Synthesis and in vitro biological evaluation of new P2X7R radioligands [¹¹C]halo-GSK1482160 analogs

The reference standards halo-GSK1482160 (F-, Br-, and I-) and their corresponding precursors desmethyl-halo-GSK1482160 (F-, Br-, and I-) were synthesized from (S)-1-methyl-5-oxopyrrolidine-2-carboxylic acid or (S)-5-oxopyrrolidine-2-carboxylic acid and 2-halo-3-(trifluoromethyl)benzylamine (F-, Br-, and I-) in one step with 45-93% yields. The target tracers [¹¹C]halo-GSK1482160 (F-, Br-, and I-) were prepared from desmethyl-halo-GSK1482160 (F-, Br-, and I-) with [¹¹C]CH₃OTf under basic conditions (NaOH-Na₂CO₃, solid, w/w 1:2) through N-[¹¹C]methylation and isolated by HPLC combined with SPE in 40-50% decay corrected radiochemical yield. The radiochemical purity was >99%, and the molar activity (A_M) at end of bombardment (EOB) was 370-740 GBq/μmol. The potency of halo-GSK1482160 (F-, Br-, and I-) in comparison with GSK1482160 (Cl-) was determined by a radioligand competitive binding assay using [¹¹C]GSK1482160, and the binding affinity K_i values for halo-GSK1482160 (F-, Br-, and I-) and GSK1482160 (Cl-) are 54.2, 2.5, 1.9 and 3.1 nM, respectively.