A credible custom-synthesis quotation is a process proposal, not a price multiplied by grams. When qualifying a custom peptide synthesis supplier for scale-up, I first ask what changed between the feasibility batch and the requested production quantity. Resin loading, mixing, coupling equivalents, cleavage volume, precipitation, preparative chromatography and lyophilization all scale differently. A sequence that gives 120 mg of clean material can become a poor gram-scale process when the crude impurity burden exceeds the purification window.
Freeze the molecular definition before the quote
Send the sequence in an unambiguous format and list every terminal group, D-amino acid, non-natural residue, isotope label, linker, lipid, fluorescent tag, disulfide bond and salt requirement. State whether the requested quantity means gross powder or net peptide content. Include the required purity method, counterion, residual-solvent limits, packaging configuration and intended research matrix. If two suppliers quote different structures under the same shorthand name, their prices are not comparable.
For sequences containing methionine, tryptophan, cysteine, asparagine, aspartic acid or aggregation-prone hydrophobic stretches, ask the chemist to identify likely failure modes. The useful answer is specific: oxidation, aspartimide formation, deletion sequences, incomplete deprotection, difficult resin swelling or poor cleavage recovery. “No problem” is not a development assessment.
Crude purity predicts purification cost
Request the crude analytical HPLC and mass spectrum from the feasibility lot before authorizing scale-up. Crude purity is not a release specification, but it shows whether the synthesis route produces impurities that preparative chromatography can separate. A 45% crude containing many well-separated peaks may be recoverable. An 80% crude with a deletion sequence co-eluting beneath the main peak may be harder.
Ask how the proposed resin substitution, coupling reagent, reaction monitoring and capping strategy were selected. At larger scale, poor mixing can create localized incomplete coupling. Simply extending reaction time does not always repair an aggregated resin bed. The supplier should define in-process checks and the decision point for recoupling or route adjustment.
Demand a mass balance, not only final yield
The quotation should distinguish theoretical synthesis scale, crude recovered mass, preparative load, purified pool, salt-exchanged material, lyophilized output and released net peptide. Yield losses often occur during transfer, filtration, desalting and lyophilization rather than synthesis. Without a stage-by-stage estimate, the buyer cannot tell whether a low final yield is chemically unavoidable or operational.
Purification capacity is a frequent hidden constraint. Confirm column size, maximum load, fraction strategy, pooling criteria and whether multiple purification cycles are included. A quote based on one optimistic preparative run can generate a change order after the crude material is already committed.
Analytical package for a scale-up lot
- Full analytical HPLC chromatogram, method conditions and integration table.
- Complete LC-MS spectrum with theoretical and observed mass.
- Peptide content or assay basis, not HPLC area purity alone.
- Water, counterion and residual solvents appropriate to the process.
- Sequence- or modification-specific tests such as free thiol, peptide mapping or optical purity.
- Sampling statement connecting bulk material and filled units.
If the peptide will be used quantitatively, amino acid analysis or another justified assay may be necessary. A “10 g, 98% HPLC” delivery can contain materially less than 10 g of peptide after water and counterion are considered. Put the calculation basis in the purchase specification.
Change control belongs in the commercial terms
Ask which changes require buyer approval: resin vendor, protected amino-acid source, synthesis site, purification method, salt exchange, lyophilization cycle, analytical laboratory or packaging component. Overseas suppliers sometimes treat these as routine purchasing decisions. For a research program comparing lots, an unreported process change can invalidate trend data.
The quotation should state what happens when purity, identity, quantity or delivery date fails. Define reprocessing rights, repeat synthesis, partial-lot acceptance, raw-data access and ownership of custom methods. Also clarify whether excess material can be sold to another customer and whether the sequence is treated as confidential.
Pilot scale is cheaper than rescuing a full batch
For a difficult sequence, use a staged order: feasibility, intermediate pilot, then target scale. Keep methods and reference material consistent across stages. Compare the impurity profile, not just the final purity number. A new impurity at pilot scale is an early warning even if the release result remains above 98%.
How long should custom synthesis take? The sequence and specification decide. Raw-material procurement, special-residue synthesis, method development, purification cycles, salt exchange, lyophilization and independent testing each add time. A very short promise may assume one-pass success and no confirmatory testing.
Before placing the order, ask the supplier to return a completed technical table showing molecular definition, synthesis scale, expected crude profile, purification plan, release tests, net-content basis, packaging, change control and failure remedy. That document gives procurement a firmer comparison than unit price and headline purity.