Site-selective side-chain functionalization for defined peptide labeling and conjugation.
At Bio-Synthesis, we provide side-chain peptide functionalization to deliver site-defined, reproducible peptide conjugates. Using residue-selective chemistry and orthogonal handle strategies, we enable precise labeling, stable linkages, and consistent results across discovery, assay, and conjugate workflows.
In addition to cysteine-, lysine-, and tyrosine-selective chemistry, we support Asp/Glu carboxylate modification (amide/lactam), Ser/Thr hydroxyl chemistry (including phosphorylation and O-glycosylation), and orthogonal handles for click/ligation (azide/alkyne, DBCO/BCN, carbonyl).
Choose a category below, or send your sequence and payload and we’ll recommend the most controlled approach.
Compared with non‑selective labeling approaches, residue‑selective and handle‑based strategies provide defined stoichiometry, improved batch consistency, and clearer biological interpretation.
Unlike generic peptide modification services, we support both native‑residue selectivity and engineered handle–based precision conjugation to reduce heterogeneity and improve reproducibility.
Best for: Site-specific labels, payload conjugation, cyclization, stable thioether designs.
Best for: Labeling/PEGylation, lactam bridges (Lys–Asp/Glu), solubility tuning.
Best for: Late-stage labeling when Cys is unavailable; orthogonal aromatic targeting.
Best for: Macrocyclization (side-chain/terminus-to-side-chain) and stable amide-based conjugates.
Best for: Signaling mimics, glyco-/phosphopeptide tools, binding and kinase assays.
Best for: Orthogonal, modular conjugation for probes and PDC-style architectures.
Side-chain functionalization is often combined with cyclic architectures and orthogonal handles for controlled conjugation. Explore these related capabilities:
A practical decision flow used in peptide conjugation projects: define the goal → choose the most controllable site → confirm risks and QC.
Start with the functional objective. Chemistry selection should follow the goal—not the other way around.
Prefer a unique, solvent-exposed residue away from the pharmacophore. If none exists, introduce an orthogonal handle.
Before committing to scale, check the usual failure modes and ensure the analytical plan is aligned to the intended use.
Common risks
QC alignment
For discovery workflows, we typically recommend single-site modification with LC–MS confirmation. For conjugates or regulated studies, expanded documentation/QC can be added.
Specified amount and target purity aligned to your application.
Analytical HPLC + MS (or HRMS) confirmation with chromatograms.
COA summarizing identity and purity; additional characterization available.
Single-site dyes, biotin, and tags for imaging, pull-downs, and assays.
Defined attachment points for payload/linker control and reproducible activity.
Systematic placement of modifications to probe binding, conformation, and protease resistance.
Site-selective peptide modification is controlled chemistry performed at a defined residue (or engineered handle) to produce a single, reproducible conjugate. For peptides, this is most often achieved via a single cysteine or an orthogonal handle (azide/alkyne, DBCO/BCN, carbonyl) to avoid mixed products from multiple reactive sites.
Choose a site that is unique (or can be made unique), solvent-exposed, and located away from binding/active motifs. If your sequence contains multiple Lys (or other competing residues), introduce a single Cys or click-ready handle for true single-site control, then confirm by LC–MS that only the intended modification state is present.
Side-chain functionalization is the installation of a defined chemical group on a specific amino-acid side chain (or an introduced handle) to enable labeling, conjugation, cyclization, solubility tuning, or payload attachment while keeping the peptide backbone sequence unchanged.
No. Cys/Lys/Tyr are common targets, but additional strategies modify Asp/Glu carboxylates, Ser/Thr hydroxyls (including phosphorylation and O-glycosylation), and introduced orthogonal handles (azide/alkyne, DBCO/BCN, aldehyde/ketone) for click or ligation chemistry.
Start with the functional requirement (label/payload/linker), then choose a residue that is unique or can be made unique, is solvent-exposed in your active conformation, and is away from the pharmacophore. When site specificity is critical, introduce a single Cys or an orthogonal handle.
Provide the sequence, desired modification or payload, target residue/position (if known), intended application (assay, imaging, PDC/ADC-like), and purity/QC needs. If you want a free N- or C-terminus, specify that explicitly.
We can recommend protection strategies, selective handle introduction, or redesign (e.g., single-Cys/handle) to reduce mixed products. Analytical LC-MS monitoring is used to confirm modification state.
Typical QC includes analytical HPLC purity and MS identity confirmation with a COA. Additional characterization (HRMS, peptide mapping, stability, or functional testing support) can be added based on your application.
Share your sequence, desired label/payload, target residue/position (if known), and intended application. We’ll recommend a practical modification strategy and QC plan.
Selected references on site-selective bioconjugation and residue-targeted chemistry.
We can tailor a reading list to your PTM (phospho, glyco, acetyl, methyl, UBL) and assay type on request.
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