Synthesis of Rp and Sp [alpha-18O]ADP from Sp and Rp beta-cyanoethyl-adenosine 5'[1-thiodiphosphate]. 
The reaction of adenosine 5'[1-thio-2-cyanoethyl diphosphate], beta-cyanoethyl-ADP alpha S, with cyanogen bromide in aqueous solution near neutrality leads to the formation of adenosine 5'-[2-cyanoethyl diphosphate], beta-cyanoethyl-ADP, in good yield.  Reaction of Rp or Sp beta-cyanoethyl-ADP alpha S in H218O produces Sp or Rp beta-cyanoethyl-[alpha-18O]ADP, respectively, with inversion of configuration.  Removal of the cyanoethyl groups in KOH produces Sp or Rp [alpha-18O]ADP.  Desulfurization of chiral phosphorothioates by reaction with cyanogen bromide in H218O or H217O or of chiral [17O] or [18O] phosphorothioates in water appears to be a convenient method for synthesizing chiral phosphates for use in a variety of investigations of the mechanisms of enzymatic cleavage of P-O bonds.