Synthesis of [2‐¹⁴C,5‐³H]cytosine and [2‐¹⁴C,5‐³H]uracil via bromination and catalytic bromine‐tritium gas exchange

Abstract

SUMMARYIn micro-scale experiments. 12-'C. 5-SHlcytosine and [2- 'C, 5-3H] uracil were synthesized via bromination and catalytic Br-'H exchange reaction with the use of [2-'4C1-cytosine and -uracil and tritium gas. The double labelling percentages of these groducts were 70 and 26, respectively. It was assumed that 12-' C,S-Br] uracil was subjected to reaction with hydrogen atom originally adsorbed on a palladium catalyst. This is to a31esser extent valid for [2-'"C,5-Br)cytosine. The percentages of H labelling at 5 position of pyrimidine ring of cytosine and uracil were proved to be 96 and 73. respectively. For the analysis and purification of products, the HPLC eluting conditions using C18 reverse column and NaHePO4 aqueous solution or HeO/methanol mixture as eluent were studied. Unreacted tritium gas was recovered with the use of adsorbents such as active charcoal and Zr-V-Fe getter.

Chemical Effects of Tritium Decay in Aqueous Solutions of Cytosine

“…[2-14 C,5-3 H]cytosine of 81% 14 C labelling, 86% Ή labelling (almost exclusively at 5 position of the pyrimidine ring) and 70% double labelling ( 14 C: 0.077 mCi, 3 H:0.038 Ci) was synthesized [11], and purified by HPLC [Column: Unisil QC 18 , particle size 5 μηι, 0 7.6 X 300mm (Gaskuro Kogyo Co. Ltd.); Mobile phase: 35% methanol aqueous solution]. The solvent in the eluate was evaporated immediately and the solid [2-14 C,5-3 H]cytosine was dissolved in water together with a large amount of non-radioactive cytosine (diluent of radioactive cytosine of high specific activity) within 1 h after the HPLC purification (15,83 or 360 times as much non-radioactive cytosine as radioactive cytosine by weight).…”

“…To minimize the detection loss of lower radioactive spots, the TLC spot of [2][3][4][5][6][7][8][9][10][11][12][13][14] 0.9 X 10 s dpm ( 14 C)) was covered with a piece of aluminum foil (> 40 mg/cm 2 ) and was exposed finally without the foil for 10 min.…”