18O Labeled Nucleosides. 2. A General Method for the Synthesis of Specifically Labeled Pyrimidine Ribonucleosides1

A facile method for the synthesis of highly enriched 18O labeled pyrimidine ribonucleosides is described using uridine as a model compound. The isotopic label may be selectively incorporated into the base moiety at O2 or into the ribose portion of the molecule at the 5′ position. In addition, both positions may be labeled and this is the first report of a method for labeling of both the base and sugar moieties of pyrimidine ribonucleosides. The site and level of isotope incorporation may be determined mass spectrometrically.