SYNTHESIS OF OLIGO(DEOXYRIBONUCLEOSIDE PHOSPHORODITHIOATE)S BY THE DITHIAPHOSPHOLANE APPROACH

A novel method of synthesis of oligo(deoxyribonucleoside phosphorodithioate)s (S-2-ODNs), based on the ring-opening condensation of nucleoside 3'-0-(2-thiono-1,3,2-dithiaphospholane)s with 5'-O-deprotected nucleosi(ti)des in the presence of a strong organic base such as DBU, is presented. The process has been adapted to the requirements of automated solid-phase oligonucleotide synthesis with a relatively short condensation step (5 min) and reasonable step-yield(>95%). N-Methylpyrrolidin-2-ylidenyl (Pya) was found to be the group of choice for the protection of reactive aminofunctions of nucleobases in nucleotide substrates. Sarcosine-containing linker (LCA CPG SAR) was employed due to its known resistance to cleavage by DBU. Several medium-size S-2-ODNs were prepared by this approach. Their identity and purity was confirmed by means of P-31 NMR, gel electrophoresis, and mass spectrometry. It has been demonstrated that, contrary to a recent report, S-2-ODNs are not degraded by DNaseI.