29 Peptide / Oligo Synthesis CDMOs

What is peptide / oligo synthesis and when do you need it?

Peptide and oligonucleotide synthesis is the chemistry that builds your drug substance one residue at a time. For peptides that almost always means solid-phase peptide synthesis (SPPS), usually Fmoc chemistry, where amino acids are coupled in sequence on a resin, then the chain is cleaved, deprotected, and purified. For oligonucleotides, including antisense (ASO), siRNA, and aptamers, it is phosphoramidite chemistry on a synthesizer, with the chemical modifications (phosphorothioate backbones, 2'-OMe or 2'-MOE sugars, LNA, GalNAc conjugation) that give a modern oligo its stability and targeting. Different machines, same core idea: a defined molecule assembled chemically rather than expressed in a cell.

You reach for a dedicated synthesis CDMO once your candidate is real enough that the next batches need to be controlled, characterized, and eventually GMP. Early on a discovery group or a research-grade supplier can make milligrams for screening. The handoff to a CMC synthesis vendor typically lands as you scope IND-enabling toxicology, because the test article dosed in your GLP animals should match clinical material, and again as you build the clinical batch and the analytical package behind it. That is the moment crude purity, the impurity profile, and a release specification stop being academic.

The thing that surprises first-time sponsors is that the real work is rarely the coupling. It is purification and impurity control. A long peptide or a heavily modified oligo comes off the synthesizer as a mixture: the full-length product plus deletion sequences, truncations, and modification-related variants that differ from your target by a single residue or a single backbone substitution. Separating those by preparative reversed-phase HPLC (or ion-exchange for oligos), characterizing them by LC-MS, and proving batch-to-batch consistency is where most of the cost, the timeline, and the regulatory scrutiny actually sit.

What does a peptide / oligo synthesis CDMO actually do?

A synthesis CDMO owns the drug substance: it makes the molecule, purifies it, characterizes it, and (when you are clinical) releases it under GMP. On the peptide side that is SPPS scale-up from a few grams to kilos, choice of resin and coupling strategy, handling of difficult sequences and aggregation-prone stretches, cleavage and global deprotection, then preparative chromatography and lyophilization to a defined solid. Longer or cyclic peptides, disulfide-bridged sequences, and peptides with non-natural amino acids or lipidation each add their own wrinkles, which is why a vendor that runs a 12-mer linear peptide well is not automatically the right shop for a stapled or multiply-bridged one.

On the oligo side the vendor runs solid-phase phosphoramidite synthesis, handles the modified amidites your sequence calls for, performs deprotection and cleavage, and purifies by reversed-phase or anion-exchange HPLC, often with desalting and lyophilization to follow. Conjugation steps (GalNAc, lipid, peptide-oligo conjugates) are a distinct competency, and not every oligo house does them. Across both modalities the analytical work is the spine of the deliverable: identity and sequence confirmation, purity by HPLC, mass confirmation by LC-MS, counterion and water content, residual solvents and reagents, and for oligos the deconvolution of closely related impurities that a simple purity number hides.

What you are buying, in practice, is a drug substance you can defend in Module 3. That means a documented process, a release specification with justified acceptance criteria, characterized reference standards, a stability program, and an impurity story a reviewer will accept. A vendor that can make grams of clean material but cannot give you that package will slow your filing, not speed it. The strongest synthesis partners think about the spec and the impurity profile from the first development batch, not at the moment you ask for a certificate of analysis.

How do you choose a peptide / oligo synthesis CDMO?

Match the chemistry first, then the quality grade, then the practical things that decide whether your clinical supply lands on time. A vendor that is excellent at standard linear peptides may have never run a phosphorothioate-rich ASO, and an oligo house strong in siRNA may not do the lipidation your peptide needs. Score two or three candidates against the same written scope (sequence, modifications, scale, purity target, quality grade, timeline) so the quotes are comparing the same molecule, not three different interpretations of it.

Use this checklist when you compare vendors on BioBridgeX:

• Quality and GxP status: research-grade, non-GMP development, or GMP. The moment material goes into a patient (or into your GLP tox study as the registered test article), drug substance and its release testing must be GMP. Ask which agencies (FDA, EMA, PMDA) have inspected the site and what the findings were, because a clean inspection record is what lets you cite the work in a filing.
• Capacity and lead time: confirm a realistic slot, not a wish. Good synthesis suites book out, modified amidites and unusual amino acids have their own procurement lead times, and a difficult sequence can need several development runs before the process is fixed. Ask what historically causes slippage.
• Modality and indication fit: linear vs cyclic or stapled peptide, disulfide bridges, non-natural amino acids, lipidation; ASO vs siRNA vs aptamer, the specific backbone and sugar modifications, and any conjugation (GalNAc, lipid). Confirm the vendor runs your exact chemistry routinely.
• Scale fit across the program: a vendor whose clinical batch size also covers your eventual commercial need saves you a second tech transfer later. Forcing material onto a too-small or too-large process is a hidden cost.
• Region and regulatory track record: where the site sits, which regulators have audited it, and whether the vendor has supported filings in your target markets, not just made material.
• Analytical depth and data quality: purity by HPLC plus orthogonal LC-MS, sequence and identity confirmation, impurity identification and control, reference standard characterization, and a stability program. A clean purity number with no impurity story is incomplete.
• IP and confidentiality: who owns the process and any process improvements, how your sequence and data are protected, and clear terms before you disclose a proprietary sequence to a synthesis vendor.