Syntheses of selenium labelled compounds--II. The exchange reaction with elemental selenium

73Se labelled 2-selenouracil was prepared by the isotope exchange reaction method. It has been well known that in order to prepare labelled compounds in high specific activity by exchange reaction, the substrate compounds have to be used in small quantities. For 2-selenouracil, however, the reaction in low concentration is not always preferable for the labelling of high specific activity within a limited time. The optimum conditions for the preparation of [2-73Se]-2-selenouracil of maximum specific activity were determined.