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PubMed2002

Phase-vanishing reactions that use fluorous media as a phase screen. Facile, controlled bromination of alkenes by dibromine and dealkylation of aromatic ethers by boron tribromide.

In fluorous triphasic reactions, such as bromination of alkenes by dibromine and dealkylation of aromatic ethers by boron tribromide, the middle fluorous phase acts as a liquid membrane permitting passive transport of the reagents at the bottom to the top layer involving the substrates, thereby regulating the reactions.

Alkenes↗
PubMed1990

Compound I formation is a partially rate-limiting process in chloroperoxidase-catalyzed bromination reactions.

The kinetics of chloroperoxidase-catalyzed bromination and chlorination reactions were studied at various halide and hydrogen peroxide concentrations. At very high concentrations, both chloride (KI = 370 mM) and bromide (KI = 150 mM) are competitive substrate inhibitors versus hydrogen peroxide. Results at subinhibitory halide concentrations for bromination reactions (kcat = 4 ms-1, kcat/KPeroxide = 1.6 microM-1 x s-1 and kcat/KBr = 4.0 microM-1 x s-1) and chlorination reactions (kcat = 1.5 ms-1, kcat/Kperoxide = 2.3 microM-1 x s-1, and kcat/KBr = 0.32 microM-1 x s-1) indicate that halide oxidation is rate-limiting in chlorination reactions. However, in bromination reactions, both compound I formation and bromide oxidation are partially rate-limiting. This is the first documented case where compound I formation participates in determining the overall rate of a peroxidase reaction.

Binding, Competitive↗
PubMed2002

Distribution of organobrominated and organochlorinated contaminants in Belgian human adipose tissue.

We have measured the levels of flame retardants, polybrominated diphenyl ethers (PBDEs), in 20 recent human adipose tissues from Belgium and compared them to other organohalogen compounds such as polychlorinated biphenyls (PCBs), hexachlorobenzene, 2,2-bis(4-chlorophenyl)-1,1,1-trichloroethane (p,p'-DDT), and its metabolite, 2,2-bis(4-chlorophenyl)-1,1-dichloroethylene (p,p'-DDE). After Soxhlet extraction and cleanup on acidified silica solid-phase extraction cartridges, analysis was achieved by capillary gas chromatography/electron impact mass spectrometry. The method allowed the determination of 5 PBDE and 35 PCB congeners. Concentrations of PBDEs (sum of congeners IUPAC Nos. 28, 47, 99, 100, and 153) ranged between 2.2 and 11.7 ng/g lipid weight and were on the lower end of reported PBDE concentrations in European countries. The median value for the sum of PCBs (35 congeners) was 841 ng/g lipid weight and ranged from 286 to 1802 ng/g lipid weight. The median value for the sum of DDTs (calculated from p,p'-DDE and p,p'-DDT) was 290 ng/g lipid weight and ranged from 47 to 2802 ng/g lipid weight. The sum of PCBs showed a good correlation with the sum of DDTs (r=0.77, P<0.05), while the correlation with the sum of PBDEs was weaker (r=0.56, P<0.05). No age dependency was found for PBDEs (r=0.09), while PCBs and DDTs showed higher correlation coefficients with age (r=0.59 and 0.40, respectively, P<0.05).

Adipose Tissue↗
PubMed1992

Effect of glucose and ribose on microbial degradation of the herbicide bromoxynil continuously added to soil.

Bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) was continuously added to chernozem (Haplic typic) soil inoculated with a suspension of Pseudomonas putida capable of cometabolic decomposition of the compound in a hetero-continuous-flow cultivation setup. In the steady state, when glucose or ribose were simultaneously added, 90 and 47% of the added herbicide was degraded per day, respectively. If the saccharides were absent, only 10-27% of the herbicide was decomposed. Addition and removal of glucose feeding resulted in an increase and decrease, respectively, of the degradation intensity, irrespective of the amount of the bacterial decomposers present. Two degradation products, 3,5-dibromo-4-hydroxy-benzamide and 3,5-dibromo-4-hydroxybenzoic acid, were formed during cultivation. The total amount of bromine-containing compounds was reduced only in the presence of glucose.

Biodegradation, Environmental↗
PubMed2001

Determination and mass spectrometric investigation of a new mixed halogenated persistent component in fish and seal.

An unknown component that caused an intense signal in sample extracts of fish tissue was enriched and investigated using a variety of mass spectrometric techniques coupled to gas chromatographic separation. With the help of electron capture negative ion mass spectrometry (ECNI-MS) and electron impact mass spectrometry (EI-MS) it was established that the component carries 2Br and 3Cl atoms and forms a molecular ion at m/z 396. A concentrated solution of this mixed halogenated compound (MHC-1) was investigated by gas chromatography interfaced to electron impact high-resolution mass spectrometry (GC/EI-HRMS). Using full scan and SIM techniques, the molecular formula of MHC-1 was established to be C10H13Br2Cl3. This points toward MHC-1 having a monoterpene backbone. No chemical with this molecular formula has been synthesized, but two components with this composition have been earlier isolated from marine algae.

Alkenes↗
PubMed1998

D4T-5'-[p-bromophenyl methoxyalaninyl phosphate] as a potent and non-toxic anti-human immunodeficiency virus agent.

Three aryl phosphate derivatives of 2',3'-didehydro-2',3'-dideoxythymidine (d4T) were tested for their anti-human immunodeficiency virus (HIV) activity in peripheral blood mononuclear cells (PBMC) and thymidine kinase (TK)-deficient CEM T cells. Compared to the parent compound d4T, the lead compound d4T-5'-[p-bromophenyl methoxyalaninylphosphate] with a para-bromo substituent in the aryl moiety was 12.6-fold more potent in inhibiting p24 production (IC50 values: 44 nM versus 556 nM) and 41.3-fold more potent in inhibiting the reverse transcriptase (RT) activity (IC50 values: 57 nM versus 2355 nM) in HIV-infected TK-deficient CEM cells. None of the compounds exhibited any detectable cytotoxicity to PBMC or CEM cells at concentrations as high as 10,000 nM. To our knowledge, this is the first demonstration that the potency as well as selectivity index of the d4T aryl phosphate derivatives in TK-deficient cells can be substantially enhanced by introducing a single para-bromo substituent in the phenyl moiety.

Alanine↗
PubMed2004

State-of-the art of selective detection and identification of I-, Br-, Cl-, and F-containing compounds in gas chromatography and liquid chromatography.

This review article presents an overview of halogen-specific detection in gas chromatography (GC) and liquid chromatography (LC). Attention is primarily focused on the use of plasma emission spectroscopy and plasma mass spectrometry as detectors, but other halogen-selective detection principles are also mentioned. Different instrumental configurations are discussed both with respect to technical set-up and performance, the principal reasons for halogen-selective detection are highlighted, and recent applications are reviewed from areas such as environmental chemistry, petroleum characterization, and drug analysis.

Animals↗
PubMed1996

Lipopeptide conjugates: biomolecular building blocks for receptor activating membrane-mimetic structures.

A simple method for the derivatization of phospholipid subunits with short peptide sequences is presented. Amphiphilic conjugates of distearoylphosphatidylethanolamine (DSPE) and the minimal human thrombin-receptor peptide agonist SFLLRN were synthesized via coupling of the bromoacetyl derivative of DSPE (PEBr) with a thiol-terminated decapeptide of SFLLRN. Bromoderivatization of DSPE was performed by condensation of bromoacetic acid and DSPE, with an overall yield of 40%. Coupling of PEBr and the unprotected thiol-terminated decapeptide was performed in chloroform/methanol/water in the presence of triethylamine and afforded 25.5% of the lipopeptide. The compound was characterized by TLC, 1H-NMR (600 MHz) and mass spectrometry. Lipopeptide bioactivity was confirmed by a platelet aggregation assay. The EC50 of the all-L amino acid lipopeptide was 38 +/- 3 microM. The all-D conjugate was inactive. Model receptor-activating systems, including well-ordered assemblies of amphiphilic phospholipid-peptide conjugates, represent the first step in the construction of bioactive surfaces for tissue engineering based on a membrane-mimetic approach.

Bromine Compounds↗
PubMed2006

Novel anti-bacterials against MRSA: synthesis of focussed combinatorial libraries of tri-substituted 2(5H)-furanones.

Mucobromic and mucochloric acid were used as building blocks for the construction of a chemical combinatorial library of 3,4,5-trisubstituted 2(5H)-furanones. With these 2 butenolide building blocks, and eight alcohols a sublibrary of 16 dihalogenated 5-alkoxy-2(5H)-furanones was prepared. This sublibrary of 5-alkoxylated furanones was reacted with 16 amines generating a full size focussed combinatorial library of 256 individual compounds. This three dimensional combinatorial library of 3-halogen-4-amino-5-alkoxy-2(5H)-furanones was prepared around the benzimida-zolyl furanone lead structure by applying a solution phase combinatorial chemistry concept. Typical representatives of the library were purified and fully characterized and one x-ray structures was recorded, additionally. The 3-bromo-4-benzimizazolyl-5-methoxy-2(5H)furanone, Br-A-l, showed an MIC of 8 microg/ml against the multiresistant Staphylococcus aureus (MRSA).

Anti-Bacterial Agents↗
PubMed2003

Remote site bromination via a cascade rearrangement involving two bridging dioxonium species during oxidative cleavage of a benzylidene acetal.

Attempted cleavage of the benzylidene group of 3,5-O-benzylidene-2,6,7-tri-O-trimethylacetyl-D-glycero-D-gulo-heptono-1,4-lactone with N-bromosuccinimide led to the formation of a 7-bromo derivative with a benzoyl group in the 3-position and trimethylacetyl groups in the 5 and 6 positions. Analysis of the coupling constants in the proton NMR spectra indicated that both trimethylacetyl groups had participated to shift the crowded electron-deficient center formed at the 5-position by the decomposition of the bromobenzylidene group to the much more accessible 7-position. The net result of this cascade rearrangement was retention at both the C-5 and C-6 positions. This is an interesting example of a cascade rearrangement under strict entropic and stereo control the synthetic utility of which is being investigated.

Benzylidene Compounds↗
PubMed1988

Liquid chromatographic determination of diastereomeric glutathione conjugates and further derivatives of alpha-bromoisovalerylurea in rat bile and urine by electrochemically generated bromine.

To study the glutathione conjugation of alpha-bromoisovalerylurea in the rat in vivo, a reversed-phase liquid chromatographic assay of the thioether metabolites in bile and urine was developed. Since alpha-bromoisovalerylurea has a chiral centre, two diastereomeric glutathione conjugates (in bile) and two diastereomeric mercapturates (in urine) can be expected. The separation characteristics of these metabolites and the corresponding cysteine conjugates were investigated. Whereas all thioether metabolites could be separated in one run, optimal separation of the diastereomers required different mobile phases for the glutathione conjugates (in bile) and the mercapturates (in urine). The glutathione conjugates were analysed with the ion-pairing agent sodium decanesulphonate in the mobile phase, but the mercapturates were analysed without an ion-pair-forming agent. For detection, on-line generation of a constant bromine level (100%) was used; bromine-reactive compounds result in a decrease of the amperometric response from the 100% baseline. This technique could be used in continuous automated operation and required little clean-up of the sample. Thus, the diastereomeric glutathione conjugates and mercapturates were quantified in rat bile and urine samples, respectively, by direct injection of the (centrifuged and diluted) samples on the column. The limit of determination of the respective metabolites was 9 and 2.6 ng in bile and urine, respectively. Incubation mixtures of alpha-bromoisovalerylurea with a rat liver cytosolic fraction or with isolated rat hepatocytes were chromatographed after deproteinization with a double volume of methanol. The limit of determination of the diastereomeric glutathione conjugates in the deproteinized incubation samples was 2.0 ng.

Animals↗
PubMed2006

A competitive molecular recognition study: syntheses and analysis of supramolecular assemblies of 3,5-dihydroxybenzoic acid and its bromo derivative with some N-donor compounds.

A molecular recognition study of 3,5-dihydroxybenzoic acid (1) and its bromo derivative 4-bromo-3,5-dihydroxybenzoic acid (2) with the N-donor compounds 1,2-bis(4-pyridyl)ethene (bpyee), 1,2-bis(4-pyridyl)ethane (bpyea), and 4,4'-bipyridine (bpy) is reported. Thus, the syntheses and structural analysis of molecular adducts 1 a-1 c (1 with bpyee, bpyea, and bpy, respectively) and 2 a-2 c (2 with bpyee, bpyea, and bpy, respectively) are discussed. In all these adducts, recognition between the constituents is established through either O--H...N and/or O--H...N/C--H...O pairwise hydrogen bonds. In all the adducts both OH and COOH functional groups available on 1 and 2 interact with the N-donor compounds, except in 2 a, in which only COOH (COO-) is involved in the recognition process. The COOH moieties in 1 a, 1 b, and 2 b form only single O--H...N hydrogen bonds, whereas in 1 c and 2 c, they form pairwise O--H...N/C--H...O hydrogen bonds. In addition, subtle differences in the recognition patterns resulted in the formation of cyclic networks of different dimensions. In fact, only 1 c forms a four-molecule cyclic moiety, as was already documented in the literature for this kind of assemblies. All complexes have been characterized by single-crystal X-ray diffraction. The supramolecular architectures are quite elegant and simple, with stacking of sheets in all adducts, but a rather complex network with a threefold interpenetration pattern was found in 2 c.

Bromine Compounds↗
PubMed1990

Characterization of vanadium bromoperoxidase from Macrocystis and Fucus: reactivity of vanadium bromoperoxidase toward acyl and alkyl peroxides and bromination of amines.

Vanadium bromoperoxidase (V-BrPO) has been isolated and purified from the marine brown algae Fucus distichus and Macrocystis pyrifera. V-BrPO catalyzes the oxidation of bromide by hydrogen peroxide, resulting in the bromination of certain organic acceptors or the formation of dioxygen. V-BrPO from F. distichus and M. pyrifera have subunit molecular weights of 65,000 and 74,000, respectively, and specific activities of 1580 units/mg (pH 6.5) and 1730 units/mg (pH 6) for the bromination of monochlorodimedone, respectively. As isolated, the enzymes contain a substoichiometric vanadium/subunit ratio; the vanadium content and specific activity are increased by addition of vanadate. V-BrPO (F. distichus, M. pyrifera, and Ascophyllum nodosum) also catalyzes the oxidation of bromide using peracetic acid. In the absence of an organic acceptor, a mixture of oxidized bromine species (e.g., hypobromous acid, bromine, and tribromide) is formed. Bromamine derivatives are formed from the corresponding amines, while 5-bromocytosine is formed from cytosine. In all cases, the rate of the V-BrPO-catalyzed reaction is much faster than that of the uncatalyzed oxidation of bromide by peracetic acid, at pH 8.5, 1 mM bromide, and 2 mM peracetic acid. In contrast to hydrogen peroxide, V-BrPO does not catalyze formation of dioxygen from peracetic acid in either the presence or absence of bromide. V-BrPO also uses phenylperacetic acid, m-chloroperoxybenzoic acid, and p-nitroperoxybenzoic acid to catalyze the oxidation of bromide; dioxygen is not formed with these peracids. V-BrPO does not catalyze bromide oxidation or dioxygen formation with the alkyl peroxides ethyl hydroperoxide, tert-butyl hydroperoxide, and cuminyl hydroperoxide.

Amines↗
PubMed2004

Product study of the gas-phase BrO-initiated oxidation of Hg0: evidence for stable Hg1+ compounds.

Mercury is a key toxic environmental pollutant, and its speciation affects its bioavailability. BrO radicals have been identified as key oxidants during mercury depletion events observed in Arctic and sub-Arctic regions. We report the first experimental product study of BrO-initiated oxidation of elemental mercury at atmospheric pressure of ca. 0.987 bar and T= 296+/-2 K. We used chemical ionization and electron impact mass spectrometry, gas chromatography coupled to a mass spectrometer, a MALDI-TOF mass spectrometer, a cold vapor atomic fluorescence spectrometer, and high-resolution transmission electron microscopy coupled to energy dispersive spectrometry. BrO radicals were formed using visible and UV photolysis of Br2 and CH2Br2 in the presence of ozone. We have analyzed the products in the gas phase, on suspended aerosols and on wall deposits, and identified HgBr, HgBrO/HgOBr, and HgO as reaction products. Mercury aerosols with a characteristic width of ca. 0.2 microm were observed as products. We herein discuss the implications of our results to the chemistry of atmospheric mercury and its potential implications in the biogeochemical cycling of mercury.

Atmosphere↗
PubMed2006

Toxic effects of brominated indoles and phenols on zebrafish embryos.

Organobromine compounds in the marine environment have been the focus of growing attention in past years. In contrast to anthropogenic brominated flame retardants, other brominated compounds are produced naturally, e.g., by common polychaete worms and algae. Brominated phenols and indoles assumed to be of biogenic origin have been detected in water and sediment extracts from the German Bight. These substances as well as some of their isomers have been tested with the zebrafish embryo test and were found to cause lethal as well as nonlethal malformations. The zebrafish test was able to detect a log K(OW)-related toxicity for bromophenols, suggesting nonpolar narcosis as a major mode of action. Different effect patterns could be observed for brominated indoles and bromophenols. The comparison of effective concentrations in the zebrafish embryo test with the concentrations determined in water samples suggests the possibility that brominated indoles may affect early life stages of marine fish species in the North Sea.

Animals↗
PubMed2006

Identification and quantification of polybrominated hexahydroxanthene derivatives and other halogenated natural products in commercial fish and other marine samples.

During routine analysis of commercial fish on halogenated pollutants, an unknown tribromo component (TriBHD) was initially detected as an abundant peak in sample extracts from the Mediterranean Sea. The molecular formula was established to be C16H19Br3O by gas chromatography with electron ionization high-resolution mass spectrometry (GC/EI-HRMS). GC/EI-MS data were virtually identical with a polybrominated hexahydroxanthene derivative (PBHD) previously isolated from an Australian sponge species known to occur in the Mediterranean Sea as well. A tetrabromo isomer (TetraBHD) was also found in the fish samples. The concentrations of TriBHD and other halogenated compounds in commercial fish (sea bass, gilt head bream, anchovy, sardine, and salmon) were estimated with GC/electron capture detection (ECD). Using the ECD response of trans-nonachlor, the concentration of TriBHD reached up to 90 ng/g lipid weight and accounted for up to >90% of the concentration of p,p'-DDE, which was the most abundant peak in the most samples investigated. On the basis of the GC/ECD response, TetraBHD amounted for approximately 1/7 of TriBHD in all fish samples investigated. The sample with the highest content was a green-lipped mussel from New Zealand (236 ng/g lipid weight). The halogenated natural products TBA, Q1, and MHC-1 were also present in most of the samples. We assume that the bulk of the residues in fish from aquaculture may originate from algae and sponges living in proximity of the fish farms. Detection of TriBHD and TetraBHD in blubber of a monk seal (Monachus monachus) suggests that both HNPs may reach the top predators of food webs and thus also humans.

Animals↗
PubMed2000

[Syntheses of biologically active natural products using metal-mediated reactions as key reactions].

This review deals with total syntheses of biologically active natural products by the use of metal-mediated coupling reactions as key steps. First, we explored the coupling reactions mediated by samarium (II) diiodide (SmI2), which is a useful versatile one electron reducing reagent. The SmI2-mediated coupling reactions of N,N-dibenzyl-alpha-bromoamide and N,N-bis(p-methoxyphenyl)-alpha-bromoamide with carbonyl compounds gave the corresponding beta-hydroxyamides, respectively. Then, oxidative treatment of compound 6c with ceric (IV) ammonium nitrate (CAN) gave d,l-myrmicacine (7b). Synthesis of pyrrolizidine alkaloid pyrrolam A (8), which causes damage to fertilized eggs at a low concentration, was accomplished via the SmI2-mediated cyclization between a bromoalkyl and ynamide group. Next, (+/-)-oxerine (15), a monoterpene alkaloid, was synthesized starting from 3-bromopyridine. The synthesis of (+/-)-oxerine (15) was also carried out via the SmI2-mediated intramolecular cyclization of gamma-ethynyl bromide (40). Next, we focused on the palladium-catalyzed oxidation of alcohol and tried to expand it to the intermolecular cyclization. As a result, treatment of hydroxy-enamines and hydroxy-amines with a palladium catalyst gave the corresponding pyrroles and indoles in moderate to good yields. Finally, the syntheses of three pyrrolidine alkaloids were described. The chromium (II) chloride-mediated coupling reactions of (R)- and (S)-Garner aldehydes (56 and 57) with allyl bromides proceeded with moderate stereoselectivity to afford the corresponding homoallyl alcohols, which were converted to (2R, 3S)-2-hydroxymethyl-3-hydroxypyrrolidine (61), (2R, 3R, 4R)-3-hydroxy-4-methylproline (66), and the enantiomer (77) of (-)-bulgecinine (78).

Bromine Compounds↗
PubMed2002

Identification of oxidized methionine residues in peptides containing two methionine residues by derivatization and matrix-assisted laser desorption/ionization mass spectrometry.

Oxidation of methionine residues in peptides and proteins occurs in vivo or may be an artifact resulting from purification steps. We present a three step method for the localization of methionine sulfoxides in peptides with two methionine residues. In the first step, the N-terminus as well as other reactive side chain functions are blocked by acetylation. The resulting protected peptides are cleaved by cyanogen bromide. The cleavage does not occur at methionine sulfoxide but only at reduced methionine residues forming new amino termini. The newly formed amino group is then derivatized with a bromine containing compound in the last step of the procedure. The resulting peptide can easily be identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry using both the characteristic isotope pattern of the halogen and the metastable loss of methanesulfenic acid from oxidized residues. This procedure allows the unequivocal localization of oxidized methionines even in complex peptide mixtures.

Amino Acid Sequence↗