Efficient Synthesis of 2’‐O‐Methoxyethyl Oligonucleotide‐Cationic Peptide Conjugates

Single‐stranded phosphorothioate (PS) oligonucleotide drugs have shown potential for the treatment of several rare diseases. However, a barrier to their widespread use is that they exhibit activity in only a narrow range of tissues. One way to circumvent this constraint is to conjugate them to cationic cell‐penetrating peptides (CPPs). Although there are several examples of morpholino and peptide nucleic acids conjugated with CPPs, there are noticeably few examples of PS oligonucleotide‐CPP conjugates. This is surprising given that PS oligonucleotides presently represent the largest class of approved RNA‐based drugs, including Nusinersen, that bears the 2’‐O‐methoxyethyl (MOE)‐chemistry. In this work, we report a method for in‐solution conjugation of cationic, hydrophobic peptides or human serum albumin to a 22‐nucleotide MOE‐PS oligonucleotide. Conjugates were obtained in high yields and purities. Our findings pave the way for their large‐scale synthesis and testing in vivo.