The syntheses of ethyl 2′-aryl-6′-(chloro, methoxy and unsubstituted)imidazo[1,2-a]pyridin-3′-yl}-2- (acylamino, acetoxy and hydroxy)acetates, 3-benzamidomethyl-2-benzoyl-6-(chloro and methoxy)imidazo-[1,2-a]pyridines, 3-amino-6-chloro-2-phenylimidazo[1,2-a]pyridine and ethyl 2-(2′-phenylimidazo[1,2-a]pyridin-3′-yl)acetate are reported. The ability of these compounds to displace [3H]diazepam from central and mitochondrial (peripheral-type) benzodiazepine receptors has been examined. Ethyl 2-benzamido-2-6′-chloro-2′-(4′′-chlorophenyl)imidazo[1,2-a]pyridin-3′-yl} acetate (21) was selective for peripheral-type receptors (IC5013 nM) but none bound strongly to central receptors.
The syntheses of some ethyl 2-2′-aryl-6′-(chloro, iodo and methoxy)imidazo[1,2-b]pyridazin-3′-yl}-2-(acetoxy, acylamino, hydroxy and methoxy)acetates, 6-methyl-2-(p-tolyl)- and 6-chloro-2-(4′-chlorophenyl)-3-trimethylammoniomethylimidazo[1,2-b]pyridazine iodides (and reactions thereof), 2-benzoyl 6-substituted imidazo[1,2-b]pyridazines and 7-(methoxy, chloro and phenylthio)-2-phenylpyrimido-[1,2-b]pyridazin-5-ium-3-olates are reported. The ability of these compounds to displace [3H]diazepam from rat forebrain membrane [central benzodiazepine receptor (BZR)] and rat kidney membrane [mitochondrial (peripheral-type) benzodiazepine receptor (PBR)] has been examined. The most active compound was ethyl 2-6′-chloro-2′-(p-tolyl)imidazo[1,2-b]pyridazin-3′-yl}-2-hydroxyacetate with IC50 24 nM for displacement from the BZR and 91% displacement at 1000 nM from the PBR; the most selective for the PBR was 6-methyl-3-methylsulfonylmethyl-2-(p-tolyl)imidazo[1,2-b]pyridazine (PBR, IC50 92 nM; BZR, 15% inhibition of binding by [3H]diazepam at 1000 nM).