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PubMed2002

Synthesis of unsymmetrical aroyl acyl imides by aminocarbonylation of aryl bromides.

Aroyl imides were prepared by a palladium-catalyzed aminocarbonylation reaction of aryl bromides with carbon monoxide and primary amides in good yields (58-72%). The reactions were carried out under mild conditions (5 bar, 120 degrees C) using 1 mol % of a palladium phosphine complex. Several aryl bromides were reacted with formamide, acetamide, benzamide, and benzenesulfonamide, respectively. For activated aryl bromides, a phosphine-to-palladium ratio of 2:1 was sufficient, but less reactive aryl bromides required a ligand-to-palladium ratio of 6:1 in order to stabilize the catalyst and achieve full conversion. The imides were very sensitive to aqueous basic conditions and were easily converted to aroyl amides or benzoic acids.

Journal Article↗
PubMed2002

2-Trimethylsilylethyl sulfides in the von Braun cyanogen bromide reaction: selective preparation of thiocyanates and application to nucleoside chemistry.

Mixed 2-(trimethylsilyl)ethyl sulfides were synthesized and used in the von Braun cyanogen bromide reaction for preparing selectively thiocyanates in high yield. We show here that this cleavage reaction is highly selective in methanol in comparison with the reaction of the corresponding non-silyl sulfide analogues. This reaction was applied to the synthesis of nucleosidic thiocyanates such as the new nucleosides 14 and 18 in the search for mechanism-based inhibitors of ribonucleoside diphosphate reductase and bioactive molecules. The selective cleavage is possible for sulfides bearing hydroxyl functions and aromatic rings. The reactions of cyanogen bromide as cyanating and brominating agent were observed for the first time under the same conditions with the naphthoxyhexyl 2-trimethylsilylethyl sulfide 7, which, treated with cyanogen bromide in dichloromethane, led selectively to the p-bromonaphthoxyhexyl thiocyanate 10 in 89% yield. Another reaction induced by cyanogen bromide was observed in dichloromethane with the 2-(trimethylsilylethyl)thio nucleoside 13, which gives the corresponding symmetrical disulfide 21 in good yield.

Bromine↗
PubMed2004

Simple amine/Pd(OAc)(2)-catalyzed suzuki coupling reactions of aryl bromides under mild aerobic conditions.

A new palladium catalyst (DAPCy) made from Pd(OAc)(2) and commercially available, inexpensive dicyclohexylamine has been developed for the Suzuki coupling reaction of aryl bromides with boronic acids to give the coupling products in good to high yields. The air-stable catalyst was characterized and well-defined by X-ray crystallography. A catalytic system involving DAPCy in dioxane demonstrates a temperature-dependent reactivity toward aryl bromides with different electronic substituents, and selectively couples electron-deficient aryl bromides with boronic acids over electron-rich ones at room temperature. Another catalytic system employing DAPCy in EtOH provides a general and convenient method to prepare biaryls from aryl bromides and boronic acids with a broad range of functional groups at room temperature and under aerobic conditions.

Amines↗
PubMed2004

Aqueous-phase, palladium-catalyzed cross-coupling of aryl bromides under mild conditions, using water-soluble, sterically demanding alkylphosphines.

Sterically demanding, water-soluble alkylphosphines have been used in combination with various palladium salts in Suzuki, Sonogashira, and Heck couplings of aryl bromides under mild conditions in aqueous solvents. The tert-butyl-substituted ligands 2-(di-tert-butylphosphino)ethyltrimethylammonium chloride (t-Bu-Amphos) and 4-(di-tert-butylphosphino)-N,N-dimethylpiperidinium chloride (t-Bu-Pip-phos) in combination with palladium(II) salts were found to give catalysts that were significantly more active than catalysts derived from tri(3-sulfonatophenyl)phosphine trisodium (TPPTS). Suzuki couplings of unactivated aryl bromides occurred efficiently at room temperature in water/acetonitrile and water/toluene biphasic mixtures or in neat water. Notably, Suzuki couplings of hydrophilic aryl bromides gave high yields without using organic solvents for the reaction or purification. This methodology has been applied to a highly efficient synthesis of diflunisal. The catalyst derived from t-Bu-Amphos was recycled three times in Suzuki couplings in water/toluene before catalyst activity began to significantly drop. The average yield of four cycles was >80% per cycle. Heck and Sonogashira couplings were carried out under mild conditions (50 and 80 degrees C, respectively) with unactivated aryl bromides to give coupled products in high yield.

Journal Article↗
PubMed2005

Room-temperature Negishi cross-coupling of unactivated alkyl bromides with alkyl organozinc reagents utilizing a Pd/N-heterocyclic carbene catalyst.

A high-yielding cross-coupling reaction of unactivated alkyl bromides possessing beta-hydrogens with alkylzinc halides utilizing a Pd/N-heterocyclic carbene (NHC) catalyst at room temperature is described. A variety of Pd sources, Pd2(dba)3, Pd(OAc)2, or PdBr2, with the commercially available ligand precursor 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride (IPr.HCl) successfully coupled 1-bromo-3-phenylpropane with n-butylzinc bromide in THF/NMP. An investigation of different NHC precursors showed that the bulky 2,6-diisopropylphenyl moiety was necessary to achieve high coupling yields (75-85%). The corresponding ethyl analogue was moderately active (11%). A range of unsymmetrical NHC precursors were prepared and evaluated. The ligand precursor containing one 2,6-diisopropylphenyl and one 2,6-diethylphenyl afforded the coupling product in 47% yield, clearly suggesting a direct relationship between the steric topography created by the flanking N-substituents and catalyst activity. Under optimal conditions, a number of alkyl bromides and alkylzinc halides possessing common functional groups (amide, nitrile, ester, acetal, and alkyne) were effectively coupled (61-92%). It is noteworthy that beta-substituted alkyl bromides and alkylzinc halides successfully underwent cross-coupling. Also, under these conditions alkyl chlorides were unaffected.

Journal Article↗
PubMed2004

Thermodynamics of micellization and adsorption of three alkyltrimethylammonium bromides using isothermal titration calorimetry.

Studies of the thermodynamic properties of micellization, as well as the enthalpy change of adsorption (displacement), were conducted using isothermal titration calorimetry (ITC). The cationic surfactants, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, and hexadecyltrimethylammonium bromide or cetyltrimethylammonium bromide were used. Adsorption studies were performed utilizing HiSil 233 precipitated silica as the substrate. The thermodynamics of micellization were studied at 28, 30, and 35 degrees C using ITC. DeltaHdil was calculated and graphed versus concentration in order to determine DeltaHmic and critical micelle concentration. From these data, DeltaGmic and DeltaSmic were also determined and found to be in agreement with values previously determined using traditional temperature-variation methods. The thermodynamics of adsorption were also determined at the above temperatures using ITC. Using the results, the heat of displacement, Qdisp, and enthalpy of displacement, DeltaHdisp, were calculated. A plot of DeltaHdisp as a function of concentration was generated and used to interpret the mechanism of adsorption in the four regions of a typical cationic surfactant adsorption isotherm.

Journal Article↗
PubMed1998

Effect of ionic state of 2'-deoxyguanosine and solvent on its aralkylation by benzyl bromide.

To extend studies of the aralkylation of nucleic acid components under a variety of solvent conditions, we determined product distributions from the reactions of benzyl bromide with 2'-deoxyguanosine and the anion of 2'-deoxyguanosine in 2,2, 2-trifluoroethanol (TFE) and compared these distributions with those from the reaction of the anion with benzyl bromide in N, N-dimethylacetamide (DMA). 7-Benzylguanine was the only benzylated product detected in the reaction with the neutral nucleoside in TFE. In striking contrast, the reaction of the anion of 2'-deoxyguanosine with benzyl bromide in TFE produced N2-benzyl-2'-deoxyguanosine in significant yield and with high selectivity. The reaction of the anion of 2'-deoxyguanosine with benzyl bromide in DMA produced products derived only from reaction at the 1- and/or 7-position of the nucleoside. The weakly nucleophilic but protic polar solvent TFE and the iminolate tautomeric form of the 2'-deoxyguanosine anion appear to be essential for benzylation at the exocyclic N2-position.

Benzyl Compounds↗
PubMed2001

Optimisation and validation of a capillary electrophoresis method for the simultaneous determination of diazepam and otilonium bromide.

A simultaneous assay of diazepam and otilonium bromide in coated tablets by capillary zone electrophoresis (CZE) was developed. The influence of various parameters (voltage, temperature, buffer concentration and pH, ethanol percentage) on analysis time and on the theoretical plates of the two peaks was investigated by means of experimental design. A response surface study was carried out by means of a 27-run D-optimal matrix. The best background electrolyte was found to be 0.13 M, pH 2.9 Britton-Robinson buffer, containing 10% v/v ethanol. Other optimised parameters were voltage (30 kV) and temperature (30 degrees C). The UV detector for quantitation of otilonium bromide and diazepam was set at 280 nm and 230 nm, respectively. Procaine hydrochloride was used as internal standard and run time was less than five minutes. Validation was performed, for drug substance and drug product, according to ICH3 guidelines. For drug product the recovery for otilonium bromide and diazepam ranged from 98.3% to 101.2% and from 97.1% to 99.0%, respectively; the RSD values found for otilonium bromide and diazepam ranged from 2.4% to 3.0% and from 1.1% to 4.5%, respectively.

Calcium Channel Blockers↗
PubMed2004

Novel one-dimensional structures and solution behaviour of copper(II) bromide and chloride complexes of a new pentapyridyldiamine ligand.

Copper(II) bromide and chloride complexes of the new heptadentate ligand 2,6-bis(bis(2-pyridylmethyl)amino)methylpyridine (L) have been prepared. For the bromide complexes, chains of novel, approximately C2-symmetric, chiral [Cu2(L)Br2]2+ 'wedge-shaped' tectons are found. The links between the dicopper tectons and the overall chirality and packing of the chains are dictated by the bromide ion content, not the counter anion. In contrast, the chloride complexes exhibit linked asymmetric [Cu2(L)Cl3]+ tectons with distinct N3CuCl2 and N4CuCl2 centres in the solid. The overall structures of the dicopper bromide and chloride units persist in solution irrespective of the halide. The redox chemistry of the various species is also described.

Journal Article↗
PubMed1972

The location of spermine in bacterial ribosomes as indicated by 1,5-difluoro-2,4-dinitrobenzene and by ethidium bromide.

1. When the binding of ethidium bromide to rRNA is measured both in the presence and in the absence of spermine, by spectrophotometric titrations, by gel filtration, or by the changes in fluorescence intensity, spermine competes with ethidium bromide for sites on the rRNA; under the conditions used in these experiments ethidium bromide is bound to the double-stranded regions of rRNA. 2. When an excess of ethidium bromide is added to ribosomes from Bacillus stearothermophilus approx. 80% of the endogenous spermine is displaced from the ribosomes. 3. [(14)C]Spermine is fixed to ribosomes by either formaldehyde or 1,5-difluoro-2,4-dinitrobenzene. Most of the [(14)C]spermine, fixed to ribosomes by 1,5-difluoro-2,4-dinitrobenzene, attaches to the ribosomal protein. 4. It is concluded that most of the endogenous spermine is bound to the double-stranded RNA in ribosomes, and that some of these double-stranded regions to which spermine is attached also have ribosomal proteins bound to them.

Bacillus↗
PubMed2000

Improved delivery of ipratropium bromide using Respimat (a new soft mist inhaler) compared with a conventional metered dose inhaler: cumulative dose response study in patients with COPD.

Respimat (RMT) is a reusable, propellant-free, soft mist inhaler (SMI), a novel device for inhalation therapy. We conducted a three-period cross-over study to evaluate the safety and efficacy of cumulative doses of ipratropium bromide inhaled from RMT (Two dose levels) or from a pressurized metered dose inhaler (MDI), in 36 patients with chronic obstructive pulmonary disease (COPD). The bronchodilator effect of ipratropium bromide was greater when administered via RMT (10 or 20 microg per puff, given double-blind within device, to total doses of 160 or 320 microg) than via MDI (20 microg per puff, total dose 320 microg). The bronchodilator effects of the 160 and 320 microg doses delivered via RMT were similar. Cumulative ipratropium bromide doses of 320 microg given via MDI or RMT and 160 microg given via RMT produced similar safety profiles. Between 45 min after the first drug inhalation and 45 min after the final dose, greater bronchodilatory effect was obtained from half the cumulative dose of ipratropium (RMT 10 microg per puff) when compared with the MDI (20 microg per puff). Therefore, ipratropium bromide delivered by RMT is as safe as, and can be more effective than, the MDI on acute administration in patients with COPD.

Administration, Inhalation↗
PubMed2002

Bronchodilating effect of oxitropium bromide in heart disease patients with exacerbations of COPD: double-blind, randomized, controlled study.

Anti-cholinergic agents are considered the bronchodilator therapy of first-choice in the treatment of patients with stable chronic obstructive pulmonary disease (COPD) associated with heart disease since they may be as effective or more effective than inhaled beta2-agonists and, moreover, they do not interact with cardiac beta-adrenoceptors. The aim of our study was to evaluate the bronchodilator activity of oxitropium bromide in outpatients suffering from exacerbations of COPD associated with heart diseases (ischaemic heart disease and/or arrhythmias). We recruited 50 consecutive outpatients (33 males and 17 females, mean age 68.6 years, 15 current smokers and 35 ex-smokers). Each patient performed body plethismography in basal condition and 30 min after inhalation of 200 microg metered dose inhaler (MDI) oxitropium bromide administered by a device (Fluspacer). FEV1, FVC, MMEF25-75, sRaw and tRaw were evaluated. Thirty minutes after 200 microg oxitropium bromide administration, we observed a significant improvement in FEV1 11.6% +/- 1 (mean +/- SEM) (P<0.01); FVC, MMEF25-75 sRaw variation was respectively: 9.2% +/- 0.6, 31.4 +/- 2.9, -19.9 +/- 1.1. Placebo did not significantly change pulmonary function. Our data suggest that oxitropium bromide bronchodilator activity is effective in exacerbations of COPD.

Acute Disease↗
PubMed1998

Personal and environmental air sampling of methyl bromide during experimental greenhouse fumigation.

In this investigation methyl bromide, a widely used soil fumigant, was investigated with respect to workers exposure and environmental fortification at the greenhouses of Thessaloniki area, Northern Greece. By means of personal and environmental air sampling through charcoal, methyl bromide concentration was measured by gas chromatography using a capillary OV-1 column at 45 degrees C and flame ionization detector (FID). Personal air sampling for two workers showed that the levels of exposure to methyl bromide were 89 and 92 mg/m3 respectively. These values exceeded the safety limits. The mean maximum and mean minimum concentrations in the environmental air samples inside the greenhouse, for 8 hours duration, were 142 mg/m3 and 4 mg/m3, respectively. These concentrations were determined within four and eleven days after the application of methyl bromide.

Adsorption↗
PubMed1984

Neurobehavioral assessment of chronic low-level methyl bromide exposure in the rabbit.

The research reported here was intended to identify the concentration at which methyl bromide begins to produce neurotoxic effects in the rabbit, a species known to be sensitive to this compound. Rabbits were exposed via inhalation to 27 ppm methyl bromide over a period of 8 mo for a total exposure duration of 900 h. Biweekly neurobehavioral tests, consisting of the latency rates of the ulnar and sciatic nerves and the amplitude of the eyeblink reflex of the orbicularis oculi muscle, failed to uncover any untoward consequences of the exposures. The rabbits gained weight and otherwise appeared to be healthy. In contrast to reports available in the literature, these findings suggest that long-term exposures to methyl bromide, in the present concentration range, are tolerated by this species. Also detailed in this report is the course of recovery of a separate group of rabbits previously given subchronic exposures to 65 ppm methyl bromide. These animals developed severe neuromuscular losses and had impaired blink reflexes and body weights. The symptoms partially subsided within 6-8 wk after removal from the exposures, suggesting that recovery from a nonfatal but seriously debilitating exposure is possible.

Animals↗
PubMed1996

Structural characterization by mass spectrometry of hemoglobin adducts formed after in vivo exposure to methyl bromide.

A mass spectrometric procedure is described for the structural study of the adducts formed in human hemoglobin by in vitro exposure of erythrocytes to the alkylating agent methyl bromide using different protein to reagent ratios. Peptide mapping by HPLC and tandem mass spectrometry allowed location of methylated amino acids within the protein sequence. A prominent reactivity of several nucleophilic side chains in human hemoglobin subunits was observed, which was modulated by the concentration of the alkylating agent. Cysteine residues, the main reactive sites, were fully methylated in hemoglobin exposed to a 10-fold excess of methyl bromide, differently from other residues, including histidines, showing a heterogeneous pattern of methylation that was largely directed by their environment. No evidence of methylation was found at the heme proximal histidines beta92 and alpha87. A more selective methylation was obtained when the ratio methyl bromide: hemoglobin was lowered to about 1:1. In this last case only specific residues were reactive. Among them, the N-terminal amino group of both alpha- and beta-globins, cysteine 104 in the alpha-chain and cysteine 93 (not cysteine 112) in the beta-chain, indicating a different accessibility to reaction of the sulfhydryl groups on the protein chain. Thus hemoglobin side chains are selectively modified and the degree of modification at each site is a function of the position of the single amino acid residue within the protein quaternary structure, raising the possibility that alterations of structure and functional properties of human hemoglobin following exposure to alkylating agents may be mediated through such covalent protein modifications. The results obtained demonstrate the usefulness of the analytical approach for the characterization of hemoglobin adducts with methyl bromide or similar compounds, which can constitute the basis for biomonitoring of human exposure.

Alkylation↗
PubMed1975

A clarification of the complex spectrum observed with the ultraviolet circular dichroism of ethidium bromide bound to DNA.

Ethidium bromide intercalation strongly effects the circular dichroism spectrum of DNA in the region of 230-300 mu, in a complex manner. In this report we present a study that quantitizes the relationships of the circular dichroism spectrum in the region of 230-300 mu and the ethidium bromide induced optical activity centered around 308 mu. We present evidence of two hidden cooperative bands that are probably the negative counterparts of the 308 mu band and 330 mu shoulder positive cooperative bands. The hidden band is quantitatively characterized. We confirm that the direct effect of ethidium bromide on the DNA spectrum is simply linearly proportional to the amount of intercalated dye. We also observe that the ethidium bromide enters freely when there is a molecule intercalated for every 3 sites, but that the intercalation is more difficult when the molecule intercalates at every second site.

Animals↗
PubMed1976

Circular dichroism studies of ethidium bromide binding to the isolated nucleolus.

Circular dichroism in the 300-360 nm region and fluorescence induced by intercaltating binding of ethidum bromide to both DNA and RNA components were studied in isolated HeLa nucleoli. Both DNA and RNA compoents contribute to the induced dichroic elliticity. Digestion of nucleoli by RNase or DNase shows that most of the induced ellipticity comes from the DNA component. In nucleoli with an RNA/DNA = 0.8/1.0 the RNA component gives only 20% of the total ellipticity when measured at an ethidium bromide/DNA = 0.25. Spectro-fluorometric titration shows that ethidium bromide intercalates mostly into DNA in nucleoli. Both circular dichroism and fluorescence studies indicate that both DNA and RNA components in isolated nucleoli are less accessible to intercalating binding by ethidium bromide when compared to purified nucleolar DNA, DNA in chromatin or purified ribosomal RNA. Circular dichroic measurements of intercalating binding of ethidium bromide to to nucleoli may be used to study changes in nucleoli under different physiological or pathological conditions.

Binding Sites↗
PubMed1984

Protection by ipratropium bromide and metaproterenol against methacholine and histamine bronchoconstriction.

To establish relative protection against methacholine and histamine, 40 micrograms of ipratropium bromide, an anticholinergic compound, 1.3 mg of metaproterenol or placebo aerosols were administered by metered-dose inhaler prior to inhalation challenge with methacholine or histamine in nine asthmatic subjects. Double-blind, randomized challenges were performed. Subjects required a mean methacholine dose of 1.72 +/- 0.73 and 2.46 +/- 0.72 (Ln inhalation units), and mean histamine dose of 2.16 +/- 0.65 and 2.68 +/- 0.49, to cause a drop of 20% and 35% respectively in the FEV1 following the placebo. In the methacholine challenges, both ipratropium bromide and metaproterenol had significant protection as compared to placebo (P less than 0.001). There was no statistical difference in the degree of protection against methacholine between ipratropium bromide and metaproterenol. In histamine challenges, metaproterenol had significant protection as compared to the placebo, while ipratropium bromide did not protect against histamine.

Adolescent↗