PHARMACEUTICALS
DCA purity in oligonucleotide synthesis: Why the manufacturing route matters
Dr Christian Schulz of CABB and Professor Tobias Pöhlmann of XNA Pharma show why DCA quality determines oligonucleotide synthesis performance
Since the introduction of the phosphoramidite solidphase synthesis route for oligonucleotide therapeutics, manufacturing scales have evolved dramatically, from the nanomole and micromole range to multi-mole production levels. In parallel, the therapeutic scope of approved oligonucleotide drugs has expanded from rare diseases to indications affecting substantially larger patient populations.
In this context, Novartis’ inclisiran( Leqvio) represents a key milestone as the first oligonucleotide therapeutic to require truly largescale commercial manufacturing for the treatment of a highly prevalent primary hypercholesterolaemia.
A significant number of oligonucleotide-based therapeutics are currently being evaluated in clinical trials. Beyond therapeutic applications, oligonucleotides and their analogues are also extensively used in diagnostic assays, research applications and a variety of laboratory techniques.
The growing demand for these molecules in therapeutic and diagnostic applications has increased the need for reliable and cost-efficient methods for their synthesis and chemical modification that meet stringent pharmaceutical quality requirements.
Based on the current development pipeline targeting prevalent diseases and historical success rates of oligonucleotide therapeutics, future demand for oligonucleotide API volumes may exceed global solid-
Figure 1- Comparison of percentages of critical related substances
1.03 %
DeTrityl Ultrapure
DeTrityl Ultrapure
n-1 0.61 % ± 0.12 %
n-2 0.25 % ± 0.04 %
Depurination 0.16 % ± 0.04 %
phase manufacturing capacity within a few years. 1
The process mass intensity( PMI) associated with oligonucleotide API manufacturing at scale is very high. To reduce costs, increase capacity and improve sustainability while safeguarding pharmaceutical quality standards, there is a clear need to optimise all process parameters, including solid support loading, resin properties, reagent quality and solvent selection.
Cumulative impurity burden
Dichloroacetic acid( DCA) removes the dimethoxytrityl( DMT) protecting group from the 5 '-hydroxyl moiety prior to each nucleoside coupling cycle. In a 20-mer sequence, the growing chain undergoes 20 sequential exposures to the
1.48 % 1.49 %
Asian DCA Grade 1
Asian DCA Grade 1
0.86 % ± 0.1 %
0.36 % ± 0.05 %
0.25 % ± 0.04 %
Asian DCA Grade 2
0.93 % ± 0.09 %
0.34 % ± 0.1 %
0.21 % ± 0.02 %
Asian DCA Grade 2
reagent and its associated impurity profile. Contaminants therefore act cumulatively, not in isolation, and their effects on sequence fidelity are additive across the synthesis cycle.
Consequently, DCA purity is critical, as impurities may be carried through the synthesis process and lead to the formation of undesired or truncated oligonucleotide sequences. Such related substances, including n-1 species or depurinated products, are difficult to remove in downstream processing and negatively impact overall yield, purity, and cost. Certain contaminants present in DCA, including chloral hydrate, glyoxylic acid, free chloride and formaldehyde, have been identified as potential causes of failed oligonucleotide synthesis. 2
SEP / OCT 2026 SPECCHEMONLINE. COM
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