Preparation of high specific-activity tritiated thymine and thymidine

A simple method was developed for the preparation of tritiated thymidine and thymine with high specific radioactivity, in which the atoms of tritium hold specific and stable positions. Thymine is labelled exclusively in the methyl group by reducing 5-chloromethyluracil with tritium. Thymidine-3H is obtained by trandeoxyribosidation between deoxy-uridine and thymine methyl-3H. The extemporaneous preparation of the catalytic deoxyribose-transferring enzyme from rat liver ensures great reproducibility to the method.
The purifications of the tritiated thymine and thymidine are effected by paper chromatography, the techniques of column chromatography being insufficiently secure at such levels of radioactivity.