Peptide-drug and peptide-protein conjugates
Technical scope, quality level, batch documents and delivery requirements can be configured according to project stage.
Designed for biological research and industrial applications, not intended for individual clinical or medical purposes.
Advanced peptide conjugation for targeted delivery, tracking, functional studies and drug development.
Project Discussion
Share your target sequence, purity, scale, modification, delivery format and documentation requirements. Quantai will review feasibility and respond with a practical quotation route.
Core Capabilities
PEG, lipid, dye, isotope and biotin conjugation
Technical scope, quality level, batch documents and delivery requirements can be configured according to project stage.
Click chemistry and thiol-maleimide strategies
Technical scope, quality level, batch documents and delivery requirements can be configured according to project stage.
Cleavable and non-cleavable linker systems
Technical scope, quality level, batch documents and delivery requirements can be configured according to project stage.
Typical Workflow
1Requirement review
2Technical feasibility
3Quotation and timeline
4Synthesis or process execution
5QC documentation
6Shipment and follow-up
| Development Stage | Our Peptide Support |
|---|---|
| Concept & Feasibility | Peptide design strategy, sequence optimization and feasibility assessment |
| Discovery Research | Custom peptide synthesis, targeting peptide design and functional screening support |
| Lead Optimization | Peptide modification, conjugation strategy and structure-function optimization |
| Process Development | Route optimization, process robustness and impurity control strategy |
| GMP Manufacturing | GMP-compliant peptide synthesis, quality documentation and batch release support |
Technical Notes
Maleimide and thiol coupling
The reaction between a maleimide and a free thiol is the workhorse of peptide conjugation: fast, high-yielding, and selective for cysteine at mildly acidic to neutral pH. Above roughly pH 7.5 the maleimide begins to react with amines as well and selectivity is lost. The peptide's cysteine must be free rather than already in a disulfide, so material stored without a reducing agent may need reduction and clean-up before coupling. The resulting thioether is stable, though it can slowly exchange with other thiols in complex biological media.
NHS ester and amine coupling
N-hydroxysuccinimide esters acylate primary amines, meaning the peptide N-terminus and every lysine side chain. That makes the chemistry easy and the product heterogeneous unless there is only one amine present. The reagent also hydrolyses in water in competition with the coupling, so buffer choice matters and amine-containing buffers such as Tris cannot be used. Where site-specificity is required, either the peptide is designed with a single available amine or a thiol-based route is used instead.
Click chemistry
Azide-alkyne cycloaddition is bio-orthogonal: neither partner reacts with anything normally present on a peptide, so the coupling site is defined entirely by where the handle was installed. Copper-catalysed reactions are efficient but the catalyst can damage sensitive residues and must be removed afterwards. Strain-promoted reactions using cyclooctyne reagents avoid copper altogether at the cost of a larger, more hydrophobic handle. Both require the handle to be introduced during synthesis, so this route is chosen at the design stage rather than later.
Carrier proteins and hapten density
KLH is the usual carrier for immunisation because of its size and immunogenicity, and BSA or ovalbumin are used for the screening assay so that anti-carrier antibodies do not appear as false positives. Hapten density, the average number of peptides per carrier, influences the response: too low gives weak immunogenicity, too high can mask the peptide or reduce carrier solubility. Density is estimated after conjugation rather than assumed from the input ratio.
Characterising a conjugate
Conjugates are heterogeneous by nature, so characterisation describes a distribution rather than a single species. Dye-to-peptide ratio is calculated from absorbance at the dye maximum and the peptide, with a correction for the dye's own absorbance in the peptide region. Peptide-to-carrier ratio for protein conjugates is estimated by mass shift, amino acid analysis or a reagent-specific assay. Free, unconjugated payload is removed by desalting, dialysis or chromatography, and confirming its absence is part of release rather than an optional extra.
What You Receive
- Conjugate purified from unreacted peptide and free payload
- Ratio data appropriate to the conjugate type, such as dye-to-peptide or hapten density
- Analytical confirmation of the conjugation chemistry as executed
- Description of the linker, attachment site and coupling conditions used
- Handling and storage guidance for the conjugate as supplied
Typical Applications
Antibody generation — Peptide-carrier immunogens with a matched screening conjugate on a different carrier, so that the assay measures anti-peptide rather than anti-carrier response.
Imaging and detection probes — Dye or biotin conjugates for microscopy, flow cytometry and capture assays, with the ratio characterised and the attachment site chosen away from the binding face.
Targeted delivery constructs — Peptide-payload conjugates where the linker is chosen for whether and where the payload is intended to be released.
Surface immobilisation — Conjugates designed for attachment to beads, plates or sensor surfaces, where linker length and orientation determine whether the peptide remains accessible.
Frequently Asked Questions
Which carrier protein should I use for antibody production?
KLH is the usual choice for immunisation because its size and immunogenicity give a strong response. Use a different carrier, commonly BSA or ovalbumin, for the screening assay. If both use the same carrier, antibodies raised against the carrier will appear as positives and the screen will not tell you what you need to know.
Where should the conjugation site go?
Away from the region that has to stay recognisable. For an epitope peptide that usually means adding a cysteine at whichever terminus is not part of the epitope. Where the peptide corresponds to an internal region of a protein, the terminus that faced into the protein is generally the safer attachment point.
My peptide has no cysteine. Can it still be conjugated?
Yes. A cysteine can be added at either terminus during synthesis, which is the cleanest option and keeps the site defined. Alternatively, amine-directed chemistry can be used, though with several lysines present the product will be a mixture of attachment sites. If the sequence has not been made yet, adding the handle at the design stage is much the better route.
How is the dye-to-peptide ratio determined?
From absorbance measurements at the dye maximum and in the peptide region, applying the dye's correction factor for its absorbance at the peptide wavelength. Skipping that correction systematically overstates the peptide concentration and therefore understates the ratio.
Should the linker be cleavable?
Only if the payload has to be released. A cleavable linker adds a failure mode, since premature release lowers what reaches the target and can cause effects where it is not wanted. For imaging and detection, where the payload should stay attached, a stable linker is the appropriate choice.
How do I know free dye has been removed?
Unconjugated payload is removed by desalting, dialysis or chromatography depending on the size difference, and its absence is confirmed analytically rather than assumed from the clean-up step. Residual free dye is a common cause of high background, and it is worth confirming before an unexplained background is attributed to the biology.
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