title: Syntheses, calcium channel agonist-antagonist modulation activities, and voltage-clamp studies of isopropyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-pyridinylpyridine-5-carboxylate racemates and enantiomers.
abstract: A novel group of racemic isopropyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-pyridinylpyridine-5-carboxylate isomers [(+/-)-12-14] were prepared using a modified Hantzsch reaction that involved the condensation of nitroacetone with isopropyl 3-aminocrotonate and 2-, 3-, or 4-pyridinecarboxaldehyde. Determination of their in vitro calcium channel-modulating activities using guinea pig ileum longitudinal smooth muscle (GPILSM) and guinea pig left atrium (GPLA) assays showed that the 2-pyridinyl isomer (+/-)-12 acted as a dual cardioselective calcium channel agonist (GPLA)/smooth muscle selective calcium channel antagonist (GPILSM). In contrast, the 3-pyridinyl [(+/-)-13] and 4-pyridinyl [(+/-)-14] isomers acted as calcium channel agonists on both GPLA and GPILSM. The agonist effect exhibited by (+/-)-12 on GPLA was inhibited by nifedipine and partially reversed by addition of extracellular Ca2+. In anesthetized rabbits, the 4-pyridinyl isomer (+/-)-14 exhibited a hypertensive effect that was qualitatively similar to that exhibited by the nonselective agonist Bay K 8644 and the 3-pyridinyl isomer (+/)-13, whereas the 2-pyridinyl isomer (+/-)-12 induced a hypotensive effect similar to that of the calcium channel antagonist nifedipine. Similar results were obtained in a spontaneously hypertensive rat model. In vitro studies showed that the (+)-2-pyridinyl enantiomer (+)-12A exhibited agonist activity on both GPILSM and GPLA, but that the (-)-2-pyridinyl enantiomer (-)-12B exhibited agonist activity on GPLA and antagonist activity on GPILSM. Whole-cell voltage-clamp studies using isolated guinea pig ventricular myocytes indicated that (-)-12B inhibited the calcium current (ICa), that (+)-12A increased slightly ICa, and that (+/-)-12 inhibited ICa but the latter inhibition was less than that for (-)-12B. (-)-12B effectively inhibited ICa at all membrane potentials examined (-40-50 mV), whereas (+)-12A exhibited a weak agonist effect near the peak of the I-V curve. The 2-pyridinyl isomers (enantiomers) 12 represent a novel type of 1,4-dihydropyridine calcium channel modulator that could provide a potentially new approach to drug discovery targeted toward the treatment of congestive heart failure and probes to study the structure-function relationships of calcium channels.
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Vo
authors.forename: W C
authors.initials: WC
authors.lastname: Matowe
authors.forename: M
authors.initials: M
authors.lastname: Ramesh
authors.forename: N
authors.initials: N
authors.lastname: Iqbal
authors.forename: M W
authors.initials: MW
authors.lastname: Wolowyk
authors.forename: S E
authors.initials: SE
authors.lastname: Howlett
authors.forename: E E
authors.initials: EE
authors.lastname: Knaus
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002120:Calcium Channel Agonists / Q000138:chemical synthesis* / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000138:chemical synthesis* / Q000494:pharmacology*; D002264:Carboxylic Acids / Q000138:chemical synthesis* / Q000494:pharmacology*; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects; D006973:Hypertension / Q000188:drug therapy; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D009200:Myocardial Contraction / Q000187:drug effects; D009543:Nifedipine / Q000494:pharmacology; D011725:Pyridines / Q000138:chemical synthesis* / Q000494:pharmacology*; D011817:Rabbits; D051381:Rats; D011918:Rats, Inbred SHR; D012680:Sensitivity and Specificity; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
chemical_list: D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D002264:Carboxylic Acids; D011725:Pyridines; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009543:Nifedipine