The phosphite triester formed in the coupling step can be converted to the corresponding phosphorothioate triester by treatment with 0.2 M solution of phenylacetyl disulfide (PADS) in acetonitrile and 3-picoline (V V 1 1). Typically a 1.5-column volume of PADS solution is used and sulphurization is complete within 3 minutes at which time excess reagent is recovered from the reaction vessel by washing with acetonitrile.An alternative sulfur-transfer reagent is 3-amino-124-dithiazole-5-thione (ADTT also known as Xanthane Hydride) which is suitable for solid-phase synthesis.

Sulfurizing reagent used in the synthesis of oligonucleotide phosphorothioates.