2'-Amino-2'-deoxyguanosine and 3'-amino-3'-deoxyguanosine are valuable probes for investigating the metal ion interactions at the active site of the group I ribozyme. However, these experiments require a thorough understanding of the protonation state of the amino group at a specific pH. Here, we describe the first syntheses of 2'-15N-amino-2'-deoxyadenosine, 2'-15N-amino-2'-deoxyguanosine, and 3'-15N-amino-3'-deoxyguanosine. The 15N-enriched nucleus allows convenient and accurate determination of the amine pKa by 15N NMR.