The synthesis of RNA 19a was carried out on a MerMade synthesizer at 1 μmol scale. The first nucleoside U at the 3′-end was introduced using phosphoramidite 1f, which carries the SoA linkage. The synthesis was conducted under typical RNA synthesis conditions except that the coupling time for the first nucleoside was slightly longer. Detailed conditions are provided in the Supporting Information. At the end of the synthesis, the 5′-ODMTr group was kept. The fully protected RNA can be represented with 2 except that there was no ac4C in the sequence (Scheme 1). Deprotection and cleavage were achieved in two steps. In the first step, the 2-CE groups were removed with 10% DBU in ACN at room temperature. At this time, the RNA was still on the solid support, which made removal of deprotection side products and excess reagents simple. The support was washed with ACN. In the second step, the support was suspended in dry DMSO and heated at 65 °C briefly to ensure that the RNA molecules on the support were in full contact with the solvent. The TBS group was then removed with fluoride. To retain the 5′-ODMTr group for the purpose of RNA purification, excess triethylamine was added first, and then followed by Et3N-3HF. Under these conditions, the silyl groups including those on the SoM and SoA groups were probably all removed, and a portion of the 2′-OTBS groups might have been deprotected as well. Assuming that all the silyl groups were removed, the RNA at this stage can be represented by 3 (except no ac4C). The mixture was then heated to 65 °C for 30 minutes, which are the typical conditions for the complete deprotection of 2′-OTBS groups in standard RNA synthesis methods. At this temperature, the remaining silyl groups, if any left, were removed, and the TBS-free and SoA groups as represented in 3 were cyclized giving fully deprotected RNA 4 (no ac4C). RNA 19a was purified using Glen-Pak TM under conditions used by standard RNA synthesis methods. Details can be found elsewhere. RP HPLC and MALDI MS analyses (see Supporting Information) indicated that the RNA could be cleaved from the support and the SoM groups could be completely removed under the non-nucleophilic conditions.