Synthesis of pentamidine labelled with tritium and carbon‐14

Tritium labelled pentamidine has been prepared with a specific activity of 90 mCi mmol−1 using a one-step exchange reaction between the unlabelled drug and tritiated water. The labelling utilised a homogeneous rhodium trichloride catalyst and yielded pentamidine regiospecifically labelled in the positions ortho to the amidine groups. Carbon-14 labelled pentamidine was prepared via a seven-step procedure in which the isotope was introduced via a nucleophilic substitution of 4-bromo-phenol with copper(I) [14C]cyanide.