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Synthesis of pyrazine-phosphonates and -phosphine oxides from 2H-azirines or oximes.

[reaction: see text] Tetrasubstituted pyrazines containing two phosphonate groups 2 in positions 2 and 5 and trisubstituted pyrazines containing a phosphonate 5 or a phosphine oxide group 7 in position 2 are obtained by thermal treatment of 2H-azirine-2-phosphonates 1 and -phosphine oxides 6. These pyrazines can also be prepared from beta-ketoxime tosylates 9 and 10 or from oxime derived from phosphine oxide 11.

Azirines↗

A phase II trial of pyrazine diazohydroxide in patients with disseminated malignant melanoma and no prior chemotherapy--Southwest Oncology Group study.

Malignant melanoma is rapidly increasing in the United States. Metastatic disease responds poorly to currently available chemotherapy. Pyrazine diazohydroxide (PZDH) is a new agent inhibiting DNA synthesis that is active in mouse tumor models and human xenografts and lacks cross resistance with multiple standard agents. In this phase II trial, patients with no prior chemotherapy or immunotherapy for metastatic disease and performance status (SWOG) of 0-1, were treated with pyrazine diazohydroxide at a dose of 100 mg/m2/day by i.v. bolus injection over 5-15 minutes for 5 consecutive days every 6 weeks. There were 23 eligible patients entered on this trial with 74% having PS of 0 and 91% having visceral metastases. There were no confirmed anti-tumor responses. The overall response rate is 0% (95% CI 0%-15%). Median overall survival is six months (95% CI 5-8 months). The most common toxicities were hematologic and consisted of lymphopenia, thrombocytopenia, anemia, and leukopenia. Fatigue. and nausea and vomiting were the next most common toxicities. Pyrazine diazohydroxide by this dose and schedule has insufficient activity in the treatment of disseminated malignant melanoma to warrant further investigation.

Adult↗

Speculating about pyrazines.

Of the various types of alerting signals found in nature, odours are the least well understood. The worldwide distribution of pyrazines in plants, insects, terrestrial vertebrates, marine organisms, fungi and bacteria suggests that they are of special significance. We speculate that these molecules served as natural points of convergence in the evolution of widespread alerting signals, which are used for differing but related intraspecific purposes by various species. In aposematic, self-advertising toxic insects and their mimics, for example, pyrazines function as additional warning signals; preliminary data indicates that their odour can potentiate taste aversion learning in rats and the associative learning of immune suppression in mice. The latter suggests that in addition to their alerting properties, pyrazine odours may act as ectohormones which interact with predator physiology.

Animals↗

Antithrombotic activity of a new pyrazine derivative determined by the mouse antithrombotic assay.

A model of pulmonary microembolization in the mouse induced by infusion of epinephrine and collagen was used to determine antithrombotic activity of indomethacin and acetylsalicylic acid and of two newly synthesized pyrazine derivatives. One of the new agents provided marked protection of mice from thrombotic challenge with epinephrine and collagen. Its effectiveness was higher than acetylsalicylic acid (especially at small doses) but smaller than that of indomethacin. The same compound was similar to acetylsalicyclic acid with respect to the inhibition of in vitro human blood platelet aggregation. The new class of pyrazine derivatives (the so-called pyrazine CH- and NH-acids) appears interesting from the view-point of the studies of platelet aggregation and may yield potential antithrombotic drugs.

Animals↗

Modulation of the megakaryoblastic Dami cell line differentiation by phosphodiesterase inhibitors and imidazo[1,2-a]pyrazine derivatives.

Phosphodiesterase inhibitors have been shown to modulate cell differentiation. We have previously shown that a series of imidazo[1,2-a]pyrazine derivatives displayed inhibitory effects on phosphodiesterase isoenzymes types III. IV and V isolated from Dami cells and on Dami cell growth. In the present study we have investigated the effect of these derivatives on the expression of two differentiation markers, glycoproteins Ib and IIb/IIIa of the human megakaryoblastic leukaemic Dami cell line in comparison to those elicited by 3-isobutyl-1-methylxanthine and selective phosphodiesterase inhibitors of types 1 (8-methoxymetyl-1-methyl-3-(2-methylpropyl) xanthine), III (Milrinone), IV (RO-201724) and V (Zaprinast). Imidazo[1,2-a]pyrazine derivatives, 3-isobutyl-1-methylxanthine and selective phosphodiesterase inhibitors, except 8-methoxymethyl-1-methyl-3-(2-methylpropyl) xanthine, decreased glycoprotein Ib expression. SCA40, SCA41, SCA44 and 3-isobutyl-1-methylxanthine-but not the other compounds affected the expression of glycoprotein IIb/IIIa in a positive manner. The effects of imidazo[1,2-a]pyrazine derivatives on glycoprotein expression appeared to be related to their phosphodiesterase inhibitory potency.

Cell Differentiation↗

Discovery of pyrrolo[2,3-b]pyrazines derivatives as submicromolar affinity activators of wild type, G551D, and F508del cystic fibrosis transmembrane conductance regulator chloride channels.

The cystic fibrosis transmembrane conductance regulator (CFTR) represents the main Cl(-) channel in the apical membrane of epithelial cells for cAMP-dependent Cl(-) secretion. Here we report on the synthesis and screening of a small library of 6-phenylpyrrolo[2,3-b]pyrazines (named RP derivatives) evaluated as activators of wild-type CFTR, G551D-CFTR, and F508del-CFTR Cl(-) channels. Iodide efflux and whole-cell patch-clamp recordings analysis identified RP107 [7-n-butyl-6-(4-hydroxyphenyl)[5H]-pyrrolo[2,3-b]pyrazine] as a submicromolar activator of wild-type (WT)-CFTR [human airway epithelial Calu-3 and WT-CFTR-Chinese hamster ovary (CHO) cells], G551D-CFTR (G551D-CFTR-CHO cells), and F508del-CFTR (in temperature-corrected human airway epithelial F508del/F508del CF15 cells). The structural analog RP108 [7-n-butyl-6-(4-chlorophenyl)[5H]pyrrolo[2,3-b]pyrazine], contrary to RP107, was a less potent activator only at micromolar concentrations. RP107 and RP108 did not have any effect on the cellular cAMP level. Activation was potentiated by low concentration of forskolin and inhibited by glibenclamide and CFTR(inh)-172 [3-[(3-trifluoromethyl)phenyl]-5-[(4-carboxyphenyl-)methylene]-2-thioxo-4-thiazolidinone]but not by calixarene or DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid). Finally, we found significant stimulation of short circuit current (I(sc)) by RP107 (EC(50) = 89 nM) and RP108 (EC(50) = 103 microM) on colon of Cftr(+)(/)(+) but not of Cftr(-/-) mice mounted in Ussing chamber. Stimulation of I(sc) was inhibited by glibenclamide but not affected by DIDS. These results show that RP107 stimulates wild-type CFTR and mutated CFTR, with submicromolar affinity by a cAMP-independent mechanism. Our preliminary structure-activity relationship study identified 4-hydroxyphenyl and 7-n-butyl as determinants required for activation of CFTR. The potency of these agents indicates that compounds in this class may be of therapeutic benefit in CFTR-related diseases, including cystic fibrosis.

Animals↗

Research on heterocyclic compounds. X.-Imidazo[1,2-a]pyrazine derivatives: synthesis and antiinflammatory activity.

Since we had previously observed the considerable anti-inflammatory activity of imidazo[1,2-a]pyrazine 2-acetic acid, we prepared a series of imidazo[1,2-a]pyrazine derivatives, bearing some substituents on the pyrazine ring and a carboxylic, acetic or alpha-methylacetic moiety on the imidazole ring. These new compounds were tested for antiinflammatory, analgesic, antipyretic and ulcerogenic activities.

Analgesics↗

Syntheses and cytotoxicity evaluation of bis(indolyl)thiazole, bis(indolyl)pyrazinone and bis(indolyl)pyrazine: analogues of cytotoxic marine bis(indole) alkaloid.

2,4-Bis(3'-indolyl)thiazoles, 3,5-bis(3'-indolyl)-2(1H)pyrazinone and 3,6-bis(3'-indolyl)pyrazine were synthesized and evaluated for cytotoxic activity against diverse human cancer cell lines by the National Cancer Institute. These compounds demonstrated significant inhibitory effects in the growth of a range of cancer cell lines. 2,4-Bis(3'-indolyl)thiazole displayed selective cytotoxicity against certain leukemia cell lines with GI50 values in the low micromolar range while the substituted derivatives showed a broad spectrum of cytotoxic activity. 3,5-Bis(3'-indolyl)-2(1H)pyrazinone and 3,6-bis[3'-(N-methyl-indolyl)]pyrazine possessed strong inhibitory activity against a wide range of human tumor cell lines. The mechanism of action remained unknown. The results suggested that 2,4-bis(3'-indolyl)thiazoles, 3,5-bis(3'-indolyl)-2(1H)pyrazinone and 3,6-bis[3'-(N-methyl-indolyl)] pyrazine offer potential as lead compounds for the discovery of anticancer agents.

Antineoplastic Agents↗

Low-energy ion--surface reactions of pyrazine with two classes of self-assembled monolayers: influence of alkyl chain orientation

Collisions of pyrazine with two classes of self-assembled monolayer (SAM) films are employed to determine whether surface confinement and the resulting alkyl chain orientation, influences low-energy ion-surface reactions. SAM films formed from n-alkanethiols (CH3(CH2)n-S-Au, n = 14-17) and 4-(4-alkoxyphenylbenzenethiols (4-(4-CH3(CH2)mOC6H4)-C6H4-S-Au, m = 14-17) chemisorbed onto Au (111) substrates are known to exhibit a chain-length-dependent odd-even effect that places the terminal C-C bond into different orientations. Ion-surface collisions (20 eV) of pyrazine molecular ion (M = m/z 80) with these surfaces yield reaction product ions corresponding to the addition of hydrogen atoms ([M + H]+ = m/z 81) and methyl groups ([M + CH3]+ = m/z 95) from the surface to the probe ion. Differences in the relative abundance of the reaction product ions are measured as a function of chain length for both classes of SAM film. SAM films with odd chain lengths (n, m = 14 and 16) have a consistently higher abundance of H addition product ions than SAM films with even chain lengths (n, m = 15 and 17). Alternating reactivity is also observed for the addition of CH3, with methyl addition occurring more readily on even-chain-length films. The variations are consistent with the well-characterized orientation differences known to exist for films of this type. Specifically, odd-chain-length films are oriented such that the last C-C bond is more parallel to the plane of the surface than it is for even-chain-length films. The critical element of the parallel orientation is that it leaves, on average, one hydrogen atom on the terminal methyl and both hydrogen atoms on the first underlying methylene in more reactive positions compared to even chain lengths. Conversely, the trend in the relative abundance of CH3 addition indicates that the orientation produced by an even-chain-length film, with the last C-C bond more perpendicular to the surface, allows the probe ion better access to the methyl carbon. Reflection absorption IR spectroscopy (RAIRS) data independently confirm the orientational disposition of the films. The RAIRS data show that the odd-even effect is less dramatic for the n-alkanethiols when compared to 4-(4-alkoxyphenyl)benzenethiols. A smaller difference in ion-surface reactivity is measured for n-alkanethiols, demonstrating that ion-surface reactions can distinguish subtle differences in average orientation. In short, we report that the extent of ion-surface reactions of pyrazine ion with two classes of SAM films is directed by the spatial orientation of the surface-confined species that participate in the reaction.

Journal Article↗

Infrared activity of symmetric bridging ligand modes in pyrazine-bridged hexaruthenium mixed-valence clusters.

A fully symmetric (A(g)) vibrational mode of pyrazine is observed in the infrared spectrum of four pyrazine-bridged hexaruthenium mixed-valence complexes with varying degrees of electronic coupling between clusters. Deuteration of the bridging pyrazine ligand and the accompanying shift in frequency confirm the assignment of this mode. Previous observation of infrared line coalescence in the carbonyl stretching region assigns all of these complexes to Robin-Day class II (partial localization of charge) on the picosecond time scale. The infrared activity of the fully symmetric bridging ligand mode could provide a complementary assignment of these complexes to class II on a faster, femtosecond time scale. However, the extinction coefficient for this band is much greater than that observed in similar asymmetric, non-mixed-valence complexes and suggests that its strong IR activity is due to vibronic enhancement rather than electronic asymmetry.

Journal Article↗

Homo- and Heteronuclear Ruthenium and Osmium Complexes Containing an Asymmetric Pyrazine-Based Bridging Ligand.

The synthesis, characterization, and electrochemical, photophysical, and photochemical properties of the compounds [Ru(bpy)(2)(L)](2+) (Ru), [Os(bpy)(2)(L)](2+) (Os), [(L)Os(bpy)(2)Cl](+) (OsCl), [Ru(bpy)(2)(L)Ru(bpy)(2)Cl](3+) (RuRuCl), [Os(bpy)(2)(L)Os(bpy)(2)Cl](3+) (OsOsCl), [Ru(bpy)(2)(L)Os(bpy)(2)Cl](3+) (RuOsCl), and [Os(bpy)(2)(L)Ru(bpy)(2)Cl](3+) (OsRuCl) are reported (bpy = 2,2'-bipyridine, L = 1-methyl-3-(pyrazin-2-yl)-1,2,4-triazole). The Os(bpy)(2) and the Ru(bpy)(2) moieties are coordinated to the pyrazyltriazole ligand in two different ways, i.e. in a bidentate fashion via the triazole ring and N1 of the pyrazine ring and in a monodentate fashion only via N4 of the pyrazine ring. In the homonuclear dimers the monodentate bound metal has an oxidation potential that is approximately 400 mV lower than that of the bidentate bound metal. Spectroelectrochemical investigations suggest the presence of a weak interaction between the metal centers in the dinuclear species. The emission properties of the compounds are indicative of efficient energy transfer in the excited state, leading to emission from only one metal unit. In acetone both RuRuCl and the OsRuCl show photodissociation of the monodentate ruthenium moiety; however, RuOsCl and OsOsCl were found to be photostable.

Journal Article↗

Incorporation of Ru(2)(O(2)C(CH(2))(6)CH(3))(4) into Extended Chains: Interaction of Ru(2)(O(2)C(CH(2))(6)CH(3))(4) with Pyrazine, 4-Cyanopyridine, TCNE, and p-Benzoquinone.

In attempts to form extended chains Ru(2)(O(2)C(CH(2))(6)CH(3))(4) (1) was reacted with both simple coordination and redox-active bridging ligands. The simple coordination ligands, pyrazine (pz) and 4-cyanopyridine (4-cp), coordinated in the axial sites of the diruthenium complex. With the symmetric ligand pyrazine, the polymer [1(pz)](n)() was isolated. With the asymmetric ligand 4-cp, the pyridine nitrogen coordinated preferentially and the bis-adduct 1(4-cp)(2) was isolated. Solution UV/visible and NMR studies indicated that pi-interactions between the Ru-Ru pi and ligand pi orbitals were occurring in both cases. Mole ratio and continuous variation studies of 1 with pyrazine and 4-cp indicated that these axial ligands were labile and that a number of solution species existed. When 1 was reacted with TCNE, redox reactions occurred. Solid-state IR and solution NMR studies also showed that both 1(TCNE) (2) and [1](2)TCNE (3) contained diruthenium carboxylate cores which no longer possessed the D(4)(h)() paddle-wheel geometry. With p-benzoquinone, redox reactions occurred upon coordination to give [1(+)][SQ(-)(*)] (4), which contained an undisrupted oxidized diruthenium tetracarboxylate core. Formation of 4 was reversible in solution, with 1 and p-benzoquinone being favored at higher temperatures.

Journal Article↗

Pyrrolodiazines. 2. Structure and Chemistry of Pyrrolo[1,2-a]pyrazine and 1,3-Dipolar Cycloaddition of Its Azomethine Ylides.

A new synthesis of the pyrrolo[1,2-a]pyrazine system from pyrrole is described. In light of the ab initio calculations carried out on this heterocyclic system some of its basic chemistry was investigated and included electrophilic substitution, addition of organolithium reagents, metalation with lithium diisopropylamide and subsequent reaction with electrophiles, and formation of salts by quaternization of the nonbridgehead nitrogen. N-ylides obtained from these salts undergo 1,3-dipolar cycloaddition with suitable dipolarophiles to give dipyrrolo[1,2-a]pyrazines, pyrazolo[1,5-a]-pyrrolo[2,1-c]pyrazines, and heterobetaines. Examples of intramolecular 1,3-dipolar cycloadditions are also reported.

Journal Article↗

Synthesis and structure of Zn7(mu4-O)2(OAc)10(Pz)2(OAc = acetate; Pz = pyrazine).

Reaction of Zn(OAc)(2).2H(2)O with pyrazine in refluxing ethanol gives the unusual heptanuclear complex Zn7(mu4-O)(2)(OAc)(10)(Pz)(2) (1) (OAc = acetate, Pz = pyrazine) in 46% yield. A single-crystal X-ray diffraction study of revealed a central Zn(7) core in which two pseudo-tetrahedral Zn(4) units are joined at a common vertex. The two pyrazine molecules are bound as terminal (eta1) ligands.

Journal Article↗

A quantum-classical approach to the photoabsorption spectrum of pyrazine.

We have used the time-dependent discrete variable representation (TDDVR) method to simulate the photoabsorption spectrum of pyrazine. The time-dependent molecular dynamics of pyrazine after excitation to the S2 electronic state is considered as a benchmark to investigate the S2 absorption spectrum. We have carried out the dynamics on a basic four-mode model of pyrazine with the inclusion of five major modes as well as the rest of the vibrational modes as bath modes. Investigations reveal the effect of bath modes such as energy and population transfer from the subsystem to the bath. Calculated results demonstrate excellent agreement with traditional quantum-mechanical findings during the entire propagation and converge to the exact quantum results when enough gridpoints are used. It appears that TDDVR, as a numerical quantum dynamics methodology, is a good compromise between accuracy and speed.

Journal Article↗

Poly[copper(II)-mu-pyrazine-mu(3)-squarato].

In the structure of the title compound, [Cu(C(4)O(4))(C(4)H(4)N(2))](n), each copper cation is surrounded by three squarate (3,4-dihydroxy-3-cyclobutene-1,2-dioate) anions and two pyrazine ligands, all of which are located in special positions. The copper cation and all atoms of the squarate anion are located on a mirror plane, whereas the pyrazine ligand is located around a mirror plane which is perpendicular to the ring plane. The cations are connected via the squarate anions and the pyrazine ligands, forming sheets parallel to (001).

Journal Article↗

A pyrazine bis-adduct of a binuclear rhodium(II) carboxylate containing 3,4,5-triethoxybenzoate as the equatorial ligand.

The title compound, tetrakis(mu-3,4,5-triethoxybenzoato-kappa(2)O:O')bis[(pyrazine-kappa N)rhodium(II)](Rh[bond]Rh), [Rh(2)(C(13)H(17)O(5))(4)(C(4)H(4)N(2))(2)], crystallizes on an inversion centre in the triclinic space group P1. The equatorial carboxylate ligands bridge the two Rh(II) atoms, giving a binuclear lantern-like structure. The pyrazine molecules occupy the two axial coordination sites. The phenyl rings are tilted by ca 10 degrees with respect to the attached carboxylate groups. The pyrazine planes have a torsion angle of ca 19 degrees around the Rh-N bond with respect to the plane of the nearer carboxylate group and are not coplanar with the Rh[bond]Rh bond.

Journal Article↗

Crystal engineering using bisphenols: interwoven ladders, sheet and framework structures in the binary adducts of 4,4'-sulfonyldiphenol with pyrazine (2/1), 4,4'-bipyridyl (1/1), trans-1,2-bis(4-pyridyl)ethene (1/1), 1,2-bis(4-pyridyl)ethane (1/1) and 4,4'-trimethylenedipyridine (1/1), and in 4,4'-sulfonyldiphenol-4,4'-trimethylenedipiperidine-water (2/2/1).

The structures of six hydrogen-bonded adducts of 4,4'-sulfonyldiphenol with heteroaromatic amines have been determined. In 4,4'-sulfonyldiphenol-pyrazine (2/1) the pyrazine molecules lie across centres of inversion. The bisphenol molecules are linked into C(8) chains parallel to [100] by means of O-H.O=S hydrogen bonds, and antiparallel pairs of these chains are cross-linked by the pyrazine molecules, via O-H.N hydrogen bonds, to form molecular ladders containing R(6)(6)(50) rings between the rungs of the ladders. Each ladder is interwoven with two neighbouring ladders, thus producing a continuous two-dimensional sheet. The structure of 4,4'-sulfonyldiphenol-4,4'-bipyridyl (1/1) consists of spiral C(2)(2)(21) chains parallel to [010] containing alternating bisphenol and bipyridyl molecules linked by O-H.N hydrogen bonds: these chains are linked by two types of C-H.O hydrogen bonds which form C(5) chains along [001] and C(2)(2)(10) chains along [101], thus generating two interconnected nets characterized in the one case by a chequerboard pattern of R(6)(6)(44) and R(6)(6)(52) rings, and in the other by a single type of R(6)(6)(46) ring. 4,4'-Sulfonyldiphenol-trans-1,2-bis(4-pyridyl)ethene (1/1) [systematic name: 4,4'-sulfonyldiphenol-trans-4,4'-vinylenedipyridine (1/1)] and 4,4'-sulfonyldiphenol-1,2-bis(4-pyridyl)ethane (1/1) [systematic name: 4,4'-sulfonyldiphenol-trans-4,4'-ethylenedipyridine (1/1)] are isomorphous: the 1,2-bis(4-pyridyl)ethene component exhibits orientational disorder, corresponding approximately to a 180 degrees rotation of ca 23% of the molecules about the N.N vector; in each compound the structure is built from C(2)(2)(23) chains of alternating bisphenol and bis(pyridyl) molecules connected by O-H.N hydrogen bonds, running parallel to [112] and generated by translation. The [112] chains are linked by C-H.O hydrogen bonds which generate C(2)(2)(12) chains parallel to [101], so forming a two-dimensional net built from R(6)(6)(50) rings. The structure of 4,4'-sulfonyldiphenol-4,4'-trimethylenedipyridine (1/1) consists of C(2)(2)(24) chains parallel to [100] generated by translation and consisting of alternating bisphenol and bis(pyridyl) molecules linked by O-H.N hydrogen bonds. Pairs of such chains are coiled together to form double helices, and pairs of such double helices, of opposite hand, are linked together by paired C-H.O hydrogen bonds in R(2)(2)(10) rings to form pairs of interwoven ladders in which the C(2)(2)(24) chains form the uprights and the R(2)(2)(10) rings form the rungs, between which are R(6)(6)(50) rings: an R(2)(2)(10) ring belonging to one ladder lies at the centre of an R(6)(6)(50) ring belonging to the other. 4,4'-Sulfonyldiphenol-4,4'-trimethylenedipiperidine-water (2/2/1) is a salt, 2C(13)H(27)N(2)(+).2C(12)H(9)O(4)S(-).H(2)O, containing two independent singly protonated diamine cations, two independent bisphenolate anions, and neutral water molecules. The two independent diamine cations are linked by N-H.N hydrogen bonds into C(2)(2)(24) chains running parallel to [001] and generated by translation, and each type of bisphenolate anion forms an independent spiral C(12) chain, also parallel to [001]. The three types of chain are linked by the water molecules: the two types of bisphenolate chain are linked by water molecules acting as double donors in O-H.O(-) hydrogen bonds in a C(6)(4)(32) chain parallel to [100], thus generating a two-dimensional net built from R(8)(6)(56) rings; the diamine chains are linked to these nets by means of N-H.O hydrogen bonds in which the water molecules act as acceptors and further hydrogen bonds, of N-H.O(-) and N-H.O=S types, link these two-dimensional nets into a continuous three-dimensional framework.

Journal Article↗