SYNTHESES OF [6,7-N-15]-ADENOSINE, [6,7-N-15]-2'-DEOXYADENOSINE, AND [7-N-15]-HYPOXANTHINE

We have developed a high-yield route for the synthesis of [7-N-15]-hyp oxanthine in four steps in an overall yield of 81%. This procedure use s [N-15]-sodium nitrite as the N-15 source and an inexpensive pyrimidi ne to provide an economical route to this useful N-15-labeled intermed iate. Conversion to [7-N-15]-6-chloropurine followed by enzymatic tran sglycosylation gives the corresponding ribo- and 2'-deoxyribonucleosid es. Ammonolysis of the 6-chloro moiety to give the [6,7-N-15]-labeled nucleosides is effected simply and in high yield using 2 equiv of [N-1 5]-ammonium chloride and 3 equiv of potassium bicarbonate.