Efficient introduction of phosphorothioates into RNA oligonucleotides by 3-ethoxy-1,2,4-dithiazoline-5-one (EDITH)

We recently reported on the use of 1,2,4-dithiazolidine-3,5-dione (DtsNH) and 3-ethoxy-1,2,4-dithiazoline-5-one (EDITH) as effective sulfurizing reagents for the preparation of phosphorothioate-containing oligodeoxyribo-nucleotides [Xu et al. (1996) Nucleic Acids Res., 24, 1602-1607]. One challenge in automated solid-phase synthesis of phosphorothioate-containing RNA is to develop sulfurization reagents that are effective in the presence of bulky 2'-OH protecting groups. The present study demonstrates that EDITH is exceedingly effective at low concentrations (0.05 M) and short reaction times (2 min) for the automated synthesis of oligoribonucleotides.