Phosphorothioate oligonucleotides: Largely reduced (N-1)-mer and phosphodiester content through the use of dimeric phosphoramidite synthons

Phosphorothioate oligonucleotides synthesized through an assembly of dimeric phosphoramidite synthons on controlled pore glass solid support show a significantly improved impurity profile compared to oligomers synthesized through a coupling of standard monomer phosphoramidites. A greater than 70% reduction of the (n-1)-mer population and a ca 50% reduction of phosphodiester linkages has been achieved.