Structure-Activity Relationship Study of Subtype-Selective Positive Modulators of K(Ca)2 Channels

A series of modified N-cyclohexyl-2-(3,5-dimethyl-1H-pyrazol-1-yl)-6-methylpyrimidin-4-amine (CyPPA) analogues were synthesized by replacing the cyclohexane moiety with different 4-substituted cyclohexane rings, tyrosine analogues, or mono- and dihalophenyl rings and were subsequently studied for their potentiation of K(Ca)2 channel activity. Among the N-benzeneN-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-4-pyrimidinamine derivatives, halogen decoration at positions 2 and 5 of benzene-substituted 4-pyrimidineamine in compound 2q conferred a similar to 10-fold higher potency, while halogen substitution at positions 3 and 4 of benzene-substituted 4-pyrimidineamine in compound 2o conferred a similar to 7-fold higher potency on potentiating K(Ca)2.2a channels, compared to that of the parent template CyPPA. Both compounds retained the K(Ca)2.2a/K(Ca)2.3 subtype selectivity. Based on the initial evaluation, compounds 2o and 2q were selected for testing in an electrophysiological model of spinocerebellar ataxia type 2 (SCA2). Both compounds were able to normalize the abnormal firing of Purkinje cells in cerebellar slices from SCA2 mice, suggesting the potential therapeutic usefulness of these compounds for treating symptoms of ataxia.