15N-Multilabeled Adenine and Guanine Nucleosides. Syntheses of [1,3,NH(2)-(15)N(3)]- and [2-(13)C-1,3,NH(2)-(15)N(3)]-Labeled Adenosine, Guanosine, 2'-Deoxyadenosine, and 2'-Deoxyguanosine.

We report a high-yield route to the following specifically (15)N- and (13)C-multilabeled nucleosides: [1,3,NH(2)-(15)N(3)]- and [2-(13)C-1,3,NH(2)-(15)N(3)]-adenosine; [1,3,NH(2)-(15)N(3)]- and [2-(13)C-1,3,NH(2)-(15)N(3)]-guanosine; [1,3,NH(2)-(15)N(3)]- and [2-(13)C-1,3,NH(2)-(15)N(3)]-2'-deoxyadenosine; [1,3,NH(2)-(15)N(3)]- and [2-(13)C-1,3,NH(2)-(15)N(3)]-2'-deoxyguanosine. In each set, the (13)C2 atom functions as a "tag" that allows the (15)N1 and (15)N3 atoms to be unambiguously differentiated from the untagged versions in (15)N NMR of RNA or DNA fragments. The key intermediate of this synthetic strategy for both the adenine and guanine nucleosides is [NH(2),CONH(2)-(15)N(2)]-5-amino-4-imidazolecarboxamide. The [2-(13)C]-label is added through a ring closure using [(13)C]-sodium ethyl xanthate (NaS(13)CSOEt). Enzymatic transglycosylation of either multilabeled 6-chloropurine or multilabeled 2-mercaptohypoxanthine and a final reaction with (15)NH(3) give the adenine and guanine nucleosides. This is the first report of a [3-(15)N]-labeled guanine nucleoside.