Synthesis of selectively labeled histidine and its methylderivatives with deuterium, tritium, and carbon‐14

Isotopologues of l ‐histidine and its N ‐methylderivatives labeled with deuterium and tritium at the 5‐position in the imidazole ring were obtained using the isotope exchange method. The deuterium‐labeled isotopologues [5‐ 2 H]‐ l ‐histidine, [5‐ 2 H]‐ N τ ‐methyl‐ l ‐histidine, [5‐ 2 H]‐ N π ‐methyl‐ l ‐histidine, and [2,5‐ 2 H 2 ]‐ l ‐histidine were synthesized by isotope exchange method carried out in a fully deuterated medium with. The same reaction conditions were applied to synthesize [5‐ 3 H]‐ N τ ‐methyl‐ l ‐histidine, [5‐ 3 H]‐ N π ‐methyl‐ l ‐histidine, and [5‐ 3 H]‐ l ‐histidine with specific activity of 2.0, 5.0, and 2.6 MBq/mmol, respectively. The N π ‐[methyl‐ 14 C]‐histamine was obtained with specific activity of 0.23 MBq/mmol in a one‐step reaction by the direct methylation of histamine by [ 14 C]iodomethane.