Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Pyrones”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34Linked to original sources
PubMed2004

Efficient Baylis-Hillman reactions of cyclic enones in methanol as catalyzed by methoxide anion.

The Baylis-Hillman reactions of cyclic enones with a variety of aldehydes were investigated. 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) was found to be a viable catalyst in promoting the reactions of sterically retarded substrates in methanol. The reactions showed clear solvent dependence and only occurred in hydroxylic solvents, especially in methanol. Further consideration on the steric character of DBU and its high basicity jointly with other experimental observations suggests that the methoxide anion should be the "true" Baylis-Hillman catalyst. This has been confirmed by the effectiveness of similar reactions directly employing methoxide as the catalyst. The reaction pathways of this type of catalysis are proposed to depend on the choice of substrates. Supporting experimental observations were demonstrated and discussed in relation to mechanistic considerations. This study also reveals that both DBU and sodium methoxide can be successfully applied as effective catalysts in methanol to promote the Baylis-Hillman reactions for a range of cyclic enones including cyclopent-2-enones, cyclohex-2-enones, gamma-pyrone, and 1-benzopyran-4(4H)-ones.

Journal Article↗
PubMed2005

On the pyrolysis mechanism of 2-pyranones and 2-pyranthiones: thermally induced ground electronic state chemistry of pyran-2-thione.

[reaction: see text] This work reports studies of thermochemistry of pyran-2-thione (PT), a sulfur derivative of alpha-pyrone (AP). Moderate heating of PT results in scrambling of sulfur and oxygen atoms in the molecule and formation of isomeric thiapyran-2-one (TP). The products of pyrolysis of PT were studied experimentally by a combined use low temperature matrix isolation and Fourier transform infrared spectroscopy. The infrared spectrum of the TP monomer isolated in solid argon at 10 K was completely assigned based on comparison with theoretical calculations undertaken at the DFT(B3LYP)/6-311++G(d,p) level. The upper limit of thermal stability of PT was investigated using the differential scanning calorimetry technique. It was found that pyrolysis of PT is already initiated at temperatures below 130 degrees C. The mechanism of the observed pyrolytical conversion has been studied theoretically at the MP2/6-311++G(d,p) level, in the ground electronic state. The primary step of the pyrolytical reaction in PT is the alpha-cleavage of the C-O single bond. It proceeds via an open-ring thioketene-aldehyde structure, TK1. According to the calculations, the ring-opening reaction from PT to TK1 requires an activation energy less than 80 kJ mol(-1), at 130 degrees C, being the rate-determining step. Further steps of the pyrolytical reaction involve internal rotations around single bonds and [1,5] sigmatropic shift of the aldehydic hydrogen. Pyrolytical ring-opening reactions were studied theoretically also for AP and TP and compared to the pyrolysis of PT. It is suggested that the relative ease of the pyrolytical transformation in PT can be explained in terms of existence of the additional minimum TK1 in the reaction path. No counterparts for this structure could be theoretically located for AP and TP.

Journal Article↗
PubMed2006

Berkelic acid, a novel spiroketal with selective anticancer activity from an acid mine waste fungal extremophile.

Berkeley Pit Lake is an abandoned open-pit copper mine filled with 30 billion gallons of acidic, metal-contaminated water. This harsh environment is proving to be a source of unusual microorganisms that produce novel bioactive metabolites. Bioassay-guided fractionation using signal transduction enzyme assays led to the isolation of the novel spiroketal, berkelic acid 1, and of the known gamma-pyrone, spiciferone A 4. Berkelic acid has shown selective, nanomolar activity against OVCAR-3, an ovarian cancer cell line in the National Cancer Institute cell line screen. The isolation and characterization of these compounds are reported here.

Antineoplastic Agents↗
PubMed1997

Site-Selective Diels-Alder Reactions of 7-(Methoxyimino)-4-methylchromene-2,8-dione with Alkenes.

Regio- and site-selective Diels-Alder reactions of o-quinone monooxime 1 are reported. The electron rich dienophiles 2, 4, 6, 8, and 10 react with the exocyclic diene system of monooxime 1 leading to the coumarin derivatives 3, 5, 7, 9, 11, and 12. The electron deficient dienophiles 13a,b and 18 react with the quinoid and the pyrone diene systems of compound 1 affording the cycloadducts 14a,b, 17a,b, and 19.

Journal Article↗
PubMed1997

Antiproliferative Hybrid Analogs of the Hormone 1alpha,25-Dihydroxyvitamin D(3): Design, Synthesis, and Preliminary Biological Evaluation.

The combination of 10-12 kbar pressure plus Lewis acidic zinc dichloride promotes highly regioselective and stereoselective Diels-Alder cycloaddition between 3-bromo-2-pyrone, prepared in a new way, and unactivated terminal alkene 4-(tert-butyldimethylsiloxy)-1-butene. The conjugate base of A-ring allylic phosphine oxide 20 adds chemospecifically to the C-8 keto group of some C-8,C-24-diketones to form directly metabolically resistant 24-oxo analogs of 1alpha,25-dihydroxyvitamin D(3) (calcitriol). Several of these new hybrid analogs are as efficacious in vitro as calcitriol at inhibiting growth of murine keratinocytes even at physiologically relevant 10-100 nanomolar concentrations.

Journal Article↗
PubMed1999

Straightforward Construction of Fused 6,7,5-Tricarbocyclic Systems by Tandem [5 + 2]/[4 + 2] Cycloadditions.

One-pot coupling of an intramolecular thermal [5C + 2C] pyrone-alkene cycloaddition to a [4C + 2C] Diels-Alder reaction provides immediate access to 6,7,5-tricarbocyclic systems bearing a 1,4-oxa-bridge in the seven-membered carbocycle. The transformation entails the net formation of four carbon-carbon bonds and creates three new cycles and a minimum of five new stereocenters. Preliminary attempts to open the oxa-bridge by reaction of the adducts with samarium diiodide and trimethylsilyl triflate led to relatively unexpected deoxygenated and aromatized products.

Journal Article↗
PubMed2000

A facile and convenient synthesis of 3-alkylamino-5-arylthiophenes with a variety of substituents at C-2 and studies of reaction mechanisms

Thioaroylketene S,N-acetals were treated with active methylene compounds including beta-keto ester, nitromethane, cyanoacetic acid, p-toluenesulfonylacetone, 4-nitrophenylacetic acid, and diethyl (2-oxopropyl)phosphonate in the presence of mercury(II) acetate in CH(2)Cl(2) at room temperature. These reactions gave 3-alkylamino-5-arylthiophenes containing various substituents, which comprised, respectively, alkoxycarbonyl, nitro, cyano, p-toluenesulfonyl, 4-nitrophenyl, and diethylphosphono groups at C-2 in good yields. The reaction of 3-methylamino-3-methylthio-1-phenylthioxopropene with malonic acid or Meldrum's acid under the same conditions gave 3-methylamino-5-phenylthiophene. Similarly, treatment of 3-methylamino-3-methylthio-1-phenylthioxopropene with various enolizable cyclic ketones such as 4-hydroxy-6-methyl-2-pyrone, homophthalic anhydride, 2-hydroxy-1,4-benzoquinone, and 1, 3-diethyl-2-thiobarbituric acid gave thieno[3,2-b]pyridin-4-one, thieno[3,2-c]isoquinolin-5-one, thieno[3,2-c]benzazepine-1,6-dione, and thieno[3,2-d]pyrimidine-2,4-dione, respectively.

Journal Article↗
PubMed2001

New acetophenone glucosides isolated from extracts of Helichrysum italicum with antiinflammatory activity.

Three new acetophenone glucosides (4-6), three known aglycons (1-3), and a benzo-gamma-pyrone glucoside (7) were isolated from the CH(2)Cl(2), EtOAc, and BuOH extracts from the aerial parts of Helichrysum italicum. All the compounds tested showed antiinflammatory activity in a 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced mouse ear edema test, and the ID(50) value of compound 2, the most active compound, was determined.

Acetophenones↗
PubMed2002

New metabolites from sponge-derived fungi Curvularia lunata and Cladosporium herbarum.

The fungus Curvularia lunata, isolated from the marine sponge Niphates olemda, yielded the new 1,3,8-trihydroxy-6-methoxyanthraquinone, which we named lunatin (1), the known modified bisanthraquinone cytoskyrin A (2), and the known plant hormone (+)-abscisic acid (3). Both anthraquinones were found to be active against Bacillus subtilis, Staphylococcus aureus, and Escherichia coli. Two strains of the fungus Cladosporium herbarum, isolated from the sponges Aplysina aerophoba and Callyspongia aerizusa, respectively, yielded two new alpha-pyrones, herbarin A (4) and herbarin B (5), the known compound citreoviridin A (6), and the new phthalide herbaric acid (7). All structures were unambiguously established by 1D and 2D NMR and MS data.

Abscisic Acid↗
PubMed2002

Isolation and structure of a 20,21-epoxybufenolide series from "Ch'an Su".

Steroid bufenolides resulting from epoxidation of the 17beta-2-pyrone ring of bufadienolides are rare. Five 20,21-epoxybufenolides, namely, 20S,21-epoxyresibufogenin (1), 20R,21-epoxyresibufogenin (2), 3-O-formyl-20S,21-epoxyresibufogenin (3), 3-O-formyl-20R,21-epoxyresibufogenin (4), and 3-oxo-20S,21-epoxyresibufogenin (5), were isolated from the Chinese toad skin extract drug Ch'an Su. The structures were elucidated by spectroscopic and chemical methods. The configuration at C-20 was assigned by the analysis of difference NOE spectra. The cancer cell (KB and MH-60) growth inhibition by the new 20,21-epoxybufenolides was examined, and 20,21-epoxides 1, 2, and 5 were found to significantly inhibit the leukemia MH-60 cell line.

Animals↗
PubMed2005

Koniamborine, the first pyrano[3,2-b]indole alkaloid and other secondary metabolites from Boronella koniambiensis.

Two new alkaloids, (-)-cis-1,2-dihydroxy-1,2-dihydromedicosmine (3) and koniamborine (4), have been isolated from Boronella koniambiensis aerial parts. Their structures have been established from NMR and mass data. Koniamborine is a novel type of alkaloid, which derives from the pyrano[3,2-b]indole basic skeleton, described for the first time from nature. 6-Methoxy-1-methylisatin, also present in the plant material, can be considered biogenetically as a degradation product of the fused pyrone ring of 4.

Heterocyclic Compounds, 4 or More Rings↗
PubMed1992

Inhibitory effects of flavonoids on Moloney murine leukemia virus reverse transcriptase activity.

Several flavonoids were tested for their effects on Moloney murine leukemia virus reverse transcriptase activity. Four groups of flavonoids, namely flavones, flavanones, flavonols, and flavanonols, were studied, and it was found that flavonols and flavanonols were very active in this regard while flavones and flavanones displayed very low activity. Among the flavonoids tested, fisetin, quercetin, myricetin, kaempferol, morin, (+/-)-taxifolin, (+)-catechin, and (-)-epicatechin were shown to be highly effective in inhibiting the reverse transcriptase activity. Structure-activity relationship analysis of these flavonoids revealed that the simultaneous presence of free hydroxyl groups at positions 3 and 4' enhanced the reverse transcriptase inhibitory activity. Replacement of the 3-hydroxyl group with a monosaccharide or of the 4'-hydroxyl group with a methyl group reduced inhibitory activity. The double bond at position 2 and 3 of the flavonoid's pyrone ring is not essential for inhibiting reverse transcriptase activity. The flavonoids studied demonstrated ability to inhibit the reverse transcriptase activity using either (rA)n(dT)12-18 or (rC)n(dG)12-18 as template-primers.

DNA Polymerase I↗
PubMed1995

Acetylcholinesterase inhibition by territrem B derivatives.

Five derivatives of territrem B [2], a potent acetylcholinesterase inhibitor isolated from a rice culture of Aspergillus terreus, were prepared from 2 as well as from its major metabolite, 4 beta-hydroxymethyl-4 beta-demethylterritrem B [4]. The inhibitory activities of these derivatives against electric eel acetylcholinesterase (E.C. 3.1.1.7) were tested and it was concluded that the enone and the pyrone groups present in 2 may play an important biological role.

Animals↗
PubMed2000

Sulfinyl-directed diastereoselective

Introduction of a homochiral p-tolylsulfinyl group at an appropriate position in the alkene accelerates the thermal [5C + 2C] intramolecular cycloaddition to beta-silyloxy-gamma-pyrones and, most importantly, leads to excellent levels of diastereodifferentiation. The resulting adducts can be easily desulfinylated to give optically active 8-oxabicyclic[3.2.1]octane intermediates which by virtue of their rich functionalization might be susceptible to elaboration into enantiomerically pure natural products containing seven-membered carbocycles and tetrahydrofurans.

Journal Article↗
PubMed2000

Radical-initiated, skeletal rearrangements of Bicyclo

Treatment of bicyclic lactones derived from Diels-Alder reactions of 3-carbomethoxy-2-pyrone under radical conditions leads to a series of interesting skeletal rearrangements. The stereochemical and optical integrity of the starting material are maintained throughout the process.

Journal Article↗
PubMed2000

Hetero Diels-Alder reactions of 1-amino-3-siloxy-1,3-butadienes under strictly thermal conditions.

The hetero Diels-Alder reaction of 1-amino-3-siloxy-1,3-butadiene (1a) with a range of unactivated aldehydes proceeds readily under remarkably mild conditions: at room temperature and in the absence of Lewis acid catalysts. The cycloadducts are formed in good yields and can be converted directly to the corresponding dihydro-4-pyrones using acetyl chloride. Ketones and imines are also reactive in hetero Diels-Alder reactions with this diene.

Butadienes↗
PubMed2001

Unusual influence of substituents on ring-opening metathesis reactions.

The ring-opening cross-metathesis of oxabicyclo[3.2.1]octene derivatives provides a convenient method for preparing differentially substituted 4-pyrones. The major competing reaction is the ring-opening metathesis polymerization of the bridged olefin. Studies on this reaction have shown that substituents on the bicyclic alkene can have a dramatic influence on the competing reactions. [reaction: see text]

Journal Article↗