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Identification of a Tricyclic PIII Chiral Auxiliary for Solid‐Supported Synthesis of Stereopure Phosphorothioate‐Containing Oligonucleotides

Since the recognition of oligonucleotides as a therapeutic modality, significant work has been devoted to improving therapeutic properties, including nuclease stability. Phosphorothioate (PS) modifications of phosphodiesters are one of the most explored chemical modification and integral to currently approved oligonucleotide therapeutics, including antisense oligonucleotides (ASOs) and short interfering RNAs (siRNAs). Insertion of sulfur into the phosphate bridge in an n‐mer leads to 2n isomeric mixtures of PSs, with different nuclease stability and protein‐binding properties. Efforts to create stereopure PS‐containing oligonucleotides has spurred interest in identifying new synthetic methods. Herein, work on a novel and practical tricyclic PIII chiral auxiliary and its application in solid‐supported synthesis of stereopure PS‐containing oligonucleotides is reported.