USE OF A C-13 ATOM TO DIFFERENTIATE 2 N-15-LABELED NUCLEOSIDES - SYNTHESES OF [(NH2)-N-15]-ADENOSINE, [1,NH2-N-15(2)]-GUANOSINE AND [2-C-13-1,NH2-N-15(2)]-GUANOSINE, AND [1,7,NH2-N-15(3)]-DEOXYGUANOSINE AND [2-C-13-1,7,NH2-N-15(3)]-2'-DEOXYGUANOSINE

We report the first examples of the specifically N-15 and C-13 multila beled nucleosides: [1,NH2-N-15(2)]- and [2-C-13-1,NH2-N-15(2)-]-guanos ine; [1,7,NH2-N-15(3)]- and [2-C-13-1,7,NH2-N-15(3)]-2'-deoxyguanosine . In each set, the [C-13] atom functions as a ''tag'' that allows the N1 and N2 N-15 atoms of two N-15-labeled guanines to be unambiguously differentiated in RNA and DNA fragments. The syntheses employ high-yie ld reactions in which protecting groups are not required and use relat ively low cost sources of isotopes: [N-15]-ammonium chloride and [N-15 ]- Or [C-13,N-15]-potassium cyanide.