Isotope exchange reactions of trans-zeatin with tritium

Isotope exchange of trans-zeatin with high-activity tritium water and with gaseous tritium in solution, and also the solid-phase catalytic hydrogenation of this compound were studied. The isotope exchange of trans-zeatin with gaseous tritium, both in solution and without a solvent at 160°C and higher temperatures, is accompanied by virtually complete hydrogenation of the starting compound with the formation of tritium-labeled dihydrozeatin. The isotope exchange of trans-zeatin with high-activity tritium water allows preparation of tritium-labeled zeatin in 67% yield and molar activity of 0.68 PBq mol^?1. When the solid-phase isotope exchange is performed at 150–155°C, the reaction products contain tritium-labeled trans-zeatin along with the hydrogenation product, dihydrozeatin. At 170°C, the only reaction product is dihydrozeatin. Thus, the selectivity of tritium labeling varies with the temperature of solid-phase catalytic hydrogenation. Below 160°C, the solid-phase reaction can be performed selectively, i.e., with the preservation of the double bond in the starting trans-zeatin. Above 170°C, the selectivity is lost, and the compound is virtually fully hydrogenated to dihydrozeatin.