Deuterium Labeling of Dopaquine

The possibility of introducing deuterium into dopaquine, a compound consisting of quinone and dopamine fragments, was examined. The isotope exchange can be carried out with deuterated water in the presence of trifluoroacetic acid (TFA) and HCl. The best results were obtained with TFA at 80°С. To activate isotope exchange, catalysts based on iridium or palladium (5% Pd/Al₂O₃, cycloocta-1,5-dienyliridium(I) 1,1,1,5,5,5-hexafluoropentane-2,4-dionate) were added to the reaction mixture in addition to the acid component. The preparative synthesis of [D]dopaquine was carried out by isotope exchange with deuterated water (D₂O : TFA 5 : 1, 80°С, 3 h). [D]Dopaquine was obtained in 20% yield with the deuterium content in the interval 1.2–1.4 atoms per molecule. The deuterium content in the dopamine fragment is 1.2–1.3 atoms per molecule. The quinone fragment contained approximately 4–7% of the isotope.