Radiosynthesis of a 11C-labelled benzodiazepine receptor agonist: 1-[11C]alprazolam

The benzodiazepine receptor agonist, alprazolam (3) has been successfully labelled with carbon-11 in a metabolically stable position. Reaction of the amidrazone, 7-chloro-5-phenyl-3H-1,4-benzodiazepine-2-yl hydrazine (1), with l-[11C]acetyl chloride followed by pyrolysis of the resulting 1-acetyl-hydrazine 2 afforded the title compound 1-[11C]alprazolam in 43-65% yield, in 40-55 min at specific activities of 0.93-2.18 Ci/μmol. The straightforward synthesis herein reported lends itself well to a useful remote controlled synthesis. (author)