterion and bound water alongside peptide. A vial labelled 10 mg at 98% HPLC purity does not contain 10 mg of peptide. For anything quantitative, binding affinity, IC50 determination, a mass spectrometry standard curve, that discrepancy moves your numbers in a direction you cannot see.

Two requests fix most of it. Ask for net peptide content on the certificate of analysis, not just an HPLC percentage. And if the material is going into sensitive primary cells, ask for counterion exchange to acetate or hydrochloride, because residual TFA is cytotoxic in culture at surprisingly low concentrations and is a silent source of assay noise.

This is the single most common error we see in custom peptide synthesis orders. The buyer negotiates hard on purity grade, accepts the default TFA salt without comment, then weighs out by the vial label. The chemistry was fine. The arithmetic was not.

Modifications, difficult sequences and what stretches the timeline

Three variables drive turnaround: chain length, modification count, and how badly the sequence wants to aggregate on the resin. A short unmodified linear peptide at desalted or 95% grade is routine production work, typically quoted in a couple of weeks. Three disulfide bridges, a fluorophore and a gram-scale batch is a different project with a different calendar.

Modifications a custom peptide synthesis service will normally quote on:

N-terminal acetylation and C-terminal amidation, which neutralise the charged termini and better mimic the native protein environment
Fluorescent labels including FITC, 5-FAM, TAMRA and cyanine dyes, plus biotin for pull-down and streptavidin capture work
Phosphorylated serine, threonine or tyrosine residues for kinase assays and antibody generation
Cyclisation by head-to-tail linkage, side-chain lactam bridge or disulfide bond, which raises protease resistance
D-amino acids, unnatural residues, PEGylation and stable isotope labels for quantitative proteomics

Difficult sequences form their own cost category. Runs of arginine, long hydrophobic stretches and beta-sheet-prone segments cause the resin-bound chain to aggregate, coupling efficiency collapses, and the crude trace comes back as a smear rather than a peak. Pseudoproline dipeptides, backbone amide protection and elevated-temperature or microwave-assisted synthesis are the standard remedies, and every one of them adds cost.

Above roughly 50 residues, stepwise SPPS stops being sensible. Native chemical ligation, joining two purified fragments at a cysteine junction, or recombinant expression in a bacterial system takes over.

We have watched more timelines slip on one unflagged cysteine pair than on any other detail in a quote.

What buyers actually argue about when comparing suppliers

Read any research procurement discussion and the complaints about custom peptide synthesis companies are remarkably consistent: delivered purity not matching the quoted grade, net peptide content left vague, silence after the deposit clears, and turnaround estimates that slip without notice. Threads about custom peptide synthesis on Reddit rarely argue about chemistry. They argue about documentation and communication.

Geography matters less than process. Custom peptide synthesis companies operate across the USA, the UK, Canada, Australia, India and China, and plenty of suppliers with a local sales office broker the actual synthesis somewhere else entirely. Large catalogue houses, including MilliporeSigma under the Sigma-Aldrich brand and Thermo Fisher Scientific, run custom programmes alongside their listed products, which buys you procurement infrastructure and standardised paperwork. Smaller specialist labs often win on responsiveness, small-batch flexibility and the ability to put you on a call with the chemist who will run your sequence.

Four questions separate suppliers faster than any brochure. Where is the synthesis physically performed? Will you release the raw HPLC trace and mass spectrometry file rather than a summary sheet? Is net peptide content included or billed separately? And what happens, contractually, when a batch misses spec?

One compliance point stated plainly: research peptides are research-use-only materials, not FDA-approved drugs, and are never supplied for human or veterinary consumption. Anyone with a health question about an animal should talk to their veterinarian, and human health questions belong with a licensed physician, not a peptide supplier.

Custom peptide synthesis routes compared

Four routes cover nearly every custom peptide synthesis request that lands in a quote inbox. This table shows what each route suits, and where it stops making sense.

Route	Best suited to	Turnaround pattern	Documentation to demand	Bottom line
Catalogue peptide, off the shelf	Well-known sequences already stocked in standard vial sizes	Ships immediately from inventory	Batch-specific COA with HPLC trace and mass spec	Cheapest and fastest route, but you accept the stocked purity grade, salt form and vial size without negotiation
Standard custom SPPS, desalted or 95% grade	Screening panels, antibody immunogens, preliminary binding work	Routine, usually quoted in weeks rather than months	HPLC purity, ESI-MS or MALDI-TOF confirmation of molecular weight	The workhorse option, and adequate for most qualitative research where absolute peptide mass is not the readout
High-purity custom SPPS with modifications	Quantitative assays, cell culture, labelled probes, cyclised or phosphorylated sequences	Extended, driven by modification count and purification passes	Purity above 98%, net peptide content, counterion identity, full raw data files	The right specification when the number you publish depends on knowing exactly what is in the vial
Ligation or recombinant expression	Chains beyond roughly 50 residues, small proteins, folded domains	Longest of the four, with folding and refolding steps	Sequence verification, endotoxin data where relevant, purity and identity	Necessary once stepwise chemistry breaks down, and priced accordingly, so confirm the length threshold with the chemist before committing

What If: Synthesis Order Scenarios

What if the delivered peptide will not dissolve?

Check the sequence composition and the theoretical isoelectric point before assuming the batch is faulty. Peptides with a net charge near neutral at your buffer pH are the hardest to solubilise, and hydrophobic sequences often need a small volume of DMSO, acetic acid or ammonium bicarbonate before dilution into aqueous buffer. Sonication in a cold bath helps break up aggregates. If the powder still refuses to go into solution, request the supplier's solubility notes for that specific batch, since they will have handled the crude material.

What if the mass spectrum is correct but HPLC shows extra peaks?

Suspect isomers rather than the wrong molecule, because several common by-products share the exact mass of the target. Racemisation during coupling produces diastereomers with identical mass and different retention times. Scrambled disulfide connectivity in a multi-cysteine peptide does the same. Methionine oxidation adds 16 Da and is easy to spot, but aspartimide formation is not. Ask for the analytical method details and, where connectivity matters, for peptide mapping to confirm which cysteines actually paired.

What if I need the identical batch quality again next year?

Agree reference-batch terms at the time of the first order, not at reorder. Ask the supplier to retain a reference sample and the original chromatogram so the next lot can be compared against a real baseline rather than a specification range. Batch-to-batch variation in custom peptide synthesis shows up most in net peptide content and residual solvent, which both shift with purification and lyophilisation conditions. Buying a larger single batch is often cheaper than two matched smaller ones.

The unglamorous truth about purity claims

Here is the honest answer: a purity percentage printed on a label with no chromatogram behind it is a marketing number, not an analytical result. Purity is meaningless without the method, the detection wavelength, the gradient and the raw trace. A supplier who will not send the HPLC file and the mass spectrum is asking you to take chemistry on trust, and in research procurement that is the one thing you never do. Ask for the data files before the deposit, not after the delivery.

Our own catalogue is built on the same logic, with small-batch synthesis, exact amino-acid sequencing and per-batch documentation available through our certificates of analysis rather than on request. Researchers comparing options can browse the full peptide collection, including well-characterised compounds such as BPC-157, TB-500 and GHK-Cu, or check shipping and coverage details before ordering.

Custom peptide synthesis rewards the buyer who treats the quote as a technical document rather than a price. The sequence you send is the least interesting thing about the order, because any competent lab can build it. What separates a usable batch from an expensive disappointment is everything written around that sequence: the salt form, the content assay, the release criteria and the remedy when a run misses. Specify those four things and the chemistry almost takes care of itself.

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Questions

Custom peptide synthesis is the made-to-order chemical assembly of a peptide from a sequence the customer supplies. The chain is built one amino acid at a time on a solid resin using Fmoc chemistry, cleaved, purified by reverse-phase HPLC and lyophilised. Purity grade, modifications, salt form and scale are agreed before the run begins.

Turnaround depends on length, modifications and purity grade rather than order size. Short unmodified linear peptides at standard grade are routine and usually quoted in weeks. Multiple disulfide bridges, fluorescent labels, cyclisation or chains beyond roughly 50 residues extend the timeline considerably because they require extra purification and folding steps.

Pricing is quoted per project, usually driven by residue count, purity grade, scale in milligrams or grams, and each modification added. Costs vary widely between suppliers and regions, so a like-for-like comparison requires identical specifications on every quote, including whether net peptide content analysis is included or billed separately.

Most can, but not all with equal ease. Runs of arginine, long hydrophobic stretches and beta-sheet-prone segments aggregate on the resin and drive coupling efficiency down. Above roughly 50 residues, stepwise synthesis becomes impractical and native chemical ligation or recombinant expression is used instead. Send the sequence for a feasibility check before budgeting.

Desalted or 95% grade is generally adequate for antibody immunogens and early screening where absolute quantity is not the readout. Quantitative work such as binding affinity, IC50 determination or mass spectrometry standards calls for higher purity plus net peptide content data. Paying for 98% purity without knowing peptide content solves only half the problem.

A catalogue peptide ships from existing inventory at a fixed purity grade, salt form and vial size. Custom synthesis is produced to your specification, which means you control sequence, modifications, counterion, scale and release criteria. Catalogue items are faster and cheaper; custom orders exist when the stocked specification will not support the experiment.

Quality tracks process and documentation, not country of origin. Excellent and poor suppliers exist in every region, and many companies with a local office subcontract the actual synthesis elsewhere. Judge suppliers on where the chemistry is physically performed, whether raw HPLC and mass spectrometry files are released, and what the contract says about off-spec batches.

Large catalogue suppliers such as MilliporeSigma, which carries the Sigma-Aldrich brand, and Thermo Fisher Scientific offer procurement integration, standardised documentation and established ordering systems. Smaller specialist laboratories typically compete on responsiveness, small-batch flexibility and direct technical access to the chemist. The right choice depends on whether you need purchasing convenience or sequence-level problem solving.

Look for the HPLC chromatogram with the method and detection wavelength stated, a mass spectrometry result confirming the molecular weight, the net peptide content figure, the counterion identity, and the batch or lot number. A percentage printed with no supporting trace is not analytical evidence. Request the raw data files before placing the order.

Reverse-phase purification uses trifluoroacetic acid in the mobile phase, so the peptide is isolated as a TFA salt by default. It matters in two ways: the counterion and bound water add to vial mass, and residual TFA is cytotoxic to sensitive cells in culture. Salt exchange to acetate or hydrochloride is available on request.

That depends entirely on what was written into the quote. Reputable suppliers will re-purify, resynthesise or refund against pre-agreed acceptance criteria. Confirm the remedy in writing before payment, along with who covers freight on a returned batch, because verbal assurances are difficult to enforce across borders.

No. Research-use-only peptides are not FDA-approved drugs and are not supplied for human or veterinary consumption. They are intended for laboratory research by qualified personnel. Anyone with a health question concerning an animal should talk to their veterinarian, and human health questions should be directed to a licensed physician.

RESEARCH USE ONLY · NOT EVALUATED BY THE FDA