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At least 19 recordsLinked to original sources
PubMed2000

An adjacent thioester provides apical-directed stabilization to 3-isothiazolidinone 1-oxide heterocycles.

The structural and energetic features of the attractive intramolecular through-space S-X interaction [X being oxygen (O) or sulfur (S)] of thioester containing 3-isothiazolidinone 1-oxide heterocycles are described. Density functional theoretical and semiempirical calculations are used to explain the previous X-ray data on 3-isothiazolidinone 1-oxides 5 and 6 [Kanda, Y., Ashizawa, T. , Kakita, S., Takahashi, Y., Kono, M., Yoshida, M., Saitoh, Y., and Okabe, M. (1999) J. Med. Chem. 42, 1330-1332] and implicate a mechanism where the adjacent thioester participates in an apical-directed stabilization of the sulfur heterocycle. A key factor that distinguishes the S-O interaction from the S-S interaction is the stronger through-space interaction of the former, which is a consequence of the greater electronegativity of apical O compared to apical S. Reaction field theory reveals that the conversion of the S-O interaction to the S-S interaction is more facile compared to gas phase computations, which suggest a reduced importance of the 1,5-S-X interactions in solution. The conversion of the S-O interaction to the S-S interaction gives an isothiazolidinone oxide that places the reacting sulfurs in proximity with an orientation presumably suitable for bond formation and access to the dithiolanone oxide surface. Factors that influence the through-space S-X interactions may represent important issues in identifying target 3-isothiazolidinone 1-oxide prodrugs capable of rearranging to 1,2-dithiolan-3-one 1-oxide drugs.

Antibiotics, Antineoplastic↗
PubMed2003

Complexes of Schiff bases and intermediates in the copper-catalyzed oxidative heterocyclization by atmospheric oxygen.

After complexation with copper(II) ions, Schiff bases 1a-d may undergo an oxidative ring closure using atmospheric oxygen to give a number of imidazo[1,5-a]pyridines 2, an imidazo[1,5-a]imidazole 3, and an imidazo[5,1-a]isochinoline 4. This ligand oxidation can be performed with catalytic amounts of copper ions in the reaction. A catalytic cycle for the copper-catalyzed oxidative heterocyclization will be presented together with isolated copper complexes of Schiff bases 1a,b and intermediates 5 and 8 that were found by X-ray structure analyses which confirm this reaction scheme.

Catalysis↗
PubMed1998

Anti-bacterial activity of synthetic N-heterocyclic oxidizing compounds.

Synthetic chlorochromate derivatives of pyridine and quinoline were active in vitro against type cultures of Escherichia coli (ATCC 128), Staphylococcus aureus (ATCC 14775), Pseudomonas aeruginosa (ATCC 10145) and Bacillus subtilis (NCTC 8236). The minimum inhibitory concentrations (MIC) were 125-250 micrograms ml-1 and 250-500 micrograms ml-1 for pyridinium chlorochromate and quinolinium chlorochromate, respectively. An established derivative of quinoline (Perfloxacin) had an MIC of 125-250 micrograms ml-1. The extinction time for 10(5) cfu in broth was 90 min for pyridinium chlorochromate and 120 min for quinolinium chlorochromate, except for B. subtilis which survived up to about 180 min and 360 min. A combination of the two compounds produced an antagonistic effect. The 50% lethal dose (LD50 toxicity) in mice was estimated at 76 micrograms g-1 and 33 micrograms g-1 body weight for the quinolinium and pyridinium chlorochromates. The compounds also exhibited some potential for suppressing a simulated staphylococcal infection in mice at the dosage levels of ca 22 micrograms g-1 for pyridinium chlorochromate and 45 micrograms g-1 for quinolinium chlorochromate.

Animals↗
PubMed2001

Novel small organo-P-S/Se heterocycles.

Oxidative addition of elemental sulfur and selenium to cyclomonocarbatetraphosphines (PhP)4CR2 (R = H, Me) afforded novel five- and four-membered heterocycles PhP(E)CH2PhP(E)E2(E = S, Se) and PhP(Se)CMe2-PhP(Se)Se.

Journal Article↗
PubMedDate not supplied

[Oxidation of phenazepam in isolated hepatocytes from white rats].

In isolated rat hepatocytes aromatic hydroxylation and oxidation of the 14C-phenazepame heterocycle were studied. Both these reactions proceeded with the linear rate in intact hepatocytes and aromatic hydroxylation predominated. After induction of cytochrome P-450 by phenobarbital the rate of the heterocycle oxidation was increased 3.6-fold. Rates of aromatic hydroxylation and the phenazepame heterocycle oxidation did not depend on administration of phenobarbital and 3-methyl cholanthrene into the animals. Effects of the factors studied (concentration of phenazepame, induction of cytochrome P-450 by means of phenobarbital and 3-methyl cholanthrene) on alterations in the rate of oxidation of both aromatic nuclei and the phenazepame heterocycle were estimated using dispersion analysis.

Animals↗
PubMed2005

Synergistic substrates determination with biosensors.

High sensitive biosensors for heterocyclic compounds determination were built using oxidases-catalyzed hexacyanoferrate(III) reduction in the presence of these compounds. As oxidases Aspergillus niger glucose oxidase and recombinant Microdochium nivale carbohydrate oxidase were used. The biosensors were build using graphite electrodes and entrapped solution of the oxidases. The sensitivity of the biosensors achieves 5.2-14.5 microA microM-1 cm-2. The detection limit of some heterocyclic compounds was 0.2 microM. The sensitivity of biosensors was 300-10,000 times larger in comparison to hexacyanoferrate(III). To background the scheme of biosensors action kinetics of synergistic substrates oxidation was investigated in homogenous solution. The measurements showed that the rate of the reduction of low reactive substrate (hexacyanoferrate(III)) increased due to synergistic action of high reactive substrates (oxidized heterocyclic compounds). The modeling revealed the limiting step of the process. The increase of hexacyanoferrate(III) reduction rate is determined by the rate of reduced enzymes interaction with oxidized heterocyclic compound. The oxidation of heterocyclic compounds (mediators) with hexacyanoferrate(III) does not limit the process. The analysis of macrokinetics of biosensors action showed that synergistic effect may be realized and high biosensors sensitivity may be achieved if diffusion module of the enzyme reaction with the oxidized mediator and of a cross reaction is larger than 0.5. The calculated relative sensitivity is about three times higher in comparison to experimentally determined that may be caused by the limited stability of oxidized heterocyclic compounds and/or some external diffusion limitation of substrates.

Aspergillus niger↗
PubMed2004

Oxidation of heterocyclic and aromatic aldehydes to the corresponding carboxylic acids by Acetobacter and Serratia strains.

Conversion of heterocyclic and aromatic aldehydes to the corresponding carboxylic acids was carried out using Acetobacter rancens IFO3297, A. pasteurianus IFO13753 and Serratia liquefaciens LF14. IFO3297 produced 110 g 2-furoic acid l(-1) from furfural with a 95% molar yield. 5-Hydroxymethyl-2-furancarboxylic acid was produced from the corresponding aldehyde by using whole cells LF14. IFO13753 and LF14 both converted isophthalaldehyde, 2,5-furandicarbaldehyde, 2,5-thiophenedicarbaldehyde and 2,2' biphenyldicarbaldehyde to the corresponding formylcarboxylic acid with 86-91% molar yields.

Acetobacter↗
PubMed2004

Functionalized spiro- and fused-ring heterocycles via oxidative demetalation of cyclohexadienyl ruthenium complexes.

Electron-rich alkoxy- and chloro-substituted azaspirocyclic cyclohexadienyl Ru(II) complexes have been converted to either azaspiro[4.5]decane derivatives or functionalized tetrahydroisoquinolines by treatment with suitable oxidizing agents. Copper(II) chloride was found to provide demetalated products in high yield relative to the other oxidants examined (FeCl(3), DDQ, CAN, [Cp(2)Fe][PF(6)], phenyliodine diacetate, IBX). In certain instances, the efficiency of oxidative demetalation was enhanced by the inclusion of chloride ion additives in the reaction. Pyridinium dichromate (PDC) was also found to effect the demetalation of a wide range of cyclohexadienyl Ru complexes; however, isolated yields of metal-free products were exceedingly low. The cyclohexadienyl ruthenium complexes used in this study were prepared from (arene)Ru(II) precursors; thus, the isolation of alicyclic cyclohexadienone derivatives upon demetalation constitutes completion of a Ru-mediated dearomatization process.

Aza Compounds↗
PubMed2002

Activation of leinamycin by thiols: a theoretical study.

Reaction of thiols with the 1,2-dithiolan-3-one 1-oxide heterocycle found in leinamycin (1) results in the conversion of this antitumor antibiotic to a DNA-alkylating episulfonium ion (5). While the products formed in this reaction have been rationalized by a mechanism involving initial attack of thiol on the central sulfenyl sulfur (S2') of the 1,2-dithiolan-3-one 1-oxide ring, the carbonyl carbon (C3') and the sulfinyl sulfur (S1') of this heterocycle are also expected to be electrophilic. Therefore, it is important to consider whether nucleophilic attack of thiol at these sites might contribute either to destruction of the antibiotic or conversion to its episulfonium ion form. To address this question, we have used computational methods to examine the attack of methyl thiolate on each of the three electrophilic centers in a simple analogue of the 1,2-dithiolan-3-one 1-oxide heterocycle found in leinamycin. Calculations were performed at the MP2/6-311+G(3df,p)//B3LYP/6-31G level of theory with inclusion of solvent effects. The results indicate that the most reasonable mechanism for thiol-mediated activation of leinamycin involves initial attack of thiolate at the S2'-position of the antibiotic's 1,2-dithiolan-3-one 1-oxide heterocycle, followed by conversion to the 1,2-oxathiolan-5-one intermediate (3).

Antibiotics, Antineoplastic↗
PubMed2003

1,2-dithiolan-3-ones and derivatives structurally related to leinamycin. Synthesis and biological evaluation.

Leinamycin, an antitumor antibiotic isolated from Streptomyces sp., shows a 1,2-dithiolan-3-one 1-oxide heterocycle that appears to be involved in the biological activity. Several derivatives related to 1,2-dithiolan-3-one 1-oxide have been prepared and their activity as antineoplastic agents have been investigated. The synthesized compounds did not display a significative antitumor or cytotoxic activity in vitro.

Antineoplastic Agents↗
PubMed2005

6-hydroxyquinoline-N-oxides: a new class of "super" photoacids.

N-Oxidation of hydroxyquinolines leads to a dramatic increase in their excited-state acidity. Time-resolved and steady-state emission characterization of 6-hydroxyquinoline-N-oxide and 2-methyl-6-hydroxyquinoline-N-oxide reveals a rich but less complex proton-transfer behavior than that of its parent hydroxyquinoline. The electronic effect of the oxidized heterocyclic nitrogen atom makes the excited state both less basic and more acidic than the parent and adds hydroxyquinoline N-oxides to the class of high-acidity excited-state proton donors in photochemistry and photobiology. Adiabatic photoinduced proton transfer is accompanied by the efficient nonreversible deoxygenation and 1-2 oxygen migration.

Journal Article↗
PubMed2006

2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potentiates nitrosation of a heterocyclic amine carcinogen by nitric oxide.

Although nitrosation plays an important role in initiation of carcinogenesis, the reactive nitrogen oxygen species (RNOS) mediating this reaction by multiple pathways have not been determined. The heterocyclic amine carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) was used as a target to investigate RNOS and pathways for potentiation of nitric oxide (NO)-mediated nitrosation. 2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (CPTIO) oxidizes NO to NO(2)(.) and was used as a tool to investigate NO(2)(.) potentiation of nitrosation. The IQ nitrosation product, 2-nitrosoamino-3-methylimidazo[4,5-f]quinoline ((14)C-N-NO-IQ), was monitored by HPLC. Autoxidation of NO, generated by spermine NONOate (2.4 microM NO/min) for 7.5 min, did not convert 10 microM (14)C-IQ to N-NO-IQ. However, the presence of 15 muM CPTIO resulted in 3 microM N-NO-IQ formation. Potentiation by CPTIO occurred at low and high fluxes of NO, 0.075 to 1.2 microM/min, and over a range of IQ to CPTIO ratios of 0.5 to 10. A significant portion of N-NO-IQ formation was insensitive to azide (10 mM) inhibition, suggesting oxidative nitrosylation. NADH (0.02 mM) did not alter nitrosation by autoxidation, but effectively inhibited potentiation by CPTIO. Ascorbic acid (0.2 mM) and 5,5-dimethyl-1-pyrroline N-oxide (30 mM) inhibited nitrosation with or without CPTIO, while superoxide dismutase was not inhibitory. The RNOS produced by CPTIO had a 27-fold greater affinity for IQ than those produced by autoxidation. Results are consistent with NO(2)(.) or a RNOS like NO(2)(.) potentiating IQ oxidative nitrosylation. Nitrosation occurring at both low and high fluxes of NO can contribute to carcinogenesis.

Benzoates↗
PubMed2001

Antioxidative activity of volatile chemicals extracted from beer.

Volatile chemicals obtained from a commercial beer by liquid-liquid continuous extraction were evaluated for antioxidant activity. The inhibitory ability of this extract toward the conversion of hexanal to hexanoic acid was monitored over a 35-day period. The volatile extract demonstrated >99% effectiveness at inhibiting hexanal oxidation at 50 microg/mL, comparable to that of the natural antioxidant alpha-tocopherol (vitamin E). Volatile compounds contained in the extract were isolated and identified by gas chromatography-mass spectrometry (GC-MS). From the volatile constituents identified in beer extract, phenylethyl alcohol, maltol, and 2-furanmethanol were examined for antioxidative activities. At a concentration of 500 microg/mL, maltol and 2-furanmethanol demonstrated approximately 95 and 100% inhibition of hexanal oxidation over 35 days, respectively. Phenylethyl alcohol did not show any appreciable level of inhibition of hexanal oxidation. Heterocyclic compounds, some of which are known to possess antioxidative activities, were also identified in the volatile extract.

Aldehydes↗