Use of a ¹³C Atom to Differentiate Two ¹⁵N-Labeled Nucleosides. Syntheses of [¹⁵NH²]-Adenosine,[1,NH ₂-¹⁵N₂]- And [2-¹³C-1,NH ₂-¹⁵N₂]-Guanosine, and [1,7,NH₂- ¹⁵N₃]- and [2-¹³C-1,7,NH₂- ¹⁵N₃]-2′

We report the first examples of the specifically ¹⁵N and ¹³C multilabeled nucleosides: [1,NH₂-¹⁵N₂]-and [2-¹³C-l,NH₂-¹⁵N₂-]-guanosine; [1,7,NH₂-¹⁵N₃]- and [2-¹³C-1,7,NH₂-¹⁵N ₃]-2′-deoxyguanosine. In each set, the [¹³C] atom functions as a "tag" that allows the N1 and N2 ¹⁵N atoms of two ¹⁵N-labeled guanines to be unambiguously differentiated in RNA and DNA fragments. The syntheses employ high-yield reactions in which protecting groups are not required and use relatively low cost sources of isotopes: [¹⁵N]-ammonium chloride and [¹⁵N]- or [¹³C,¹⁵N]-potassium cyanide.