Synthesis and exon‐skipping properties of a 3′‐ursodeoxycholic acid‐conjugated oligonucleotide targeting dmd pre‐mrna: Pre‐synthetic versus post‐ synthetic approach

Steric blocking antisense oligonucleotides (ASO) are promising tools for splice modulation such as exon‐skipping, although their therapeutic effect may be compromised by insufficient delivery. To address this issue, we investigated the synthesis of a 20‐mer 2′‐OMe PS oligonucleotide conjugated at 3′‐end with ursodeoxycholic acid (UDCA) involved in the targeting of human DMD exon 51, by exploiting both a pre‐synthetic and a solution phase approach. The two approaches have been compared. Both strategies successfully provided the desired ASO 51 3′‐UDC in good yield and purity. It should be pointed out that the pre‐synthetic approach insured better yields and proved to be more cost‐effective. The exon skipping efficiency of the conjugated oligonucleotide was evaluated in myogenic cell lines and compared to that of unconjugated one: a better performance was determined for ASO 51 3′‐UDC with an average 9.5‐fold increase with respect to ASO 51.