Synthesis of cyclic oligodeoxyribonucleotides via the ‘filtration’ approach

The synthesis of cyclic di-, tri-, tetra-, penta- and hexa-thymidylic acids (16; n = 2, 3, 4, 5 and 6) and the cyclic hexadeoxyribonucleotide [d(CpCpTpApGpGp)], via the "filtration" approach, is reported. Some of the physical properties of the cyclic oligonucleotides are discussed, and their susceptibility to digestion in the presence of phosphorylytic enzymes has been studied.