Synthesis of Chemically Diverse siRNA‐Lipid Conjugates Enabled by Reversible Adsorption to Solid Support (RASS)

Small interfering RNAs (siRNAs) directly regulate gene expression and are, thus, attractive targets for clinical development to treat a variety of human diseases. While "naked" siRNAs are poor drug candidates, numerous chemical modifications of siRNAs have been developed to lower nuclease-sensitivity, increase cellular uptake, and enable cell-type-specific targeting. One class of modifications that has received attention is postsynthetic lipidation, as the pharmacokinetics of siRNA-lipid conjugates have been found to vary significantly based on the structure of the lipid moiety. While postsynthetic lipidation is a facile and effective means to render siRNAs more drug-like, most of these modifications occur in a single-step and in aqueous solution, engendering a limited chemical space. Herein, reversible adsorption of oligos onto a cationic solid support is demonstrated to facilitate postsynthetic, multistep modifications of single- and double-stranded siRNA in neat organic solvent to obtain siRNA-lipid conjugates with lipid moieties (e.g., long-chain alkyl thioethers, polyfluorinated biphenyl groups) that are challenging to incorporate using established postsynthetic lipidation procedures. RASS represents a rapid and convenient approach to generate siRNA-lipid conjugates encompassing a broad chemical space and ultimately a promising avenue to accelerate the discovery of potent siRNA therapeutics.