Development of siRNA for therapeutics: Efficient synthesis of phosphorothioate RNA utilizing phenylacetyl disulfide (PADS)

Efficient synthesis of phosphorothioate RNA (PS-RNA) is demonstrated by using phenylacetyl disulfide (PADS) in a mixture of pyridine and acetonitrile (1:1, v/v) for 3 min. Sulfurization is achieved with >99.8% stepwise efficiency. This reagent also performs efficiently during synthesis of RNA containing PS:PO mixed backbone.