Radiosynthesis of a new radiobrominated ligand for 5HT(2A) receptors, a potential tracer for PET

4-Amino-N-[1-[3-(4-fluorophenoxy)propyl]-4-methyl-4-piperidinyl]-2-methoxy-benzamide, a compound with high affinity for 5HT(2)-receptors, was radiobrominated in the 5-position of the methoxybenzamide group by electrophilic substitution. Hydrogen peroxide / acetic acid, peracetic acid and a mixture of both were tried as oxidants. Radiobromination with the hydrogen peroxide method gave a labelling yield of 80% in the 5-position and 20% in the 3-position without any side products. On the other hand the labelling methods based on the use of peracetic acid gave a more selective radiobromination in the 5-position, but with low yields and moreover generated radioactive and non-radioactive side products. N.C.A. radiobromide of high radio-chemical purity was obtained by an ion-exchange procedure on the target material solution coupled to a purification step using methanol.