BX LAB TECHNICAL ARTICLE
Established Chemistry Buys You a Smaller Regulatory Package
An industry consortium white paper says the quiet part: novel chemistry costs you more than synthesis time.
Key takeaways
The IQ Consortium says a less comprehensive biotransformation package may be adequate for well-established chemistry.
Plasma PK often does not reflect where an oligonucleotide is working, so tissue PK carries the argument.
Oligonucleotides rarely touch the usual metabolising enzymes and transporters, which simplifies clinical pharmacology.
A white paper worth reading twice
In 2025 the Innovation and Quality Consortium Nucleic Acids Working Group published a white paper in Nucleic Acids Research on how the industry actually develops siRNA and antisense drugs. It is not a marketing document — it is a group of drug developers agreeing on what they do and what they think regulators should expect. It is open access, and it contains one sentence that anyone choosing a backbone chemistry should read carefully.
The sentence
On biotransformation and tissue distribution work, the authors write that these studies are essential — "although a less comprehensive package may be adequate for well-established chemistry". Read that from the other side and it says something blunter: if you choose a modification nobody has characterised, you will pay for the characterisation. Novel chemistry does not just cost synthesis time. It costs a metabolite identification programme, a distribution study, and the reviewer questions that come with both.
Why oligonucleotides get this concession at all
The same paper explains the logic. Clinical pharmacology for oligonucleotides is less complex than for small molecules, because they are unlikely to interact with the common drug-metabolising enzymes or transporter proteins that generate most small-molecule interaction work. Their metabolism is largely nuclease-driven and, for a given chemistry, fairly predictable. That predictability is exactly what "well-established" means here — not that the chemistry is popular, but that its metabolic fate has already been mapped in public.
Plasma is the wrong place to look
The white paper puts particular emphasis on tissue pharmacokinetics for cases where plasma PK does not reflect therapeutic activity. This catches people out. An oligonucleotide can clear from plasma quickly and still be sitting in the liver doing its job for weeks. If your bioanalytical plan measures only what is easy to measure, it will describe a drug that is not the one you are developing.
What this means when you pick building blocks
There is a real trade-off, and it is not the one people usually argue about. A novel 2′ modification might buy potency. It also moves you out of the category the IQ paper describes and into the one where the full package applies. That may be worth it. But it should be a decision made with the regulatory cost visible, not discovered at the end of preclinical. If a 2′-MOE or 2′-O-Me gapmer with a GalNAc conjugate will do the job, the established route is cheaper in more ways than the price of the amidite.
The uncomfortable corollary
This is not an argument that novelty is bad, and we sell plenty of chemistry that is not established. It is an argument for knowing which side of the line you are standing on before you commit. Ask what has been published on the metabolic fate of the modification you are considering. If the answer is "not much", that is not a reason to stop — but it is a number in your budget that nobody has written down yet.
Turn the product name into a decision-ready specification
A purchasing name is only the starting point for a research material. Build the specification around exact chemical identity, form and assay basis. Define how identity will be confirmed and distinguish chromatographic purity from assay, concentration or active-content measurements. Add the attributes that could alter use, such as water, residual solvent, counterion, residual metals, known related substances or storage sensitivity. Acceptance limits should reflect the intended function rather than copying every available analytical result into a specification. Where a method is critical, record the technique, column or detection principle and sample preparation assumptions. This gives chemistry, analytical and procurement teams one shared definition of the material and reduces the chance that a technically correct but operationally unsuitable lot enters the project.
Qualify the material in the workflow that matters
A CoA can establish lot results against an agreed specification, but it cannot by itself prove performance in the intended research workflow. Plan a small, controlled qualification using a representative substrate, sequence, enzyme, reaction or analytical method. Include a suitable reference or previously accepted lot when available, keep preparation conditions comparable and predefine the observations that will trigger acceptance or investigation. Useful endpoints can include conversion, coupling efficiency, impurity formation, recovery, transcript integrity, conjugation yield or downstream signal, depending on the material. Record both the chemical result and practical behavior such as dissolution time, foaming, color change, precipitation or instrument delivery. This separates a material-quality question from a process-compatibility question and creates evidence that can support later lot-to-lot comparison.
Review process and scale risks before increasing quantity
Scale changes can expose risks that are not visible in a small research batch. For a research material, review handling, purification, analysis and scale-up before committing to a larger campaign. Estimate concentration, heat and mass-transfer needs, hold times, mixing limits, filtration area and the stability window of intermediates or prepared solutions. Identify the operations that control impurity rejection rather than assuming reaction yield alone will predict an acceptable isolated product. Raw-material availability and variability should be included in the route review, especially when a protecting-group reagent, specialty precursor or purification medium has a long lead time. A staged plan—feasibility, confirmation batch and then larger manufacture—provides checkpoints for analytical comparability, safety review and yield reconciliation while there is still room to adjust the process.
Build an analytical package that answers buyer questions
The useful documentation package should connect identity, purity and intended use. At minimum, align the specification and lot-specific Certificate of Analysis; then identify which supporting data are appropriate for the chemistry, such as HPLC or UPLC, LC-MS, high-resolution MS, NMR, water, residual solvents or inorganic-ion analysis. Chromatograms and spectra are most helpful when the material form, sample preparation and acceptance logic are clear. For complex or highly polar materials, a single percentage may not describe all relevant attributes, so note whether the result represents area purity, assay, concentration or another basis. Change control should cover shifts in route, critical starting material, purification approach, analytical method or manufacturing site when those changes could affect comparability. This framework helps technical, QA and procurement reviewers reach the same conclusion from the same evidence.
Use a structured request to shorten technical review
A complete inquiry for a research material should include the structure or unambiguous identifier, desired form, target quantity, expected future scale, intended use, target date and required documentation. Add known constraints: sensitive functional groups, prohibited solvents, metal limits, water sensitivity, shipping temperature, packaging preference or compatibility with an established method. If the request supports a regulatory submission, state the development stage and the documents expected, but do not assume that research-use or non-GMP material carries a qualification it does not have. Ask the supplier to identify open assumptions in the quotation and to separate confirmed specification items from values that still require method development. The resulting technical exchange is more efficient, and the final quotation can be tied to a material definition that is meaningful to scientists, procurement and quality reviewers.
Build a fit-for-purpose request
Before sourcing or scale-up, align the exact structure, intended workflow, target purity and assay basis, required form, storage conditions, quantity, timeline and documentation. If a catalog item does not match those requirements, a related analog, impurity standard, reference material or research-use custom route can be reviewed.
References
Technical context is supported by the peer-reviewed literature below.
- Christensen et al. (2025) Translational and clinical development of therapeutic siRNA and ASOs: current industry practices, perspectives, and recommendations. Nucleic Acids Research — IQ Consortium Nucleic Acids Working Group white paper (open access)
- Wan et al. (2014) Synthesis, biophysical properties and biological activity of second generation antisense oligonucleotides containing chiral phosphorothioate linkages. Nucleic Acids Research
- Iwamoto et al. (2017) Control of phosphorothioate stereochemistry substantially increases the efficacy of antisense oligonucleotides. Nature Biotechnology