Synthesis and biological evaluation of 18F labeled fluoro-oligo-ethoxylated 4-benzylpiperazine derivatives for sigma-1 receptor imaging


Synthesis and biological evaluation of 18F labeled fluoro-oligo-ethoxylated 4-benzylpiperazine derivatives for sigma-1 receptor imaging

Wang, X.; Li, Y.; Deuther-Conrad, W.; Xie, F.; Chen, X.; Cui, M.-C.; Zhang, X.-J.; Zhang, J.-M.; Steinbach, J.; Brust, P.; Liu, B.-L.; Jia, H.-M.

We report the synthesis and evaluation of a series of fluoro-oligo-ethoxylated 4-benzylpiperazine derivatives as potential σ1 receptor ligands. In vitro competition binding assays showed that 1-(1,3-benzodioxol-5-ylmethyl)-4-(4-(2-fluoroethoxy)benzyl)piperazine (6) exhibits low nanomolar affinity for σ1 receptors (Ki = 1.85 ± 1.59 nM) and high subtype selectivity (σ2 receptor: Ki = 291 ± 111 nM ; Kiσ2/Kiσ1 = 157). [18F]6 was prepared in 30–50% isolated radiochemical yield, with radiochemical purity of >99% by HPLC analysis after purification, via nucleophilic 18Fˉ substitution of the corresponding tosylated precursor. The log DpH7.4 value of [18F]6 was found to be 2.57 ± 0.10, which is within the range expected to give high brain uptake. Biodistribution studies in mice demonstrated relatively high concentration of radiotracers in organs known to contain σ1 receptors, including the brain, lungs, kidneys, heart, and spleen. Administration ofhaloperidol 5 min prior to injection of [18F]6 significantly reduced the concentration of radiotracer in the above-mentioned organs. The accumulation of radiotracers in the bone was quite low suggesting that [18F]6 is relatively stable to in vivo defluorination.
The ex vivo autoradiography in rat brain showed high accumulation of radiotracer in the brain areas known to possess high expression of σ1 receptors. These findings suggest that [18F]6 is a suitable radiotracer for imaging σ1 receptors with PET in vivo.

Keywords: σ1 receptor; fluoro-oligo-ethoxylated; 4-benzylpiperazine; F-18

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Publ.-Id: 17992