Synthesis of substituted [I-123]imidazo[1,2-alpha]pyridines as potential probes for the study of the peripheral benzodiazepine receptors using SPECT

The imidazo[1,2-a]pyridines [N,N'-dimethyl-6-chloro-(4'-iodophenyl)imidazo[ 1,2-a]pyridine-3-acetamide 1, [N,N'-diethyl-6-chloro-(4'-iodophenyl)imidazo [1,2-a]pyridine-3-acetamide 2, and [N-methyl-6-chloro-(4'-iodophenyl)imidaz o[1,2-a]pyridine-3-acetamide 3, are high affinity and selective ligands for the Peripheral Benzodiazepine Receptors (PBR). The [I-123]1-3 labelled ana logues of these compounds were subsequently synthesised for the potential s tudy of the PBR in vivo using SPECT. Radioiodination was achieved by iodode stannylation reactions of the corresponding tributyl tin precursors with Na [I-123] in the presence of peracetic acid, chloramine-T or Iodogen. Purific ation of the crude product was achieved by semipreparative C-18 RP HPLC to give the products in radiochemical yields of 40-85%. The products were obta ined in >97% chemical and radiochemical purity and with specific activities > 80 GBq/mu mol.