Streospecific substitution of oxygen-18 for sulfur in nucleoside phosphorothioates

Reaction of nucleoside phosphorothioates with N-bromosuccinimide in dioxane and H218O leads to the exchange of sulfur for oxygen-18. Using the Sp-isomers of adenosine 5'-O-(1-thiodiphosphate) and adenosine 3',5'-cyclic phosphorothioate, it can be shown by 31P NMR spectroscopy that this reaction proceeds with inversion of configuration yielding the Rp-isomers of [alpha-18O]ADP and [18O]cAMP, respectively. Adenosine 5'-O-(2-thiotriphosphate) and adenosine 5'-O-(3-thiotriphosphate) are likewise converted to [beta-18O]ATP and [gamma-18O]ATP although the stereochemistry of the former reaction has yet to be evaluated. With very slight modifications this reaction is applicable to all the common bases.