Phosphorothioate oligonucleotides manufactured by standard phosphoramidite techniques using 2′-deoxyadenosine-or 2′-O-(2-methoxyethyl)-5-methylcytosine-loaded solid supports contain branched impurities consisting of two chains linked through the exocyclic amino group of the 3′-terminal nucleoside of one chain and the 3′-terminal hydroxyl group of another via a P (O) SH group. These impurities are not produced when a ...
