Synthesis of tritium-labeled immunodepressants containing double bonds by isotope exchange with tritium water

Conditions for tritium labeling of Cyclosporin A (1) (C<INF>62</INF>H<INF>1 11</INF>N<INF>11</INF>O<INF>12</INF>) and FK-506 {17-allyl-1,14-dihydroxy-1 2-[2-(4-hydroxy-3-methoxycyclohexyl)-1-methylvinyl-23,25-dimethoxy-13,19,21 ,27-tetramethyl-11,28-dioxa-4-azatricyclo[22.3.1.0<SUP>4,9</SUP>]octacos-1, 8-ene-2,3,10,16-tetraone} (2) (C<INF>44</INF>H<INF>69</INF>NO<INF>12</INF>) were determined. Under the conditions of liquid-phase and solid-phase meth ods the unsaturated fragments of 1 and 2 were virtually completely reduced. Only isotope exchange with tritium water yielded tritium-labeled compounds 1 and 2 with molar radioactivities of 4 and 16 Ci mmol<SUP>-1</SUP>, respe ctively.