Synthesis of Modified Oligonucleotides

The oligonucleotides were synthesized on a 1 μmol scale using a DNA automated synthesizer (Applied Biosystems, Waltham, MA, USA, 392 DNA/RNA Synthesizer) with conventional phosphoramidite chemistry. The reagents were purchased from Glen Research (Sterling, VA, USA) and Sigma-Aldrich, and the synthesis was conducted using ultra-mild phosphoramidites (phenoxyacetyl-dA (Pac-dA), Tac-dG, Ac-dC, T), with 0.25 M 5-benzylthio-1H-tetrazole (BTT) in CH₃CN as an activator, 3% dichloroacetic acid (DCA) in CH₂Cl₂ as a deblocking solution, and 5% Tac₂O and 16% N-methylimidazole in THF as a capping reagent. The ODNs incorporating the original ^NPu and ^OPu were synthesized as previously reported [31 (link)]. Fully natural ODNs were purchased from Japan Bio Service Co., Ltd. (Osaka Japan).