Pyrylium Research Articles

New Approach for Fluorescent Peptide Labeling with Pyrylium Cyanine Dyes

New approach for fluorescent peptide labeling with cyanine dyes utilizing the reaction of pyrylium salts with aliphatic aminogroup is proposed. The reaction of two pyrylium cyanines dye acids was investigated. Lysocyme was used as a model peptide for conjugation. The proposed method can be used as a simple and convenient alternative for the known procedures because it does not require preparation of the unstable amino-reactive intermediates from a carboxyl- or sulfo-derivative of cyanine dyes.

Carbonic anhydrase activators: design of high affinity isozymes I, II, and IV activators, incorporating tri-/tetrasubstituted-pyridinium-azole moieties.

A series of tight binding carbonic anhydrase (CA) activators was obtained by reaction of amino-azoles (3-amino-pyrazole, 2-amino-imidazole, and 5-amino-tetrazole) with tri- or tetrasubstituted pyrylium salts. Many of the new pyridinium salts incorporating azole moieties reported here proved to be efficient in vitro activators of three CA isozymes, CA I, II, and IV. Very good activity was detected against hCA I and bCA IV (h = human; b = bovine isozymes), for which some of the new compounds showed affinities in the low nanomolar range, whereas against hCA II, their affinities were in the range of 95-150 nM. Substitution patterns of the pyridinium ring leading to best activity included 4-phenyl-2,6-dialkyl moieties or 2,4,6-tri- and 2,3,4,6-tetraalkyl groups. Ex vivo experiments showed some of the new activators to strongly enhance CA activity after incubation with human erythrocytes. Furthermore, due to their cationic nature, some of these compounds (the imidazole and pyrazole derivatives) are membrane-impermeant, discriminating thus between cytosolic and membrane-bound CA isozymes. The present paper is the first report of membrane-impermeant CA activators. The pyridinium tetrazole derivatives on the other hand do penetrate through biological membranes. Such CA activators might lead to the development of drugs/diagnostic tools for the management of CA deficiency syndromes as well as for the pharmacological enhancement of synaptic efficacy, spatial learning, and memory. This may constitute a new approach for the treatment of Alzheimer disease and other conditions in need of achieving memory therapy.

ChemInform Abstract: Reactions of Pyrylium Salts with Nucleophiles. Part 26. The Reaction with the Cyanide Anion Revisited.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The photochemistry of pyrylium salts: new photohydrations and photoamidations of heterocycles leading to bicyclic oxazolines and functionalized cyclopentenes.

The photochemistry of pyrylium salts: new photohydrations and photoamidations of heterocycles leading to bicyclic oxazolines and functionalized cyclopentenes.

Abatement of the major contaminants present in olive oil industry wastewaters by different oxidation methods: ozone and/or UV radiation versus solar light

Four different cinnamic acids (caffeic acid, ferulic acid, p-coumaric acid and cinnamic acid) present in olive oil wastewaters, were treated with advanced oxidation methods: ozone and/or UV radiation. Basic and acid media were tested. Differences between all four acids were found, both in the reaction times and the intermediates formed. Based on a careful study of these intermediates and the variation of their concentrations all along the reaction time, a general mechanism for the degradative oxidation of cinnamic acids is proposed. These results are compared with those obtained with solar light, using a pyrylium salt as a catalyst.

Cyclic transmembrane charge transport mediated by pyrylium and thiopyrylium ions.

Transient spectroscopy revealed that 2,4,6-trimethylpyrylium, 2,4,6-triphenylpyrylium, and 2,4,6-triphenylthiopyrylium ions oxidatively quench excited triplet [5,10,15,20-tetrakis(4-sulfonatophenyl)porphinato]zinc(II) to form the corresponding neutral radicals and the zinc porphyrin pi-cation. The measured quenching rate constants were proportional to the pyrylium one-electron reduction potentials, that is, the reaction driving force. In the presence of anionic dihexadecyl phosphate vesicles, only the fraction of pyrylium not bound to the vesicle was capable of reacting with the photoexcited zinc porphyrin. Nonetheless, the pyrylium radicals mediated highly efficient transmembrane reduction of tris(2,2'-bipyridine)cobalt(III) contained within the inner aqueous core of the vesicles with apparent quantum yields that approached unity. Permeability coefficients (P) determined for the pyrylium radicals, pyrylium cations, and the proton were 10(-4)-2 x 10(-5) cm/s, 10(-10) cm/s, and < 5 x 10(-7) cm/s, respectively, so that only the neutral radicals are membrane-permeable on the time scale of the transmembrane redox reactions. However, each electron carrier was demonstrated to transport up to 200 electrons, at which point the internal pool of electron acceptors was exhausted. Since the cations are membrane-impermeable, a reaction cycle is proposed that includes hydrolysis of the pyrylium cations formed within the aqueous core to the corresponding 1,5-diketones which, as neutral molecules, can diffuse across the bilayer. According to this mechanism, while undergoing redox cycling the pyrylium ions function as cyclical antiporters of OH(-) and the electron, thereby maintaining electroneutrality in the reaction compartments.

Phosphabenzenes as monodentate pi-acceptor ligands for rhodium-catalyzed hydroformylation.

A new class of phosphinine/rhodium catalysts for the hydroformylation of terminal and internal alkenes is presented in this study. A series of phosphabenzenes 1-14 has been prepared by condensation of phosphane or tris(trimethylsilyl)phosphane with the corresponding pyrylium salt. Trans-[(phosphabenzene)2RhCl(CO)] complexes 21-25 have been prepared and studied spectroscopically and by X-ray crystal-structure analysis. The hydroformylation of oct-1-ene has been used to identify optimal catalyst preformation and reaction conditions. Hydroformylation studies with 15 monophosphabenzenes have been performed. The catalytic performance is dominated by steric influences, with the phosphabenzene 8/rhodium system being the most active catalyst. Turnover frequencies of up to 45370 h(-1) for the hydroformylation of oct-1-ene have been determined. In further studies, hydroformylation activity toward more highly substituted alkenes was investigated and compared with the standard industrial triphenylphosphane/rhodium catalyst. The reactivity differences between the phosphabenzene and the triphenylphosphane catalyst increase on going to the more highly substituted alkenes. Even tetrasubstituted alkenes reacted with the phosphabenzene catalyst, whereas the triphenylphosphane system failed to give any product. In situ pressure NMR experiments have been performed to identify the resting state of the catalyst. A monophosphabenzene complex [(phosphinine 8)Ir(CO)3H] could be detected as the predominant catalyst resting state.

Interaction of cyanine dyes with nucleic acids — XXVII: synthesis and spectral properties of novel homodi- and homotrimeric monomethine cyanine dyes

Three new methods of preparation based on reactions of pyrylium salts with primary amines, acylation of polyamines with activated carboxyl derivatives of cyanine dyes, diisocyanate with aminoderivatives of cyanine dyes were used to obtain fluorescent homodi- and, for the first time, homotrimer cyanine dyes. Spectral-luminescent properties of synthesized dyes and their nucleic acid complexes were studied.

Steady-state and time-resolved studies on oxetane cycloreversion using (thia)pyrylium salts as electron-transfer photosensitizers.

[reaction: see text] Cycloreversion of oxetane 1 is achieved using (thia)pyrylium salts as photosensitizers. RadicaI cation intermediates involved in the electron-transfer process have been detected using laser flash photolysis. The experimental results are consistent with the reaction taking place from the triplet excited state of the sensitizer.

Poly(pyridinium salt)s with stilbene or distyrylbenzene chromophores

AbstractA new series of poly(pyridinium salt)s that contained side stilbenyl groups or p‐distirylbenzene segments in the main chain were synthesized from the reactions of bis(pyrylium salts) with diamines. They were characterized by viscometry, Fourier transform infrared spectroscopy, NMR, X‐ray scattering, differential scanning calorimetry, thermomechanical analysis, ultraviolet–visible analysis, and luminescence spectroscopy. The polymers were amorphous and soluble in polar aprotic solvents such as dimethylacetamide, dimethylformamide, and dimethyl sulfoxide. The glass‐transition temperatures were in the range of 59–123 °C. These polymers had initial decomposition temperatures of 240–295 °C and afforded anaerobic char yields of 29–53% at 800 °C. Both the absorption and photoluminescence (PL) spectra of the polymers were studied, and the PL quantum yields in solution were determined. The polymers showed violet‐blue fluorescence in solution with PL maxima at 408–416 nm and violet‐green fluorescence in thin film with PL maxima at 454–523 nm. The structure of the diamine utilized for the preparation of the polymers did not influence their PL maxima. © 2001 John Wiley &amp; Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2454–2462, 2001

Взаємодія ціанінових барвників з нуклеїновими кислотами. 22. Спектрально-люмінесцентні властивості монометинових пірилієвих і піридинових ціанінів та їхніх комплексів з ДНК

Взаємодія ціанінових барвників з нуклеїновими кислотами. 22. Спектрально-люмінесцентні властивості монометинових пірилієвих і піридинових ціанінів та їхніх комплексів з ДНК

Reactions of Pyrylium Salts with Nucleophiles. Part 26.1 the Reaction with the Cyanide Anion Revisited

Reaction mechanisms are provided for the formation of diastereomeric 2,4-dialkyl-6-oxo-2,4-heptadienonitriles (including minor diastereoisomers observed for the first time) from 2,4,6-trialkylpyrylium salts and aqueous sodium cyanide.

On triazoles XLIII. Synthesis of 1,2,4‐triazolyl isoquinolinium zwitter ions

AbstractType 8 isoquinolinium zwitter ions were synthesised by the reaction of type 1 diketones or type 2 pyrylium salts with different 5‐amino‐3‐Q‐1H‐1,2,4‐triazoles. Spectroscopic and X‐ray diffraction evidence was given for the zwitter ion structure of the products obtained. The position of the negative charge on the 1,2,4‐tiazolium ring was proved by comparison of the cmr and uv spectra of the products obtained with the three possible N‐benzyl derivatives 14–16 prepared for this purpose.

Pyrylium salt-photosensitised degradation of phenolic contaminants present in olive oil wastewaters with solar light: Part II. Benzoic acid derivatives

Solar light photodegradation, catalysed by a pyrylium salt, of seven benzoic acids present in olive oil mill, has been studied. Significant percentages of photodegradation (20–40%) have been achieved after 6h of solar exposure for six of the acids, even though they were expected to be difficult to oxidise, due to the presence of an electron-withdrawing carboxylic acid group directly attached to the aromatic ring. Quenching constants for the electron-transfer process between the substrate and the excited catalyst were calculated by means of fluorescence measurements for syringic acid (66×109M−1s−1), gallic acid (51×109M−1s−1), veratric acid (51×109M−1s−1), vanillic acid (48×109M−1s−1), protocatechuic acid (37×109M−1s−1) and p-hydroxybenzoic acid (15×109M−1s−1); no quenching was found for benzoic acid. These photophysical measurements are in good correlation with the yields obtained in the pyrylium salt photocatalysed degradation of those phenolic acids.

Photochemical Single-Crystal-To-Single-Crystal Dimerizations and Polymerizations

Single-crystal-to-single-crystal reactions of a series of bifunctional styrylyl]pyrylium salts have been investigated using long wavelength irradiation conditions. The dimerization of the reactive olefins in the solid state was followed by X-ray crystallography. The results demonstrate that a homogeneous photoreaction occurred under topochemical control. Two systems which can be polymerized in the solid-state are described.

Stereoselective Multiple Functionalization of Pyrylium Salts by Domino Reactions with 2-Silyloxybuta-1,3-dienes.

Six at a time! Up to six stereogenic centers can be diastereoselectively formed in one step in three-component domino reactions of 4-silyloxypyrylium triflates with 2-silyloxybuta-1,3-dienes. Annulated or bridged ring systems such as 1 and 2, respectively, can be formed with high selectivity. R1 =silyl group; R2 , R3 =organyl group.

ChemInform Abstract: Ring Transformations of Heterocyclic Compounds. Part 20. Benzo‐fused Spiro[cyclohexadiene‐dihydroindoles] by Ring Transformation of Pyrylium Salts with Anhydrobases of Benzo[e]‐ and Benzo[g]indolium Salts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

CATALYTIC REDUCTION OF PYRIDINIUM, PYRYLIUM, AND THIOPYRYLIUM SALTS. (REVIEW)

Published data and the results of the authors' own investigations on the synthesis of six-membered saturated N-, O-, and S-containing heterocycles by catalytic reduction of pyridinium, pyrylium, and thiopyrylium salts are reviewed. The conditions, laws, and special characteristics of the reactions are considered.

Photoinduced electron‐transfer reaction of cyclic oligosilanes and polysilanes in solution

AbstractPhotoinduced electron‐transfer (PET) reactions were investigated for the cyclic oligosilanes and high molecular weight polysilanes in the presence of 9‐cyanoanthracene (CA), 9,10‐dicyanoanthracene (DCA), and triphenylpyrylium tetrafluoroborate (TPP+BF) using chemical and spectroscopic methods in solution. For the cyclic oligosilanes, the pyranyl radical (TPP·) and silane radical cation were observed as direct evidence of the PET from silanes to TPP+BF, and the reaction quantum yields showed that the ring opening of the radical cation of the cyclic oligosilane competed with the nucleophilic attack on the radical cation by the counter ion of the pyrylium salt and a back electron transfer (BET). For the high molecular weight polysilane, the observation of the transient absorptions of TPP· and the radical cation of polysilane is evidence of the PET, and the extremely long lifetime observed for the radical cation indicates the inefficient BET and reactivities. © 2001 John Wiley &amp; Sons, Inc. Heteroatom Chem 12:269–275, 2001

Spirobipyridopyrans and indolinospiropyridopyrans: Synthesis, X-ray crystal structure, separation of enantiomers, and barriers to thermal cleavage of the C(sp(3))-O bond.

The novel chiral spirobipyridopyrans 1 and 2 were synthesized by the acid catalyzed aldol type condensation of 5-deoxypyridoxal with the appropriate ketone and subsequent reaction of the resulting pyrylium salt with base. The indolinospiropyridopyrans 3-5, which contain the modified B(6) unit, were prepared by aldol reaction of 5-deoxypyridoxal with 1,3,3-trimethyl-2-methylenindolines. Analytical separation of enantiomers was accomplished by low-pressure liquid chromatography (LPLC) on triacetylcellulose. The barriers to thermal racemization were determined by on-line measurements of the enriched enantiomers after LPLC. Gibbs energies of activation DeltaG superset, not equals for reversible cleavage of the C(spiro)-O bond in 1, 3, and 4 were in the range 103-108 kJ/mol. The lower limits of the barriers in 2 and 5 were estimated to be greater than 102 and 109 kJ/mol by attempted thermal racemizations. The increase of the barriers from 3 to 4 and 5 was explained by the influence of electron withdrawing groups, which reduce the stability of the ring-opened transition states to C(sp3)-O bond cleavage. Geometrical data from X-ray structure analysis showed that the angle [C3-C2-C3'] around the spiro carbon atom increases with elongation of the chain in the C3-C3' bridge. This angle widening is explained by a ring-strain effect, which is greater in the five-membered ring in the skeleton of 7 than in the six- and seven-membered rings of 1 and 2.