Synthesis of 15 N, 13 C labelled purines

The heteronuclear NMR spectroscopy in the structural analysis of proteins and nucleic acids requires labelling with 15 N and 13 C. These NMR studies using oligonucleotides, specifically labelled with 15 N and 13 C, may provide valuable information regarding nucleic acid structure, drug binding and nucleic acid-protein interaction. For this purpose, in the last years we prepared some purines labelled with 15 N and 13 C in different positions, which were requested by Institute Pasteur from Paris, where the labelled purines will be use in enzymatic syntheses of nucleotides -15 N, 13 C. This paper presents 15 N and 13 C labelling of the following purines: [6 - 15 N] adenine; [1,3,7 - 15 N, 8 - 13 C] xanthine; [1,3,6,7 - 15 N, 8 - 13 C] adenine. The first one was obtained by amination of 6-chloropurine with 15 NH3 at high pressure and temperature. For the second one the experimental procedure is an adaptation of the synthesis method for the corresponding unlabelled compounds (the Traube method, modified by Bobransky and Synowiedsky). As starting isotopically labelled material we used CO(15 NH2)2, Na15 NO2 and H13 COOH. In the last case because of the possibility to transform purines one into another, we prepared labelled adenine in the mentioned positions, using [1,3,7 - 15 N, 8 - 13 C] xanthine as starting material. The 15 N - labelled compounds, CO(15 NH2)2, Na15 NO2 and 15 NH3, used as starting material for labelling of these purines, were obtained from H15 NO3 99 at. % 15 N, produced at the National Institute for Research and Development for Isotopic and Molecular Technologies, Cluj-Napoca, Romania. The labelled purines structure was confirmed using mass spectrometry, IR spectroscopy, NMR spectroscopy and the isotopic label was determined by mass spectrometry on the molecular compounds. (authors)