Use of 2-[(18)F]fluoroethylazide for the Staudinger ligation - Preparation and characterisation of GABA(A) receptor binding 4-quinolones.

The labelling reagent 2-[(18)F]fluoroethylazide was used in a traceless Staudinger ligation. This reaction was employed to obtain the GABA(A) receptor binding 6-benzyl-4-oxo-1,4-dihydro-quinoline-3-carboxylic acid (2-[(18)F]fluoroethyl) amide. The radiotracer was prepared with a non-decay corrected radiochemical yield of 7%, a radiochemical purity >95% and a specific radioactivity of 0.9 GBq/micromol. The compound showed low brain penetration in normal rats. A series of fluoroalkyl 4-quinolone analogues with nanomolar to sub-nanomolar affinity for the GABA(A) receptor has been prepared as well.