Controlled pore glass

Standard phosphoramidites (Bz-dA, Ac-dC, dmf-dG, dT and dB: dmf-isodG-CE phosphoramidite) and controlled pore glass (CPG) having standard residues were purchased from Glen Research (Sterling, VA), and AEGIS phosphoramidites (dZ, dP and dS) were purchased from Firebird Biomolecular Sciences (Alachua, FL). All oligonucleotides containing dZ, dP, dB and dS were synthesized on an ABI 394 DNA Synthesizer following standard phosphoramidite chemistry and as previously reported [4 (link)]. The CPGs having oligonucleotides were treated with 2.0 ml of 1 M 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in anhydrous acetonitrile at room temperature for 24 h to deprotect the p-nitrophenylethyl (NPE) group on the dZ nucleobase. Then the CPGs were filtered, dried and treated with concentrated ammonium hydroxide at 55°C for 16 h. After the removal of ammonium hydroxide, the oligonucleotides containing dZ, dP, dB and dS were purified by ion-exchange HPLC (solution A: 25 mM NaOH; solution B: 25 mM NaOH and 1.0 M NaCl). The fraction was neutralized by adding 2.0 M triethylammonium acetate (TEAA) buffer and the oligonucleotides were desalted using Sep-Pac® Plus C18 cartridges (Waters). Chromatograms for the three oligonucleotides following HPLC purification are shown in the electronic supplementary material.