Discovery of ((S)-5-(methoxymethyl)-7-(1-methyl-1H-indol-2-yl)-2-(trifluoromethyl)-4,7-dihydropyrazolo[1,5-a]pyrimidin-6-yl)((S)-2-(3-methylisoxazol-5-yl)pyrrolidin-1-yl)methanone as a potent and selective I(Kur) inhibitor.

Previously disclosed dihydropyrazolopyrimidines are potent and selective blockers of I(Kur) current. A potential liability with this chemotype is the formation of a reactive metabolite which demonstrated covalent binding to protein in vitro. When substituted at the 2 or 3 position, this template yielded potent I(Kur) inhibitors, with selectivity over hERG which did not form reactive metabolites. Subsequent optimization for potency and PK properties lead to the discovery of ((S)-5-(methoxymethyl)-7-(1-methyl-1H-indol-2-yl)-2-(trifluoromethyl)-4,7-dihydropyrazolo[1,5-a]pyrimidin-6-yl)((S)-2-(3-methylisoxazol-5-yl)pyrrolidin-1-yl)methanone (13j), with an acceptable PK profile in preclinical species and potent efficacy in the preclinical rabbit atrial effective refractory period (AERP) model.

Dihydropyrazolopyrimidines containing benzimidazoles as K(V)1.5 potassium channel antagonists.

Dihydropyrazolopyrimidines with a C6 heterocycle substituent were found to have high potency for block of K(V)1.5. Investigation of the substitution in the benzimidazole ring and the substituent in the 5-position of the dihydropyrazolopyrimidine ring produced 31a with an IC50 for K(V)1.5 block of 0.030muM without significant block of other cardiac ion channels. This compound also showed good bioavailability in rats and robust pharmacodynamic effects in a rabbit model.