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At least 703 records · Page 39Linked to original sources
PubMed2004

The antennal benzoic acid receptor cell of the female silk moth Bombyx mori L.: structure-activity relationship studies with halogen substitutes.

Studies on structure-activity relationships were carried out to characterize the response specificity of the benzoic acid cell of the female of the moth Bombyx mori by means of single sensillum electrophysiological recordings. We demonstrated that this cell type responds best to a natural key substance (benzoic acid) and has similar response profiles for less effective compounds, including various halogen substitutes of benzoic acid, benzaldehyde and other derivates of the key compound. Using different halogen substitutes (F, Cl, Br, I), we showed that the cellular response decreases with increasing atomic size of the substitute and that halogen substitutes were most effective in the meta-position. Thus, m-fluor benzoic acid was even more effective than benzoic acid. These results indicate that a critical feature of the stimulus molecule is the inductive effect generated by the halogen substitutes. Increasing the atomic size of the halogen substitute impairs the recognition of the molecule by the receptor cell, possibly due to steric effects. Decreasing the electron density in the aromatic ring improves the receptor response. The benzoic acid receptor cell can be considered as specialist despite not being involved in pheromone detection as it responds maximally to a key substance and has similar response profiles for less effective compounds.

Action Potentials↗
PubMed2004

1-(4-Bromophenyl)-2-methyl-4-nitro-1H-imidazole: bifurcated Br...O halogen-nitro bonds.

The crystal packing of the title compound, C(10)H(8)BrN(3)O(2), is determined mainly by relatively strong bifurcated C-Br...O halogen-nitro bonds. Both O atoms are involved in this interaction in an almost symmetrical manner and the difference [0.078 (3) A] between the Br...O contact lengths is one of the smallest found in similar compounds. Halogen bonds and weak hydrogen bonds connect molecules into layers which are stacked along the [100] direction.

Journal Article↗
PubMedDate not supplied

[Biotransformation in occupational medicine: the role of hepatic cytochrome P-450 in the mechanism of action and the biological monitoring of occupational toxic compounds].

Biotransformation is an important step in the investigation of occupational toxic chemicals. This is because the knowledge of the metabolic pathways and the enzymes involved in the activation and/or detoxication of xenobiotics may help in understanding the mechanism of toxicity and to rationalize the biological monitoring of exposed subjects. The largest enzymatic system involved in the biotransformation of industrial chemicals is cytochrome P-450, a family of haemoproteins capable of metabolizing a vast number of lipophilic, structurally different compounds. The study of the various metabolic reactions of this peculiar group of enzymes has greatly contributed to a) the clarification of the mode of action of several classes of occupational toxic and/or carcinogenic compounds, such as aromatic amines, polycyclic aromatic hydrocarbons, halogenated alkanes, benzene compounds and others, and b) the improvement of risk assessment in the biological monitoring of the exposed subjects, by allowing the toxicological significance (activation/detoxication) of single metabolites to be better understood.

Animals↗
PubMed1982

Dominant lethal studies in rats with 1,2-dibromo-3-chloropropane and its structurally related compounds.

Dominant lethal studies were conducted in SD male rats with 5 halogenated 3-carbon compounds that are structurally similar to a known mutagen 1,2-dibromo-3-chloropropane (DBCP). 1,2,3-Tribromopropane induced dominant lethal mutation especially in the early spermatid stage. This finding was almost the same as that obtained after DBCP treatment. The estimated dominant lethal mutation index of a group treated with 1,2-dibromopropane was marginal at week 1 of testing. On the other hand, bromopropane, 1,2,3-trichloropropane and 1-chloropropane produced negative responses for induction of dominant lethals.

Animals↗
PubMedDate not supplied

Chlorophyll a fluorescence: a tool for the investigation of toxic effects in the photosynthetic apparatus.

The effects of environmental pollutants, such as triazines, urea herbicides, phenols, nitro aromatic compounds, aldehydes, hydrogen sulfide, volatile halogenated aliphatic and aromatic compounds, and alkylbenzenes, the photosynthesis of green algae were investigated by using detailed analysis of chlorophyll a fluorescence. Application of quenching analysis by means of a pulse amplitude-modulated fluorometer allows the discrimination of different modes of action. Blocks of the electron-transport chain, the action of uncouplers, and fluorescence quenching by nitroaormatic compounds could be distinguished. Hydrogen sulfide and short-chain aldehydes seem to react in the same way, probably by reaction with components of the electron-transport chain. Nonreactive volatile compounds affect chlorophyll fluorescence in a strictly hydrophobicity-dependent manner. The quenching analysis suggests an inhibition of utilization of proton-motive force for ATP synthesis. Detailed analysis of fluorescence patterns may be of great help for identification of toxic pollutants and their sources.

Adenosine Triphosphate↗
PubMed2004

Derivatisation of 4-nonylphenol and bisphenol A with halogenated anhydrides.

The aim of this work is to synthesize and characterise the halogenated derivatives of the endocrine disrupting compounds (EDCs) 4-nonylphenol (4-NP) and bisphenol A (BPA). Characterisation was performed after gas chromatographic (GC) separation on-line coupled to mass spectrometric (MS) detector and a Fourier Transform Infrared (FTIR) spectroscopic detector. Further structure elucidation was done applying Nuclear Magnetic Resonance spectroscopy (NMR). Two different approaches for the preparation of derivatives were evaluated. At first trifluoroacetyl derivatives were synthesized by the reaction of trifluoroacetic acid (TFA) anhydride and the EDCs in acetonitrile at a temperature of 50 degrees C for 30 minutes. In a second step the 4-NP was derivatised using trichloroacetic acid anhydride and triethylamine in diethyl ether at 20 degrees C for 30 minutes. After synthesis the halogenated NP and BPA derivatives were characterised applying GC/MS, GC/FTIR and NMR. Three indices for a successful derivatisation were observed: El-GC/MS proved a complete derivatisation presenting a characteristic fragmentation pattern for each derivative. The IR spectra obtained by GC/FTIR after derivatisation and separation confirmed the loss of the phenolic O-H stretching vibration at 3,600 cm(-1) while typical absorptions for halogenated compounds now were observed. The NMR-spectra contained the predicted resonance signals.

Acetic Anhydrides↗
PubMed1991

Duocarmycins, new antitumor antibiotics produced by Streptomyces; producing organisms and improved production.

Six duocarmycins have been discovered during our search for new antitumor antibiotics and they showed extremely potent cytotoxic activity with IC50 values of 10(-12) M-10(-9) M on HeLa S3 cell. Three different producing strains isolated from soils were taxonomically assigned as Streptomyces. Duocarmycin A was unstable in culture broth, so improved culture conditions were designed to produce a high titer of duocarmycins B1, B2, C1 and C2 which are halogenated seco-compounds of duocarmycin A. Duocarmycin SA, one of the most potent cytotoxic agents yet discovered, was shown to be more stable in culture media than duocarmycin A, despite the structural similarity on their spirocyclopropylhexadienone moiety. In contrast to the duocarmycin A fermentation, no halogenated seco-compounds of duocarmycin SA were detected in culture broth supplemented with Br- or Cl-. All duocarmycins could be produced using one producing strain with improved media and culture conditions.

Antibiotics, Antineoplastic↗
PubMed1998

Iodinated and fluorinated steroid 2'-aryl-[3,2-c] pyrazoles as potential glucocorticoid receptor imaging agents.

We have synthesized several halogenated steroids as potential glucocorticoid receptor mediated imaging agents. These compounds are analogs of aryl-pyrazolo steroids, similar to the potent glucocorticoid, cortivazol. Compounds containing the halogens, iodine, bromine, and fluorine, as well as the E- and Z-iodovinyl side chain at the para position of 2'-phenyl-11 beta,17,21-trihydroxy-16 alpha-methyl-20-oxo-pregn-4-eno[3,2-c] pyrazole were prepared. They were tested as ligands for the glucocorticoid receptor by competition for the binding of [3H]dexamethasone and for glucocorticoid potency by the induction of alkaline phosphatase in HeLa cells. None of the iodinated steroids were good ligands for the glucocorticoid receptor or potent glucocorticoids. The bromo analog was only slightly better than the iodinated steroids as a ligand, and it had a potency in the HeLa cell assay about half that of dexamethasone. The fluoro analog good binding to the glucocorticoid receptor and was a very potent glucocorticoid, approximately seven times that of dexamethasone. Consequently, it appears that the fluoro steroid, 2'-(4-fluorophenyl)-11 beta,17,21-trihydroxy-16 alpha-methyl-20-oxo-pregn-4-eno[3,2-c] pyrazole, when labeled with 18F, would make an excellent glucocorticoid receptor-mediated imaging agent for positron emission tomography.

Animals↗
PubMed1983

A steady state kinetic analysis of the reaction of chloroperoxidase with peracetic acid, chloride, and 2-chlorodimedone.

The chloroperoxidase-peracetic acid-chloride-2-chlorodimedone system is used as a model for the investigation of enzymatic halogenation reactions. Systematic variation of the concentrations of the three substrates under steady state conditions yields sets of kinetic parameters containing both kinetic and mechanistic information. Three distinct enzyme species are involved in the halogenation cycle: native enzyme, compound I, and a short-lived halogenating intermediate. Analysis of the kinetic data is complicated by the fact that chloride serves as a substrate in the second step and as an inhibitor of the first step of the overall halogenation reaction. The inhibitor binding site on the native enzyme must be protonated prior to the binding of chloride. Chloride appears to be a competitive inhibitor for both compound I formation and cyanide binding to chloroperoxidase. Only the latter reaction can be studied directly in stopped-flow experiments since compound I disappears rapidly by reacting with chloride present in solution. Rate constants are calculated for the individual steps of the reaction at four different pH values. The rate constant for compound I formation is independent of pH, but the actual rate is reduced at lower pH values due to pH dependence of the chloride inhibition. The rate constant for the oxidation of chloride by compound I decreases with increasing pH. The rate of the halogenation step appears to be independent of pH.

Acetates↗
PubMed2002

Halogenated diazirines as photolabel mimics of the inhaled haloalkane anesthetics.

The inhaled anesthetics are low affinity volatile compounds whose mechanism of action remains unclear, in part due to the difficulty of determining their binding targets. Photolabeling may help resolve this difficulty, and thus we have synthesized six compounds (four previously unreported) with structural and physical similarity to halothane (1-bromo-1-chloro-2,2,2-trifluoroethane), a commonly used clinical anesthetic. These compounds incorporate either a diazo, diazirine, or azido group to provide photolability in the long-UV range and to provide a highly reactive photolysis product. While several of the compounds have immobilizing activity in tadpoles, it is complicated by either toxicity or very low potency. One compound however, a halogenated three-carbon diazirine 4, is a potent anesthetic, is apparently nontoxic, potentiates GABA(A) Cl(-) currents, and stabilizes serum albumin, all of which are features of halothane. When tagged with radioactivity, this compound should serve as a reasonable probe of haloalkane anesthetic binding targets and sites.

Anesthetics, Inhalation↗
PubMed2003

Halophenyl furanopyrimidines as potent and selective anti-VZV agents.

Bicyclic furano pyrimidines have been previously reported by us to be highly potent and selective inhibitors of varicella zoster virus (VZV). p-Alkyl phenyl analogues are particularly potent with EC50 values below 1 nM. In this article we report the synthesis and anti-VZV activity of a series of halophenyl analogues, with variation in the nature (F, Cl, Br) and location (o, m, p) of the halogen substituent. The compounds show a range of activities from ca. 10 nM to > 50 microM. In most cases, ortho substitution leads to greatest activity, meta substitution is in general poor, and the effect of p-substitution shows a marked dependence on the halogen atom. The p-fluorophenyl compound is unique amongst compounds of this class in being inactive as an antiviral. The possible origins of these marked SARs are discussed.

Antiviral Agents↗
PubMed1981

Selective enrichment of Pseudomonas spp. defective in catabolism after exposure to halogenated substrates.

Significant selective enrichments of mutants defective in catabolic pathways can be achieved by exposure of pseudomonad cells to halogenated analogs of growth substrates. Between 3 and 95% of viable clones rescued from such enrichments have been defective in specific catabolic pathways. This has been demonstrated for eight different catabolic pathways for aromatic compounds in pseudomonads, in which the genes are located on plasmids or on the chromosome. The plasmid-encoded pathways studied include those for the catabolism of p-cymene (CYM), m- and p-xylenes (TOL), naphthalene (NAH), salicylate (SAL), and 4-methylphthalate (MOP), and the chromosome-encoded pathways include those for p-hydroxybenzoate, monohydric phenols, and p-anisate utilization. The recalcitrance of halogenated compounds may, in part, be explained by these observations, which introduce an as yet not widely recognized factor in assessment of biodegradability of halogenated compounds and their effects on the transformation of the natural substrates.

Benzene Derivatives↗
PubMed2004

An extremely active catalyst for the Negishi cross-coupling reaction.

A new catalyst system for the Pd-catalyzed cross-coupling of organozinc reagents with aryl halides (Negishi coupling) has been developed. This system permits efficient preparation of hindered biaryls (tri- and tetra-ortho-substituted), functions effectively at low levels of catalyst, and tolerates a wide range of functional groups and heterocyclic substrates. A systematic study of ligand structure was performed and was correlated with catalyst activity.

Biphenyl Compounds↗
PubMed2005

Alkyne haloallylation [with Pd(II)] as a core strategy for macrocycle synthesis: a total synthesis of (-)-haterumalide NA/(-)-oocydin A.

The rarely used haloallylation reaction, first described by Kaneda and Teranishi in 1974, employs a Pd(II) catalyst to join an alkyne with an allylic halide to produce a 1-halo-1,4-diene subunit. It is shown here that functionalized and tertiary allylic chlorides perform well as substrates in this reaction under the action of PdCl2(PhCN)2 in THF solution. When the alkyne is added slowly to the reaction mixture, the two reactants can be used in a nearly equimolar ratio. This fact means (i) that reasonably complex pairs of alkyne and allylic halide substrates are tolerated and, therefore, (ii) that an intramolecular version of the reaction is suitable as a core strategy for complex molecule construction. The latter is demonstrated in the macrocyclization of 2b to 17b, which is the central step in the total synthesis of (-)-haterumalide NA/(-)-oocydin A (1) that is reported. The final key to the completion of the synthesis was the choice of the acid-labile PMB ester of 1 as the penultimate intermediate.

Alkynes↗
PubMed1996

Mapping the melatonin receptor. 4. Comparison of the binding affinities of a series of substituted phenylalkyl amides.

A series of 2-, 3-, and 4-substituted phenylalkyl amides were prepared as potential melatonin analogs in order to investigate the nature of the binding site of the melatonin receptor in chicken brain. The length of the alkyl chain was systematically varied from n = 1 to 4, and methoxyl substituents were incorporated into the phenyl ring at the 2-, 3-, and 4-positions. The maximum binding affinity was found to occur when n = 3 and when the methoxyl substituent was in the 3-position, the direct analog of the carbon framework of melatonin in which the 1,2-atoms of the indole ring have been removed. Whereas there was only a relatively small decrease in binding affinity for the corresponding 2-methoxy derivatives, 4-methoxyl substitution led to a large decrease in binding affinity, suggesting that the binding sites for the side chain and methoxyl group could not now be occupied at the same time. As in the indole analogs of melatonin, replacement of the methyl group of the amide by a longer alkyl chain led to an increase in binding affinity for ethyl and propyl with a subsequent decrease in binding affinity for butyl chains. Thus N-propanoyl-3-(3-methoxyphenyl)propanamine (6f) has a binding affinity of 5.6 nM, a remarkably high affinity for so simple a compound. Substitution of halogen for 3-methoxyl in the propanamide series gave a series of compounds with lower, but still substantial, binding affinities, the 3-chloro derivative 7e showing the highest affinity, 113 nM. In the case of the 3-fluoro propanamides, a maximum in the binding affinity was not observed in the series synthesized, and these derivatives will merit further exploration. These results demonstrate the utility of simple, readily modified phenylalkylamines as a "framework" for studying the effect of changes in the nature and position of substituents on the melatonin receptor binding affinity.

Amides↗
PubMed2002

Mild alpha-halogenation reactions of 1,3-dicarbonyl compounds catalyzed by Lewis acids.

Lewis acid Mg(ClO4)2, combined with NBS, in CH3CN or EtOAc provided mild and fast bromination of 1,3-dicarbonyl compounds. In particular, this protocol could be applied to the alpha-monobromination of alpha-unsubstituted beta-keto esters. Similar Lewis acid catalysis was also extended to the alpha-chlorination and iodination of 1,3-dicarbonyl compounds with NCS and NIS, respectively.

Journal Article↗