Synthesis of High-Quality Antisense Drugs. Addition of Acrylonitrile to Phosphorothioate Oligonucleotides: Adduct Characterization and Avoidance

Abstract

It is demonstrated that the acrylonitrile (AN) generated during the ammonolysis step of oligonucleotide manufacture selectively adds to thymine residue present in ISIS 2302 to give a full-length oligonucleotide in which thymine is replaced by an N3-cyanoethylthymine residue. Treatment of support-bound ISIS 2302 with a solution of triethylamine in CH3CN before ammonolysis is sufficient to prevent formation of this class of impurity.