Imidazo[1,2-b]Pyridazines. XXI. Syntheses of Some 3-Acylaminomethyl-6-(chloro, fluoro, methoxy, methylthio, phenoxy and phenylthio)-2-(phenyl, 4-t-butylphenyl, 4-cyclohexylphenyl, β-naphthyl and styryl)imidazo[1,2-b]pyridazines and Their Interaction With Central and Peripheral-Type Benzodiazepine Receptors

Some 3-(aliphatic and aromatic) acylaminomethyl derivatives of 6-( chloro, fluoro, methoxy, methylthio, phenoxy and phenylthio )-2-(phenyl, 4-t-butylphenyl, 4-cyclohexylphenyl, β- naphthyl and styryl ) imidazo [1,2-b] pyridazines have been prepared and tested for binding to central benzodiazepine receptors present in rat brain membrane, and to peripheral-type (mitochondrial) benzodiazepine receptors present in rat kidney membrane. Some of these compounds which contained 2-(4-t-butylphenyl, 4-cyclohexylphenyl and styryl ) substituents bound strongly and selectively to peripheral-type benzodiazepine receptors. For example, 2-(4′-t-butylphenyl)-6-chloro-2-(4″-fluorobenzamidomethyl) imidazo [1,2-b] pyridazine in tests for the displacement of [3H]diazepam from both peripheral-type and central benzodiazepine receptors gave IC50 <1.0 nM and 9% displacement at 1000 nM , respectively. Steric effects appeared to be more restrictive in the interaction of these ligands with central benzodiazepine receptors rather than with peripheral-type benzodiazepine receptors; X-ray structure analyses of two typical compounds are reported.