Strain promoted click labeling of oligonucleotides on solid-phase support

Chemically modified oligonucleotides (ONs) are essential tools in molecular biology, diagnostics, and therapeutics. Strain-promoted azide-alkyne cycloaddition (SPAAC) offers an efficient and bioorthogonal method for ON functionalization. While SPAAC reactions on solid-phase support provide distinct advantages, particularly for the incorporation of lipophilic labels, factors influencing their efficiency remain poorly characterized. The interplay between the physicochemical properties of the modifying molecule, the nature of the solid support, and the labeling site within the ON chain has not been systematically evaluated. In this study, we systematically investigate how modifying molecule properties (size, polarity) and concentration, solid support type, labeling site within the ON chain, and reaction time influence efficiency of labeling. Our findings demonstrate that while polar modifying molecules react efficiently across all solid supports, lipophilic molecules can exhibit reduced reactivity on glass-based supports, particularly in positions close to the 3́-end of the oligonucleotide attached to the support. We further show that conjugation at the 5'-terminus consistently yields the highest efficiencies, with a gradual decline observed as the modification site approaches the 3'-end. A 1 mM concentration of labeling reagent was sufficient to achieve high yields on polystyrene support for all labels and on CPG 500 for the polar labels. The size of the modifying molecule had a lesser effect compared to other factors. The method also benefits from recovery and reusability of the unreacted label. These results enable the rational design of efficient ON labeling protocols on solid-phase support while minimizing reagent consumption, contributing to both cost-effectiveness and environmental sustainability.