A series of 6-alkylthio- and 6-arylthio-3-methoxy-2-phenylimidazo[l,2- b]pyridazines has been prepared from 6-alkylthio-and 6-arylthio-pyridazin-3-amines through the corresponding 6-alkylthio-and 6-arylthio-2-phenylimidazo[l,2-b] pyridazin-3(5H)-ones.
Some 6-arylthio( aryloxy and alkylthio )-3-( acetamidomethyl , benzamidomethyl, methoxy and unsubstituted )-2-arylimidazo[1,2-b] pyridazines have been prepared and examined for their ability to displace [3H]diazepam from rat brain membranes. The most active compound was 3-acetamidomethyl-2-(3',4'-methylenedioxyphenyl)-6-phenylthioimidazo[1,2-b] pyridazine with IC50 4.4 nM. The 3-acylaminomethyl-6-(2- and 3-methoxyphenylthio)-2-phenylimidazo[1,2-b] pyridazines proved less active than their 6-phenylthio analogues, and larger substituents at the 2- and 6-positions markedly decreased binding. Significant differences in binding ability have been observed between 3-acylaminomethyl-2-aryl-6-phenylthioimidazo[1,2-b] pyridazines and the corresponding imidazo [1,2-a]pyridines.
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.