Synthesis of Antisense Oligonucleotides:  Replacement of 3H-1,2-Benzodithiol-3-one 1,1-Dioxide (Beaucage Reagent) with Phenylacetyl Disulfide (PADS) As Efficient Sulfurization Reagent:  From Bench to Bulk Manufacture of Active Pharmaceutical Ingredient

It is demonstrated that phosphorothioate oligodeoxyribonucleotides can be synthesized on scales from 1 μmol to 150 mmol using phenylacetyl disulfide (PADS) as an efficient and economical replacement for Beaucage reagent. A 0.2 M solution of PADS in a mixture of 3-picoline and acetonitrile (1:1 v/v) as solvent with 60−120 s contact time efficiently (>99.6%) sulfurizes phosphite triesters to phosphorothioate triester linkages. Phenylacetyl disulfide reagent is inexpensive and scaleable and is currently being used by us for the manufacture of antisense phosphorothioate oligodeoxyribonucleotide active pharmaceutical ingredients (API).