Use of a 13C Atom To Differentiate Two 15N-Labeled Nucleosides. Syntheses of [15NH2]-Adenosine, [1,NH2-15N2]- and [2-13C-1,NH2-15N2]-Guanosine, and [1,7,NH2-15N3]- and [2-13C-1,7,NH2-15N3]-2‘-Deoxyguanosine

We report the first examples of the specifically 15 N and 13 C multilabeled nucleosides: [1,NH 2 - 15 N 2 ]-and [2- 13 C-1,NH 2 - 15 N 2 -]-guanosine; [1,7,NH 2 - 15 N 3 ]- and [2- 13 C-1,7,NH 2 - 15 N 3 ]-2‘-deoxyguanosine. In each set, the [ 13 C] atom functions as a “tag” that allows the N1 and N2 15 N atoms of two 15 N-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: [ 15 N]-ammonium chloride and [ 15 N]- or [ 13 C, 15 N]-potassium cyanide.