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PubMed2003

Estrogenic diazenes: heterocyclic non-steroidal estrogens of unusual structure with selectivity for estrogen receptor subtypes.

Estrogens regulate many biological functions, often acting in a tissue-selective manner. Their tissue-selective action is believed to involve differential estrogen action through the two estrogen receptor (ER) subtypes, ERalpha and ERbeta, as well as differential interaction of the ligand-receptor complexes with promoters and coregulator proteins. In the latter case, selectivity is based on the induction of specific conformations of the ligand-ER complex, conformations that are influenced by the structure of the ligand. Estrogen pharmaceuticals having an ideal balance of tissue-selective activity are being sought for menopausal hormone replacement, breast cancer prevention and therapy, and other actions. To expand on the structural diversity of ER ligands that might show such tissue selectivity, we have prepared a series of diazenes (pyrazines, pyrimidines, and pyridazines) substituted with two to four aryl groups and various short-chain aliphatic substituents. All of the pyrazine and pyrimidines bind to ER, some with high affinity and with a considerable degree of preferential binding to either ERalpha or ERbeta. One pyrimidine and one pyrazine have ERalpha affinity preferences as high as 23 and 9, respectively, and one pyrimidine has an ERbeta affinity preference of 8. The pyridazines, by contrast, are quite polar and have only very low binding affinity for the ER. In cell-based transcription assays, several of the pyrimidines and a pyrazine were found to be considerably more agonistic on ERalpha than on ERbeta. Because these triaryl diazenes have the largest volumes among the ER ligands so far investigated, their high affinity demonstrates the flexibility of the ligand binding pocket of the ERs and its tolerance for large substituents. Thus, these novel heterocyclic ligands expand the repertoire of chemical structures that bind to the estrogen receptor, and they could prove to be useful in elucidating the biological behavior of the two ER subtypes and in forming the basis for new estrogen pharmaceuticals having desirable tissue selectivity.

Endometrial Neoplasms↗

PubMed2006

Supramolecular architectures and magnetic properties of coordination polymers based on pyrazinedicarboxylato ligands showing embedded water clusters.

The synthesis, crystal structure, and magnetic behavior of nine transition-metal complexes based on pyrazine-2,5-dicarboxylato (pz25dc) and pyrazine-2,3-dicarboxylato (pz23dc) ligands are reported. The pz25dc ligand displays a bis-bidentate coordination mode, with the carboxylate groups almost coplanar with the pyrazine ring, to afford polymeric 1-D chains [Mn(1), Fe(2), Zn(3), and Cu(4 and 5)] and discrete dimeric entities [Mn(6)] when the 1,10-phenanthroline (phen) blocking ligand is used to avoid further polymerization. The nonplanar pz23dc ligand chelates to a unique copper center, while it bridges another one or two metal centers via the remaining carboxylate group, leading to 1-D polymeric chains (7), ladder chains (8), and sheets (9). The crystal packing of the metal-organic frameworks of compounds 4-9 generates voids which are occupied by assembled water molecules. The different water cluster patterns (tapes, four-membered discrete rings, and chains for compounds 6, 8, and 9, respectively) and their role in the cohesiveness of supramolecular architectures are analyzed. Thermogravimetric and variable-temperature X-ray powder diffraction studies have revealed the occurrence of reversible dehydration processes in compounds 6, 8, and 9. Furthermore, the magnetic behavior of these compounds has been studied in order to analyze the capability of the pyrazine ring to transmit magnetic interactions.

Journal Article↗

PubMed1999

Nanoporous, Interpenetrated Metal-Organic Diamondoid Networks.

Reactions of Cd(NO(3))(2).4H(2)O with 4-cyanopyridine in the presence of ethanol or pyrazine guest molecules under hydro(solvo)thermal conditions afford two new cadmium coordination polymers, [Cd(isonicotinate)(2)(EtOH)][EtOH], 1, and [Cd(isonicotinate)(2)(H(2)O)][pyrazine], 2. The Cd centers in both 1 and 2 are seven-coordinate with distorted pentagonal bipyrimidal structures via coordination to two pyridyl nitrogen atoms, one oxygen atom from a solvent molecule, one chelating carboxylate, and one semichelating carboxylate group. The bridging isonicotinate groups link each Cd center to four adjacent Cd centers, resulting in three-dimensional polymeric networks based on doubly interpenetrated diamondoid structures. One molecule of ethanol or pyrazine is also included in 1 or 2, respectively, to fill the void space left within the solid after the twofold interpenetration. Thermogravimetric analyses (TGA) showed that the included and coordinated ethanol molecules in 1 could be removed stepwise at 100 and 160 degrees C, respectively. After the removal of the guest ethanol molecules, the resulting nanoporous solid exhibits the same X-ray powder diffraction (XRPD) pattern as 1. Guest ethanol molecules can be reintroduced into the evacuated sample of 1 via exposure to ethanol vapor at room temperature. Further heating results in the loss of coordinated ethanol molecules and the collapse of the polymeric network structure. On the other hand, XRPD shows that removal of pyrazine in 2 is accompanied by the loss of the coordinated water molecules and, consequently, the collapse of the polymeric network structure. These results demonstrate that nanopores can be designed based on interpenetrated coordinated networks. Crystal data for 1: orthorhombic space group Pbca, a = 12.691(1) Å, b = 15.545(1) Å, c = 18.342(1) Å, and Z = 8. Crystal data for 2: orthorhombic space group Pbca, a = 12.081(1) Å, b = 15.323(2) Å, c = 19.705(3) Å, and Z = 8.

Journal Article↗

PubMed2005

Dinuclear bis-beta-diketonato ligand derivatives of iron(III) and copper(II) and use of the latter as components for the assembly of extended metallo-supramolecular structures.

A range of 1,3-aryl linked, bis-beta-diketone derivatives (LH2) has been employed to synthesise neutral bis(ligand), dinuclear complexes incorporating square-planar copper(II) and tris(ligand) dinuclear helical derivatives containing octahedral iron(III). The 1H NMR spectra of the free ligands contain singlet peaks at ca. 16.2 ppm, indicative of enolic protons, confirming that the (bis) enol tautomer is present in solution. An X-ray structure of a ligand from the series incorporating tert-butyl terminal substituents confirms that the same tautomer persists in the solid and that the relative orientation of the bis-beta-diketone fragments is such that the coordination vectors lie at approximately 120 degrees to each other. The planar, dinuclear copper complexes form 1 : 2 adducts with pyridine and 4-(dimethylamino)pyridine, confirmed by X-ray structures, that incorporate five-coordinate metal centres. Based on this behaviour, the prospect of linking copper centres in the dinuclear complexes using the difunctional heterocyclic bases, 4,4'-bipyridine, 4,4'-trans-azopyridine and pyrazine as co-ligands has been probed. However, 4,4'-bipyridine was observed to coordinate through only one of its heterocyclic nitrogen atoms in the solid state to form a 1 : 2 ([Cu2(L)2]: 4,4'-bipyridine) adduct, analogous to the structures obtained with the above mono-functional nitrogen bases. Nevertheless, an X-ray structure determination shows that the related difunctional base, 4,4'-trans-azopyridine, coordinates in a bridging fashion via both its heterocyclic nitrogen atoms on alternate sides of each planar [Cu2(L)2] unit to produce an infinite one dimensional metallo chain. In contrast, with pyrazine, a new neutral, discrete assembly of type [Cu4(L)4(pyrazine)2] is formed. The X-ray structure shows that two planar dinuclear complexes are linked by two pyrazine molecules in a sandwich arrangement such that the coordination environment of each copper ion is approximately square pyramidal with the overall tetranuclear structure thus taking the form of a 'dimer of dimers'.

Journal Article↗

PubMed2006

Cigarette smoke toxicants alter growth and survival of cultured mammalian cells.

Our purpose was to determine the effects of six cigarette toxicants (pyridine, nicotine, 2-ethylpyridine, 3-ethylpyridine, p-cresol, and pyrazine) on three types of cultured mammalian cells (human umbilical vein endothelial cells [HUVECs], human microvascular endothelial cells [HMVECs], and NIH 3T3 cells) using a cell proliferation/survival assay. Synchronized cells were cultured in proliferation or survival medium containing various doses (10(-18)M-10(-2)M) of the tested chemicals. After 48 h, cells were counted using a hemacytometer. The no observable adverse effect level (NOAEL), lowest observable adverse effect level (LOAEL), and the efficacy were determined for each compound in the cell proliferation and survival assays. Pyridine and p-cresol did not show significant effects with any cell types, except at high doses. Derivitization of the pyridine ring altered its potency, especially when an ethyl group or nitrogen was added. In survival medium, nicotine stimulated proliferation of all three cell types at doses found in smoker's serum (10(-8)M-10(-7)M). For HUVEC and HMVEC, 2-ethylpyridine, 3-ethylpyridine, and pyrazine inhibited proliferation in proliferation medium and induced cell death in survival medium at attomolar and femtomolar doses. All chemicals, except pyridine and pyrazine, stimulated NIH 3T3 cell proliferation at low doses and induced cell death at high doses. LOAELs and efficacies revealed that endothelial cells from a developing organ (umbilical cord) were more sensitive to these chemicals than endothelial cells from an adult organ (lung). 3-Ethylpyridine and pyrazine, which induced cell death at low doses, are added to consumer products and should be subjected to further toxicological testing.

Animals↗

PubMed2000

Oligosiloxanediols as building blocks for supramolecular chemistry: hydrogen-bonded adducts with amines form supramolecular structures in zero, one and two dimensions

The structure of 1,1,3,3,5,5-hexaphenyltrisiloxane-1,5-diol-pyrazine (4/1), (C36H32O4Si3)4.C4H4N2 (1), contains finite centrosymmetric aggregates; the diol units form dimers, by means of O-H...O hydrogen bonds, and pairs of such dimers are linked to the pyrazine by means of O-H...N hydrogen bonds. In 1,1,3,3,5,5-hexaphenyltrisiloxane-1,5-diol-pyridine (2/3), (C36H32O4Si3)2.(C5H5N)3 (2), the diol units are linked into centrosymmetric pairs by means of disordered O-H...O hydrogen bonds: two of the three pyridine molecules are linked to the diol dimer by means of ordered O-H...N hydrogen bonds, while the third pyridine unit, which is disordered across a centre of inversion, links the diol dimers into a C3(3) (9) chain by means of O-H...N and C-H...O hydrogen bonds. In 1,1,3,3-tetraphenyldisiloxane-1,3-diol-hexamethylenetetramine (1/1), (C24H22O3Si2).C6H12N4 (3), the diol acts as a double donor and the hexamethylenetetramine acts as a double acceptor in ordered O-H...N hydrogen bonds and the structure consists of C2(2) (10) chains of alternating diol and amine units. In 1,1,3,3-tetraphenyldisiloxane-1,3-diol-2,2'-bipyridyl (1/1), C24H22O3Si2.C10H8N2 (4), there are two independent diol molecules, both lying across centres of inversion and therefore both containing linear Si-O-Si groups: each diol acts as a double donor of hydrogen bonds and the unique 2,2'-bipyridyl molecule acts as a double acceptor, thus forming C2(2) (11) chains of alternating diol and amine units. The structural motif in 1,1,3,3-tetraphenyldisiloxane-1,3-diol-pyrazine (2/1), (C24H22O3Si2)2. C4H4N2 (5), is a chain-of-rings: pairs of diol molecules are linked by O-H...O hydrogen bonds into centrosymmetric R2(2) (12) dimers and these dimers are linked into C2(2) (13) chains by means of O-H...N hydrogen bonds to the pyrazine units. 1,1,3,3-Tetraphenyldisiloxane-1,3-diol-pyridine (1/1), C24H22O3Si2.C5H5N (6), and 1,1,3,3-tetraphenyldisiloxane-1,3-diol-pyrimidine (1/1), C24H22O3Si2.C4H4N2 (7), are isomorphous: in each compound the amine unit is disordered across a centre of inversion. The diol molecules form C(6) chains, by means of disordered O-H...O hydrogen bonds, and these chains are linked into two-dimensional nets built from R6(6) (26) rings, by a combination of O-H...N and C-H...O hydrogen bonds.

Journal Article↗

PubMedDate not supplied

Aminopyrazine analogues as chemiluminescence derivatization reagents for pyruvic acid.

Aminopyrazine analogues were studied as sensitive and selective chemiluminescence derivatization reagents for pyruvic acid. These analogues reacted with pyruvic acid under acidic conditions at 100 degrees C to produce Cypridina luciferin derivatives, which exhibit chemiluminescence by reaction with hydrogen peroxide in the presence of potassium t-butoxide in dimethylformamide. Of the four aminopyrazine analogues (2-amino-5-phenylpyrazine, 2-amino-5-(4-hydroxyphenyl)pyrazine, 2-amino-5-(3,4, 5-trimethoxyphenyl)pyrazine, and 2-aminoquinoxaline), in the present test 2-amino-5-(3,4,5-trimethoxyphenyl) pyrazine was the most sensitive for pyruvic acid, and the chemiluminescence intensity was about four times higher than that obtained with aminopyrazine.

Indicators and Reagents↗

PubMedDate not supplied

Light-emitters involved in the luminescence of coelenterazine.

Coelenterazine emits light by chemi-and bioluminescence reactions, decomposing into coelenteramide and CO(2). To ascertain the light emitters involved, the fluorescence of coelenteramide and five analogues were studies in four kinds of solvent. The results showed that coelenteramides can form five kinds of light emitters, ie unionized (lambda(max) 386-423 nm), phenolate anion (lambda(max) 480-490 nm), phenolate anion temporarily formed from the ion-pair state (lambda(max) 465-479 nm), amide anion (lambda(max) 435-458 nm) and pyrazine-N(4) anion (lambda(max) 530-565 nm). The chemiluminescence light emitter of coelenterazine in the presence of alkali (lambda(max) 530-550 nm) was found to be the pyrazine-N(4) anion and not the dianion (ie phenolate anion/amide anion), as previously believed. In chemiluminescence, the normal light emitter is the amide anion, and the pyrazine-N(4) anion emission may occur in the presence of alkali, but light emission from any other emitters has not been observed. In the bioluminescence reaction, the normal light emitter is the amide anion, but no other light emitter was observed except the unionized form found in the Ca-triggered luminescence of semisynthetic aequorins prepared with an e-type coelenterazine instead of coelenterazine.

Aequorin↗

PubMedDate not supplied

Development of imidazopyrazinone red-chemiluminescent probes for detecting superoxide anions via a chemiluminescence resonance energy transfer method.

During the development of useful probes for detecting superoxide anions via chemiluminescence with longer wavelengths than that of green, chemiluminescent probes that emit red light (lambda(max) 610 nm) when induced by superoxide anions were synthesized and characterized. These red-chemiluminescent probes consist of a 6-(4-methoxyphenyl)imidazo[1,2-a] pyrazin-3(7H)-one moiety, which reacts with superoxide anions to generate energy, and a sulphorhodamine 101 moiety, which accepts the energy and emits red light. Using a hypoxanthine-xanthine oxidase system for the generation of superoxide anions, it was shown that the superoxide anion-induced chemiluminescences of red-chemiluminescent probes (3 and 4) were more intense than those of the blue- and green-chemiluminescent probes 2-methyl-6-(4-methoxyphenyl)imidazo[1,2-a] pyrazin-3(7H)-one (MCLA) and 6-[4-[2-[N'-(5-fluoresceinyl)thioureido]-ethoxy]phenyl]-2-methylimidazo[1,2-a]pyrazin-3(7H)-one (FCLA), respectively, which are generally considered to be the most sensitive chemiluminescent probes. The ratio between the superoxide-dependent and background chemiluminescence intensities for 3 was comparable to those of MCLA and FCLA, but higher than that of 4. Due to its highly intense superoxide anion-induced chemiluminescence at low probe concentrations, red-chemiluminescent probe 3 is superior to MCLA and FCLA for measurement of superoxide anions.

Energy Transfer↗

PubMed2004

Novel CuIII bis-1,2-dichalcogenene complexes with tunable 3D framework through alkaline cation coordination: a structural and theoretical study.

The deprotonated form of the ligands pyrazine-2,3-diselenol (pds) and pyrazine-2,3-dithiol (pdt) react with Cu(ClO(4))(2).6 H(2)O to form different Cu(III) complexes Na[Cu(III)(pds)(2)].2 H(2)O (1), Li[Cu(III)(pds)(2)].3 H(2)O (2), and Na[Cu(III)(pdt)(2)].2 H(2)O (4) depending on the countercation compound used as deprotonating agent (NaOH, LiOH). Two other Cu(III) complexes were obtained by replacement of the alkali metal cations with tetrabutylammonium (TBA(+)), namely, TBA[Cu(III)(pds)(2)] (3), and TBA[Cu(III)(pdt)(2)] (5). All complexes were characterized by (1)H and (13)C NMR and IR spectroscopy, electronic absorption, elemental analysis, cyclic voltammetry (CV), and X-ray crystallography. Electrical conductivity measurements on single crystals show that these salts exhibit insulating behavior. The crystal structure of these species revealed a lateral coordination capability of the N atoms of the pyrazine ring of both pds and pdt ligands towards the alkali metal ions, which leads to the build up of a net of coordinative bonds, hydrogen bonds, and contacts that result in the final 3D structure. Two parameters control the crystal engineering of the final 3D structures: the nature of the alkali metal countercation and the nature of the chalcogen atom (Se/S), which allow fine-tuning of complex 3D crystal lattice. Density functional calculations were performed on the [Cu(pds)(2)] and [Cu(pdt)(2)] systems to investigate the electronic structure of the complexes and understand their electronic and electrochemical behavior by studying the frontier molecular orbitals. This study also reveals whether the redox processes take place on the ligands or on the metal center, a question under continuous discussion in the literature.

Alkalies↗

PubMed1989

A possible mechanism of action of tetramethylpyrazine on vascular smooth muscle in rat aorta.

The vasodilatation of isolated rat aorta by tetramethylpyrazine (TMP) was studied by examining its effect on phenylephrine-induced contraction. We found no difference between the effects on intact and on endothelium-denuded preparations. The effect of TMP was similar to that of theophylline because propranolol did not block the vasodilatation. Also, there was a summation effect when the pyrazine was combined with theophylline. Furthermore, like that due to theophylline, the vasodilatation was accompanied by an increase in cyclic AMP. The pyrazine, as do other dilators, affected differently the two separate phases of the contractile response elicited with either phenylephrine or high potassium. The drug predominantly suppressed the phasic responses but both the phasic and tonic phases could be inhibited significantly if the concentration of the pyrazine was high enough. The present results suggest that intracellular accumulation of cyclic AMP and blockade of the release of calcium from internal stores may be important elements of the mechanism by which TMP reduces the development of tension in rat aortic smooth muscle.

Animals↗

PubMed2003

Calculated gas-phase infrared spectra of imidazo[1,2-a]pyrazinediones derived from alanine.

IR spectra of bicyclic and tricyclic amidine derivatives of alanine (2,5,8-trimethylhexahydroimidazo[1,2-a]pyrazine-3,6-dione, 2,5,8-trimethyltetrahydroimidazo[1,2-a]pyrazine-3,6-dione and 2,5,7,10-tetramethylhexahydroimidazo[1,2-a]imidazo[1,2-d]pyrazine-3,8-dione) were computed by the HF, B3LYP, B3P86 and B3PW91 methods in conjunction with the 6-31G(d) basis set. The IR spectra calculated are in a good agreement with the observed FTIR spectra. The correlation between the calculated and experimental vibration frequencies is characterized by the coefficients of 0.9997 for all three DFT methods; for HF it is about 0.9992. The calculated absolute band intensities satisfactory match the observed relative intensities. Optimal uniform scaling factors calculated for this series of compounds are 0.8967, 0.9598, 0.9544 and 0.9555 for HF, B3LYP, B3P86 and B3PW91, respectively. Taking into account small variations of the scaling factors for the derivatives of different amino acids, for future IR spectral predictions for unknown compounds of this class, one can recommend scaling factors of 0.897, 0.959, 0.954 and 0.955 for HF, B3LYP, B3P86 and B3PW91, respectively.

Alanine↗

PubMed2001

Effects of olive, canola, and sunflower oils on the formation of volatiles from the Maillard reaction of lysine with xylose and glucose.

Some important edible oils (extra virgin olive oil, canola oil, and sunflower oil) were added to aqueous glucose-lysine or xylose-lysine model systems to investigate their effect on the formation of volatiles from the Maillard reaction (MR). The volatile compounds were extracted by a Likens-Nickerson apparatus and quantified. Pyrazines, Maillard reaction products with an important impact on food flavor, appeared to be particularly sensitive to the presence of the oils in both the xylose-lysine and glucose-lysine model systems. The unsubstituted pyrazine was formed more with olive oil, less with canola oil, and even less with sunflower oil, whereas 2-methylpyrazine, 2,5-methylpyrazine, and 2,3-dimethylpyrazine were formed less with olive oil, more with canola oil, and even more with sunflower. The oxidative states of the oils and their fatty acid fingerprints were determined: the results indicated that the relative amounts of the pyrazines are sensitive to the degree of unsaturation of the oil. The autoxidation of the volatile compounds generated from the MR, investigated by the addition of free radical modulators (antioxidants alpha-tocopherol, 2,6-di-tert-butyl-4-methylphenol, and rosemary extract; or pro-oxidant alpha,alpha'-azobis-isobutyronitrile, a free radical initiator), was limited in respect to aqueous model systems.

Fatty Acids↗

PubMed2003

Comparison of natural and roasted Turkish tombul hazelnut (Corylus avellana L.) volatiles and flavor by DHA/GC/MS and descriptive sensory analysis.

Natural (raw) and roasted hazelnuts were compared for their differences in volatile components and sensory responses. A total of 79 compounds were detected in both hazelnuts, of which 39 (27 positive, 5 tentative, and 7 unknown) were detected in natural hazelnut and 71 (40 positive, 14 tentative, and 17 unknown) were detected in roasted hazelnut. These included ketones, aldehydes, pyrazines, alcohols, aromatic hydrocarbons, furans, pyrroles, terpenes, and acids. Pyrazines, pyrroles, terpenes, and acids were detected in roasted hazelnut only. Concentrations of several compounds increased as a result of roasting and these may play significant roles in the flavor of roasted hazelnut. Pyrazines together with ketones, aldehydes, furans, and pyrroles may contribute to the characteristic roasted aroma of hazelnut. Descriptive sensory analysis (DSA) showed that some flavor attributes such as "aftertaste", "burnt", "coffee/chocolate-like", "roasty", and "sweet" were rated significantly higher in roasted hazelnut compared to its natural counterpart. Natural and roasted hazelnuts can be distinguished using these attributes.

Aldehydes↗

PubMed2006

Identification of components responsible for the odor of cigar smoker's breath.

Following smoking 1/2 of a cigar, the most odorous cigar tobacco smoke components extracted from the surface of the tongue by nylon-meshed swabs and then extracted from the swab headspace by solid phase microextraction were ethyl pyrrole, 2,3-dimethyl pyrazine, and 2-ethyl pyridine. Similar classes of compounds were identified from the headspace of an aqueous simulated saliva solution treated with cigar smoke. The most odorous compounds were 2,3,5-trimethyl pyridine, 2,5-dimethyl pyrazine, and 2-ethyl-3,5-dimethyl pyridine. Pyridines and pyrazines, the most prominent classes of odorous compounds identified in this experiment, may be generated during cigar pyrrolysis by cleavage of nicotine or by Maillard reaction.

Breath Tests↗

PubMed1996

Construction of a quantitative three-dimensional model for odor quality using comparative molecular field analysis (CoMFA).

A quantitative structure-activity relationship (QSAR) study of odorants was performed taking an odor as an activity. As an example, we took the 'green odor of pyrazine derivations' as an activity. Conformational analysis of the pyrazine derivatives was performed, and conformers were selected using the longest side-length of a circumscribed box (LLCB) as a criterion. Comparative molecular field analysis (CoMFA) was used to elucidate the three-dimensional (3D) structural features of the derivatives. As a result, it was found that the steric and electrostatic features of the derivations were correlated with human olfactory detection threshold values. We constructed a quantitative 3D model using the graphic views of CoMFA and partial structures of the derivatives. The prediction of human olfactory detection threshold values of other pyrazine derivatives with green odor was possible by using the 3D model. As another example, we took the 'sweet odor of compounds with various structures' as an activity. A quantitative 3D model for sweet odor was constructed in the same manner. Analysing the structural features of odorants by CoMFA and constructing 3D models for several important odor qualities would help to (i) explain or predict human olfactory detection threshold values of interesting odorants, (ii) design new odorants by suggesting the steric and electrostatic requirements, and (iii) elucidate the mechanism of odorant-receptor interaction.

Aldehydes↗

PubMed1968

Amiloride: a potent inhibitor of sodium transport across the toad bladder.

1 Amiloride inhibits Na transport and short-circuit current (SCC) across the toad bladder. It is 1000 times more active at the mucosal than serosal surface. The lowest effective concentration was 10(-7)M.2. The inhibition was non-competitive with the sodium on the mucosal side of the bladder.3. Vasopressin, cyclic adenosine monophosphate (AMP) and aldosterone increased Na transport and SCC across the bladder and these effects were inhibited by amiloride.4. The antagonism of amiloride for vasopressin was non-competitive.5. Amphotericin B also increases Na transport across the bladder but its action was not changed by amiloride.6. Amiloride was without effects on SCC and diffusion potentials in bladders metabolically inhibited with CN(-) and iodoacetic acid (IAA).7. Neither plasma albumin, Ca(2+) nor adenosine triphosphate (ATP) altered the effects of amiloride.8. The only structural analogue of amiloride found to reduce SCC similarly was guanidine which was 1000 times less active. Pyrazine and a substituted pyrazine analogue were without effect. Neither guanidine nor the substituted pyrazine compound were competitive with amiloride.9. Amiloride had no effect on the osmotic permeability of the toad bladder either in the presence or absence of vasopressin.10. Na transport across the toad colon was also reduced by 10(-5)M amiloride at the mucosal surface.11. The possible mechanism of action of amiloride is discussed.

Adenine Nucleotides↗

PubMed1993

[Studies on as-triazine derivatives. XIX. Synthesis of 2,3-diarylpyrazine 2,3-diarylpyridine derivatives as blood platelet aggregation inhibitors].

4,5-Diphenyl-2-ethoxypyrimidine (1), 3,4-diphenyl-6-ethoxypyridazine (2) and 2,3-diphenyl-5-ethoxypyrazine (3) were evaluated for inhibitory activity towards arachidonic acid-induced aggregation of rabbit blood platelet in vitro. 2,3-Diphenyl-5-ethoxypyrazine (3) exhibited significant inhibitory activity. Thus, various 5-substituted 2,3-bis(4-methoxyphenyl)pyrazines were synthesized by the nucleophilic substitution reaction of 5-chloro-2,3-bis(4-methoxyphenyl)pyrazine (9). In a similar manner, substituted 2,3-bis(4-methoxyphenyl)pyridines were prepared from 2,3-bis(4-methoxyphenyl)-6-methylsulfonylpyridine (17), which was synthesized by the cycloaddition retro Diels-Alder reaction of 5,6-bis(4-methoxyphenyl)-3-methylsulfonyl-1,2,4-triazine (16) with norbornadiene. Among the compounds prepared, 6-isopropoxy-2,3-bis(4-methoxyphenyl)-pyrazine (10f) showed the most potent inhibitory activity, which was more than the activity of anitrazafen[5,6-bis(4-methoxyphenyl)-3-methyl-1,2,4-triazine.

Animals↗