Synthesis and biological evaluation of 1,4-dihydropyridine calcium channel modulators having a diazen-1-ium-1,2-diolate nitric oxide donor moiety for the potential treatment of congestive heart failure Original Research Article

A group of racemic 4-aryl(heteroaryl)-1,4-dihydro-2,6-dimethyl-3-nitropyridines possessing nitric oxide donor O2-acetoxymethyl-1-(N-ethyl-N-methylamino, or 4-ethylpiperazin-1-yl)diazen-1-ium-1,2-diolate, C-5 ester substituents were synthesized by coupling the respective 4-aryl(heteroaryl)-1,4-dihydro-2,6-dimethyl-3-nitropyridine-5-carboxylic acids with either O2-acetoxymethyl-1-[N-(2-methylsulfonyloxyethyl)-N-methylamino]diazen-1-ium-1,2-diolate, or O2-acetoxymethyl-1-[4-(2-methylsulfonyloxyethyl)piperazin-1-yl]diazen-1-ium-1,2-diolate. Compounds having a C-4 2-pyridyl, 4-pyridyl, 2-trifluoromethylphenyl, or benzofurazan-4-yl substituent exhibited more potent smooth muscle calcium channel antagonist activity (IC50ʹs in the 0.37–1.09 μM range) than related analogs having a C-4 3-pyridyl substituent (IC50ʹs=3.03–9.14 μM range) relative to the reference drug nifedipine (IC50=9.13 nM). The point of attachment of C-4 isomeric pyridyl substituents was a determinant of smooth muscle calcium channel antagonist activity where the relative potency profile was 4-pyridyl>2-pyridyl>3-pyridyl. Replacement of the C-5 methyl ester substituent of methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)pyridine-5-carboxylate (Bay K 8644) by an O2-acetoxymethyl-1-(N-ethyl-N-methylamino)diazen-1-ium-1,2-diolate, or O2-acetoxymethyl-1-(4-ethylpiperazin-1-yl)diazen-1-ium-1,2-diolate, C-5 ester substituent provided compounds, which exhibited a lower, yet respectable, cardiac positive inotropic effect (IC50ʹs=4.82 and 4.05 μM, respectively) relative to the reference drug Bay K 8644 (IC50=0.30 μM). All compounds released nitric oxide upon incubation with either phosphate buffer at pH 7, or porcine liver esterase. However, the percentage nitric oxide released was up to 3-fold higher (76%) when these O2-acetoxymethyl-1-(alkylamino)diazen-1-ium-1,2-diolates were incubated with guinea pig serum. These results suggest that radical dotNO would be released in vivo, upon cleavage by nonspecific serum esterases, preferentially in the vascular endothelium where it may enhance smooth muscle calcium channel antagonist activity.