Nucleoside uptake by red blood cells from a primitive vertebrate, the Pacific hagfish (Eptatretus stouti), is mediated by a nitrobenzylthioinosine-insensitive transport system.

Red blood cells from the Pacific hagfish (Eptatretus stouti) were found to possess a facilitated diffusion nucleoside transport system insensitive to inhibition by the nucleoside transport inhibitor nitrobenzylthioinosine (NBMPR). Uridine uptake by this route was saturable (apparent Km 0.14 mM; Vmax 2 mmol/l cells per h at 10 degrees C), inhibited by inosine and adenosine, and blocked both by the vasodilator dipyridamole and by the thiol-reactive agent p-chloromercuriphenylsulphonate. The properties of this carrier resemble closely those of NBMPR-insensitive nucleoside transport systems in some mammalian neoplastic cell lines and in rat red cells. The presence of this type of carrier in a primitive vertebrate suggests that such transporters have a broad biological distribution and that they pre-date or arose at an early stage of vertebrate evolution.

Characterization of normal, glutathione-deficient and arginase-deficient sheep erythrocytes by 1H-NMR spectroscopy.

Normal sheep erythrocytes as well as glutathione- (GSH-) deficient and arginase-deficient sheep erythrocytes have been characterized by 1H nuclear magnetic resonance spectroscopy. The GSH deficiency is a result of defective amino acid transport (lesion 1), diminished gamma-glutamylcysteine synthetase activity (lesion 2), or both (lesions (1 + 2)). 1H-NMR spectra of normal sheep erythrocytes are similar to those for human erythrocytes, and consist of resonances from a number of small intracellular molecules, including GSH. In contrast, the resonances for GSH in the GSH-deficient erythrocytes are much weaker, and strong resonances are observed for lysine, threonine and ornithine or arginine, depending on the arginase activity, in erythrocytes with lesion 1 and lesions (1 + 2). A comparison of the intensity of GSH resonances in spectra for normal and GSH-deficient erythrocytes with GSH levels determined spectrophotometrically following reaction with the nonspecific thiol reagent 5,5'-dithiobis(2-nitrobenzoate) (DTNB) indicates that either not all of the GSH determined with Ellman's reagent is free and observable by 1H-NMR or that not all of the thiol determined by Ellman's reagent is GSH. If the latter is the case, the GSH levels determined with Ellman's reagent for erythrocytes with lesions (1 + 2) are most affected, which might account for their high susceptibility to oxidative stress.

Synthesis and calcium channel antagonist activity of dialkyl 4- (dihydropyridinyl)-1,4-dihydro-2,6-dimethyl-3,5-pyridinecarboxylates.

The sodium borohydride reduction of 3,5-disubstituted 1,4-dihydro-2,6-dimethyl-4-(pyridinyl)pyridines 2 and 5 in the presence of methyl, phenyl, or tert-butyl chloroformate afforded the respective 4-(dihydropyridinyl)-1,4-dihydropyridines 4 and 6 in good yield. Products 4 comprised a mixture of the 1,2- and 1,6-dihydropyridinyl regioisomers 4a and 4b where 4a was always the predominant regioisomer. Compounds possessing a 4-[dihydro-1-(phenoxycarbonyl)-3-pyridinyl] substituent, such as 26, were also a mixture of two regioisomers 26a and 26b, and each regioisomer existed as a mixture of two rotamers in Me2SO-d6 at 25 degrees C (26a', 26a'', and 26b', 26b'') due to restricted rotation about the nitrogen-to-carbonyl carbamate bond. The calcium antagonist activities for 4 and 6 were determined by using the muscarinic receptor-mediated Ca2+-dependent contraction of guinea pig ileal longitudinal smooth muscle. The relative order of activities for the 4-(dihydropyridinyl) analogues was 4-(dihydro-3-pyridinyl) greater than 4-(dihydro-4-pyridinyl). Increasing the size of the C-3(5) alkyl ester substituents increased activity. Compounds having nonidentical ester substituents were more active than those having identical ester substituents. Replacement of the C-3 and/or C-5 ester substituents by a cyano substituent(s) decreased activity significantly. An approximate 1:1 correlation between the IC50 value for inhibition of [3H]nitrendipine binding and inhibition of the tonic component of the muscarinic-induced contractile response was observed. The test results suggest that a 4-(dihydropyridinyl) substituent is bioisosteric with a 4-(nitrophenyl) substituent on a 1,4-dihydropyridine ring where m- and p-nitrophenyl are bioisosteric with the 4-[1,2(1,6)-dihydro-3-pyridinyl] 4 and 4-(1,2-dihydro-4-pyridinyl) 6 isomers, respectively.

Synthesis and calcium channel antagonist activity of dialkyl 1,4-dihydro-2,6-dimethyl-4-(pyridinyl)-3,5-pyridinedicarboxylates.

The Hantzsch condensation of alkyl acetoacetates 3 with methyl 3-aminocrotonate (4) and pyridinecarboxaldehydes 5 afforded the unsymmetrical alkyl methyl 1,4-dihydro-2,6-dimethyl-4-(pyridinyl)-3,5-pyridinedicarboxylates 6, whereas condensation of 3 with 5 and ammonium hydroxide gave the symmetrical dialkyl 1,4-dihydro-2,6-dimethyl-4-(pyridinyl)-3,5-pyridinedicarboxylates 7. The calcium channel antagonist activities of disubstituted 1,4-dihydro-3,5-pyridinedicarboxylates 6,7, and 9 were determined with use of the muscarinic-receptor-mediated Ca2+-dependent contraction of guinea pig ileal longitudinal smooth muscle. The relative potency order for isomeric pyridinyl analogues 6 and 7 was 2-pyridinyl greater than 3-pyridinyl greater than 4-pyridinyl. Increasing the size of the alkyl ester substituents enhanced activity. Compounds having nonidentical ester substituents were more potent than those having identical ester substituents. Replacement of the C-3 and/or C-5 ester substituent(s) by a cyano substituent(s) decreased activity significantly. An approximate 1:1 correlation between the IC50 value for inhibition of [3H]nitrendipine binding and inhibition of the tonic component of the muscarinic-induced contractile response was observed. The test results suggest that a 4-(pyridinyl) substituent is bioisosteric with a 4-(nitrophenyl) substituent on a 1,4-dihydropyridine ring system where o-, m-, and p-nitrophenyl are bioisosteric with 2-pyridinyl, 3-pyridinyl, and 4-pyridinyl, respectively.

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.

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.

Synthesis and calcium channel-modulating effects of alkyl (or cycloalkyl) 1,4-dihydro-2,6-dimethyl-3-nitro-4-pyridyl-5-pyridinecarboxylate racemates and enantiomers.

A group of racemic alkyl (or cycloalkyl) 1,4-dihydro-2,6- dimethyl-3-nitro-4-(2-, 3-, or 4-pyridyl)-5-pyridinecarboxylate isomers (6-14) were prepared using a modified Hantzsch reaction that involved the condensation of nitroacetone with an alkyl (or cycloalkyl) 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-pyridyl isomers acted as dual cardioselective calcium channel agonists (GPLA)/smooth muscle selective calcium channel antagonists (GPILSM). In contrast, the 3-pyridyl and 4-pyridyl isomers acted as calcium channel agonists on both GPLA and GPILSM. In the C-4 2-pyridyl group of compounds, the size of the C-5 alkyl (or cycloalkyl) ester substituent was a determinant of GPILSM antagonist activity where the relative activity profile was cyclopentyl and cyclohexyl > t-Bu, i-Bu, and Et > MeOCH2CH2 > Me. The point of attachment of the C-4 pyridyl substituent was a determinant of GPLA agonist activity where the potency order was generally 4- and 3-pyridyl > 2-pyridyl. (+)-Cyclohexyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-pyridyl)-5- pyridinecarboxylate [(+)-14a] was a less potent calcium antagonist (IC50 = 5.27 x 10(-6) M) than the (-)-enantiomer (IC50 = 7.48 x 10(-8) M) on GPILSM. In the GPLA assay, (+)-14a exhibited a much more potent agonist effect (EC50 = 8.45 x 10(-6) M) relative to the marginal agonist effect produced by (-)-14a. The C-4 2-pyridyl compounds (enantiomers) constitute a novel type of 1,4-dihydropyridine calcium channel modulator that could provide a new drug design concept directed toward the treatment of congestive heart failure, and for use as probes to study the structure-function relationships of calcium channels.

Synthesis, rotamer orientation, and calcium channel modulation activities of alkyl and 2-phenethyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(3- or 6-substituted-2-pyridyl)-5-pyridinecarboxylates.

A group of racemic alkyl and 2-phenethyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(3- or 6-substituted-2-pyridyl)-5-pyridinecarboxylates (13a-q) was prepared using a modified Hantzsch reaction that involved the condensation of a 3- or 6-substituted-2-pyridinecarboxaldehyde (7a-j) with an alkyl or 2-phenethyl 3-aminocrotonate (11a-d) and nitroacetone (12). Nuclear Overhauser (NOE) studies indicated there is a significant rotamer fraction in solution where the pyridyl nitrogen is oriented above the 1,4-dihydropyridine ring, irrespective of whether a substituent is located at the 3- or 6-position. A potential H-bonding interaction between the pyridyl nitrogen free electron pair and the suitably positioned 1,4-dihydropyridine NH moiety may stablize this rotamer orientation. In vitro calcium channel antagonist and agonist activities were determined using guinea pig ileum longitudinal smooth muscle (GPILSM) and guinea pig left atrium (GPLA) assays, respectively. Compounds having an i-Pr ester substituent acted as dual cardioselective calcium channel agonists (GPLA)/smooth muscle-selective calcium channel antagonists (GPILSM), except for the C-4 3-nitro-2-pyridyl compound which exhibited an antagonist effect on both GPLA and GPILSM. In contrast, the compounds with a phenethyl ester group, which exhibited antagonist activity (IC50 = 10(-5)-10(-7) M range) on GPILSM, were devoid of cardiac agonist activity on GPLA. Structure-activity relationships showing the effect of a substituent (Me, CF3, Cl, NO2, Ph) at the 3- or 6-position of a C-4 2-pyridyl moiety and a variety of ester substituents (Me, Et, i-Pr, PhCH2CH2-) upon calcium channel modulation are described. Compounds possessing a 3- or 6-substituted-2-pyridyl moiety, in conjuction with an i-Pr ester substituent, are novel 1,4-dihydropyridine calcium channel modulators that offer a new drug design approach directed to the treatment of congestive heart failure and may also be useful as probes to study the structure-function relationships of calcium channels.

Specific inhibition of Ca-activated K channels in red cells by selected dihydropyridine derivatives.

1. Thirty two dihydropyridine derivatives were screened as potential inhibitors of the Ca-activated K-channel in human red cells. 2. Three derivatives (26, 29, 32 see Tables 1 and 2) with high activity were then characterized in detail, and also tested against the smooth muscle Ca-channel and shown to have varying potencies. 3. One of the more potent derivatives (32) and nitrendipine were also tested on the Ca-activated K-channel, Maxi-K channel, from mouse pancreatic beta-cells. 4. We conclude from our results that it may be possible to develop selective Gardos-channel inhibitors based on these molecules, which may be of benefit in the treatment of sickle cell disease.

A simple method for processing erythrocytes for scanning electron microscopy.

A simple method for preparing erythrocytes for scanning electron microscopy by sequential fixation with glutaraldehyde and dehydration in a graded series of alcohols is presented. The method will allow visualization of membrane defects not seen under the light microscope and is therefore suitable for routine processing of erythrocytes for diagnosis of pathologic states.

Evidence for bumetanide-sensitive, Na(+)-dependent, partial Na-K-Cl co-transport in red blood cells of a primitive fish.

Tracer uptake studies identified the major routes for K+ transport in hagfish red cells, resolving them into ouabain-sensitive, loop diuretic-sensitive, and residual components. The K1/2 values for ouabain, bumetanide, and furosemide were 10(-5), 6 x 10(-7), and 5 x 10(-6) M, respectively. The properties of the Na-K-Cl co-transporter were investigated further by varying K+, Na+, and Cl- concentrations. The measured K1/2 values were similar to those for human red cells. Finally, the stoichiometry of Na:K:Cl uptake was determined, giving 1:1 for K+:Cl-; in contrast, no significant Na+ flux could be measured, although Na+ content must be present for measurable bumetanide-dependent K+ or Cl- flux to occur. The Na-K-Cl transport therefore shows Na(+)-dependent KCl co-transport or partial flux of the system.

Hypertension: cation transport and the physical properties of erythrocytes.

In recent years, many reports have appeared describing altered Na+ and K+ transport in erythrocytes of individuals with essential hypertension. Collectively, the interpretation of these results has been unclear. Our studies revealed that the active ouabain-sensitive K+ influx, the furosemide-sensitive K+ influx and the residual passive K+ influx in both human and rat erythrocytes can vary considerably among individual persons or rats and that these measurements alone can not be used to distinguish normotensive from hypertensive individuals. The only consistent cation transport difference observed was an increased Na+ permeability in spontaneously hypertensive rat (SHR) erythrocytes. We have also examined certain physical properties (equilibrium density distribution and sedimentation velocity) of erythrocytes from normotensive Wistar-Kyoto (WKY) and SHR rats, since these characteristics may be altered in response to abnormalities of ion transport. It was found that the erythrocytes from geographically, environmentally, and age-matched littermates of WKY and SHR rats have identical equilibrium density distributions. It was also found that the density distribution of erythrocytes can vary among geographically dispersed colonies of the same strain of rat, and even among successive litters of the same rat colony. However, the sedimentation time required for erythrocytes to reach their equilibrium density was always shorter in the normotensive WKY samples than in the matched SHR. Utilizing a simple centrifugation method, we were able to clearly show that for any population of erythrocytes with the same upper limit of cell density, normotensive WKY cells always sediment at a faster rate than those of the hypertensive SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

Scanning electron microscopy of blood cells.

Scanning electron microscopy (SEM) is an invaluable tool for studying the surface morphology of isolated blood cells. We have used a simple preparative technique for SEM to study the erythrocytes from a case of Congenital Dyserythropoietic Anaemia type II and the leucocytes from healthy individuals or patients with leukaemia or lymphoma. This rapid and inexpensive technique for fixation and dehydration of blood cells was found to be equally reliable for obtaining micrographs of healthy or diseased leucocytes or erythrocytes.

Localization of cation interactions in the smooth muscle of the guinea-pig taenia coli.

1. An electron microscopic method has been developed and used to study cation binding sites in smooth muscle.2. Uranyl cations normally bind to the external surface of the plasma membrane. However, uranyl also binds to the inner surface when it is accessible. Similar binding has been observed in skeletal muscle, nerve and red blood cells.3. Uranyl binds electrostatically, and the binding can be competitively reversed by other cations. By a quantitative procedure the relative affinities Ca(2+) approximately Mg(2+) >> K(+) > Na(+) for the membrane sites have been determined. This sequence is in agreement with previous values determined analytically.4. The results support a counter-cation hypothesis for the plasma membrane surfaces of the taenia coli, and may explain features of the electrical activity in smooth muscle.

Changes in the cation composition and active K+ transport in the red cells of fetal sheep prepartum.

The red blood cells of lambs, genotypically low potassium type, undergo a transition from high potassium to low potassium cell type from parturition onwards. This involves gradual changes in cell ion content, sodium pump activity, and ouabain binding. In the present study we investigated the properties of fetal red blood cells from 30 days prepartum using the chronically cannulated pregnant ewe preparation. We demonstrate that intracellular sodium increases and potassium decreases from -30 days onwards. Sodium pump activity monitored either by tracer potassium influx or ouabain binding is markedly higher in the early fetal samples examined and declines fourfold during the final month in utero. Unlike the maternal low potassium cells the early fetal red cells are refractory in terms of sodium pump stimulation by anti-L, the antibody in fact consistently inhibiting the pump. Finally, we have investigated the volume sensitivity and development of the ouabain-insensitive potassium fluxes in these cells and found that both fetal and maternal cells show a marked chloride-dependent, volume-sensitive passive potassium flux. We conclude that the decrease in active sodium transport between fetal red cells and adult low potassium cells is achieved partly by a reduction in the density of sodium pumps per cell, and then later by the introduction into the circulation of cells with Lp-antigen-modified sodium pumps.

Synthesis and beta-adrenergic antagonist activity of heterocyclic propanolamines.

The synthesis and beta-adrenergic antagonist activities of a group of 1-(heteroaryloxy)- and 1-(heteroaryl)-3-alkylamino-2-propanols is described. beta 1-Adrenolytic (atria) structure-activity correlations indicated that replacement of the 1-naphthyl moiety of propranolol by a 4-quinolyl- (10), 2-quinolyl- (24), or 2-pyrimidyl- (26) heterocyclic moiety resulted in a 10-16 fold reduction in activity. The 1-(4-quinolyloxy)- (10) and 1-(2-quinolyloxy)- (24-25) heteroaryl moieties provided more potent activity than the structurally related 1-[2-(2H-isoquinolin-1-one)]- (31-32) or 1-[3-(3H-quinazolin-4-one)]- (35-36) moieties. All compounds tested exhibited weak beta 2-adrenolytic activity on trachea. Although the most potent beta 1-antagonist, 1-(2-pyrimidyloxy)-3-isopropylamino-2-propanol (26), was 13-fold less potent than metoprolol, it exhibited a beta 1/beta 2 selectivity ratio superior to the cardioselective metoprolol.

Volume-sensitive taurine transport in fish erythrocytes.

Taurine plays an important role in cell volume regulation in both vertebrates and invertebrates. Erythrocytes from two euryhaline fish species, the eel (Anguilla japonica) and the starry flounder (Platichthys stellatus) were found to contain high intracellular concentrations of this amino acid (approximately equal to 30 mmol per liter of cell water). Kinetic studies established that the cells possessed a saturable high-affinity Na+-dependent beta-amino-acid transport system which also required Cl- for activity (apparent Km (taurine) 75 and 80 microM; Vmax 0.85 and 0.29 mumol/g Hb per hr for eel (20 degrees C) and flounder cells (10 degrees C), respectively. This beta-system operated with an apparent Na+/Cl-/taurine coupling ratio of 2:1:1. A reduction in extracellular osmolarity, leading to an increase in cell volume, reversibly decreased the activity of the transporter. In contrast, low medium osmolarity stimulated the activity of a Na+-independent nonsaturable transport route selective for taurine, gamma-amino-n-butyric acid and small neutral amino acids, producing a net efflux of taurine from the cells. Neither component of taurine transport was detected in human erythrocytes. It is suggested that these functionally distinct transport routes participate in the osmotic regulation of intracellular taurine levels and hence contribute to the homeostatic regulation of cell volume. Volume-induced increases in Na+-independent taurine transport activity were suppressed by noradrenaline and 8-bromoadenosine-3', 5'-cyclic monophosphate, but unaffected by the anticalmodulin drug, pimozide.

Synthesis and beta-adrenergic antagonist activity of novel (3-oxazolinyl-1,4-dihydropyridyl) propanolamines.

A novel class of 1-(1-[4-phenyl(n-butyl or methyl)-3-(4,4-dimethyloxazolin-2-yl)-1,4- dihydropyridyl])-3-tert-butyl(or isopropyl)amino-2-propanols (7-12) were synthesized for evaluation as beta-adrenergic antagonists. Replacement of the naphthyloxy moiety of propranolol by a 1-[1-(4-n-butyl)-3-(4,4-dimethyloxazolin-2-yl)-1,4-dihydropyrid yl] group resulted in a significant decrease in cardiac beta 1-adrenergic antagonist activity which indicates that this group is not a suitable isostere for an aryloxy moiety. 1-(1-[4-n-Butyl-3-(4,4-dimethyloxazolin-2-yl)-1,4-dihydropyridy l])-3- isopropylamino-2-propanol (10) showed a modest beta 2-adrenergic antagonist selectivity for trachea (beta 2/beta 1 = 3:1).

Synthesis and cardioselective beta-adrenergic antagonist activity of quinolyloxypropanolamines.

The synthesis and beta-adrenergic antagonist activities of (2R,2S)-, (2S)-, (2R)-1-(5-quinolyloxy)-3-alkylamino-2-propanols (10-21) and (2R,2S)-1-(5-isoquinolyloxy)-3-alkylamino-2-propanols (24-27) is described. beta 1-Adrenolytic (atria) structure-activity correlations indicated the N-alkyl substituent was a determinant of activity where the relative potency order was i-Pr and t-Bu > cyclohexyl. Compounds having the (2S)-configuration were more potent than the corresponding (2R)-analogs. The position of the heteroaryl nitrogen atom influences potency since the quinolyl analogs were ten-fold more active than the corresponding isoquinolyl isomers. All compounds in both the quinolyl and isoquinolyl series exhibited weak beta 2-adrenolytic activity (trachea), and high beta 1/beta 2 selectivity ratios when the N-alkyl substituent was i-Pr or t-Bu. The quinolyl ring system is an excellent bioisostere for the aryl moiety in aryloxypropanolamines since (2R,2S)- or (2S)-1-(5-quinolyloxy)-3-isopropyl (or t-Bu) amino-2-propanols exhibit very potent and highly cardioselective beta 1-adrenergic antagonist activities.

Synthesis and beta-adrenergic antagonist activity of novel (3-cyanodihydropyridyl)propanolamines.

The synthesis and beta-adrenergic antagonist activities of 1-(1-dihydropyridyl)-3-alkylamino-2-propanols (9-16) in which the aryloxy group of aryloxypropanolamines (1) is replaced by a 1-[2-t-(n-)butyl-3-cyano-1,2-dihydropyridyl] (9-12) or 1-[6-t-(n-)butyl-3-cyano-1,6-dihydropyridyl] (13-16) moiety is described. These replacements resulted in a substantial reduction in beta 1 (atria) and beta 2 (trachea) adrenergic antagonist activities relative to the reference drug metoprolol. Structure-activity correlations indicate the relative potency order is 1,2-dihydropyridyl greater than 1,6-dihydropyridyl, n-Bu greater than t-Bu for dihydropyridyl substituents, and that this class of compounds are non-selective beta-antagonists with a beta 1/beta 2 selectivity ratio close to unity.

Enantioselective syntheses and calcium channel modulating effects of (+)- and (-)-3-isopropyl 5-(4-methylphenethyll) 1,4-dihydro-2,6-dimethyl-4-(2-pyridyl)-3,5-pyridinedicarboxylates.

The (+)- and (-)-enantiomers of 3-isopropyl 5-(4-methylphenethyl) 1,4-dihydro-2,6-dimethyl-4-(2-pyridyl)-3,5-pyridinedicarboxylate were synthesized using an efficient highly enantioselective (ee > or = to 96%) variant of the Hantzsch dihydropyridine synthesis. The key step in this procedure involved the asymmetric Michael addition of a metalated chiral aminocrotonate, derived from D-valine or L-valine, respectively, to the Knoevenagel acceptor (Z)-2-isopropoxycarbonyl-1-(2-pyridyl)-but-1-en-3-one. Both enantiomers exhibited a dual cardioselective partial calcium channel agonist (positive inotropic)/smooth muscle selective calcium channel antagonist effect. The relative in vitro smooth muscle calcium channel antagonist activities of the (-):(+) enantiomers was 26:1. In contrast, the (+)-enantiomer exhibited a greater in vitro positive inotropic effect on guinea pig left atrium where the contractile force was maximally increased by 14.8% at a concentration of 1.63 x 10(-8)M.