Efficient and Simple Solid-Phase Synthesis of Short Cyclic Oligodeoxynucleotides Bearing a Phosphorothioate Linkage

Only one additional step is required to extend oligonucleotide synthesis to generate cyclic oligonucleotides by standard automated phosphoramidite chemistry. After 5′-iodination, cleavage from the solid support yields phosphorothioate-bridged compounds 1, which are under investigation as potentially bioactive molecules, in 40–80 % yields.