Synthesis of [1,3-15 N2] thymine and [7-15 N] hypoxanthine

Specific 15 N-labeling of DNA fragments demonstrated its value for NMR studies of nucleic acid structure and provided unique information about nucleic acid-ligand interactions. For this purpose in the last years we prepared some purines and pyrimidines labeled with 15 N and 13 C in different positions. This paper presents 15 N-labeling of the new compounds [1,3-15 N2] thymine and [7-15 N] hypoxanthine. The 15 N labeled compounds CO(15 NH2)2 and Na15 NO2 used as starting material for labeling of thymine and hypoxanthine were obtained from H15 NO3 99 at. % 15 N produced at the National Institute for Research and Development of Isotopic and Molecular Technologies, Cluj-Napoca, Romania. The structure of labelled compounds was confirmed using mass spectrometry (MS) analysis and the isotopic label was determined by MS for the molecular compounds. (author)