Rapid synthesis of N,N′-disubstituted piperazines. Application to the preparation of No carrier added 1-(4-[18F]fluorophenyl)piperazine and of an [18F]-selective ligand of serotoninergic receptors (5HT2antagonist)

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Abstract
An efficient and rapid method of piperazine formation (>50%, 30 min) involving the reaction of N,O,O′-tris(toluene-p-sulfonyl)bis(2-hydroxyethyl)amine 3 and 4-fluoroaniline in an alcohol or in hexamethylphosphoramide has been developed. It has been applied to the preparation of 1-(4-[18F]fluorophenyl)piperazine 6b, a new precursor in [18F]-labelling for positron emission tomography studies. Compound 6b was obtained in 7–15% decay corrected radiochemical yield in a synthesis time of 145–165 min counted from the labelled precursor [18F]fluoride and a radiochemical purity greater than 98% after HPLC purification. The utility of 6b was demonstrated by the synthesis of the [18F]naphthosultam 8b, a selective antagonist of 5-HT2 receptors. Compound 8b was obtained radiochemically pure in 50 min from 6b(including HPLC) and in an overall yield of 2.5–12%(decay corrected) from [18F]fluoride.

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