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[reaction: see text] We developed Hg(OTf)2-catalyzed cyclization of (E)-1,3-dimethoxy-5-(4-methyl-3-nonen-7-ynyl)benzene leading to the formation of (4aS,10aS)-3,4,4a,9,10,10a-hexahydro-5,7-dimethoxy-1,4a-dimethylphenanthrene in 98% yield with up to 100 catalytic turnovers. This is the first mercuric salt-catalyzed biomimetic tandem cyclization.
[reaction: see text] Abyssomicins, a novel class of polyketide antibiotics, are characterized by an unprecedented spirotetronic tricyclic subunit in their structure. In this letter, a short synthesis of a suitably functionalized tricyclic precursor of abyssomicins is reported. Key steps of the synthesis are (i) the highly stereoselective Al(III)-tethered Diels-Alder reaction and (ii) the tandem Dieckmann cyclization/TBS trapping of the C9 hydroxyl group followed by a regioselective intramolecular epoxide opening for the assembly of the target tricyclic structure.
The hepatic microsomal metabolites of the highly carcinogenic dimethylbenzacridines, 7,9-dimethylbenz[c]acridine (7,9-DMBAC), and 7,10-dimethylbenz[c]acridine (7,10-DMBAC) were obtained with preparations from 3-methylcholanthrene-pretreated rats. Metabolites were separated by reversed-phase HPLC and characterized using UV spectral data and chemical ionization-mass spectrometry after trimethylsilylation and GC. Comparisons with products formed in the presence of the epoxide hydrolase inhibitor, 1,1,1-trichloropropane 2,3-oxide and with those formed from the three synthetic alcohol derivatives of each parent compound, aided the assignment of firm or tentative structures to 16 products from 7,9-DMBAC found in 22 reversed-phase chromatographic peaks, and for 17 products of 7,10-DMBAC found in 19 chromatographic peaks. The more abundant metabolites were derived from oxidation of the methyl groups. Other metabolites were dihydrodiols, epoxides, phenols and secondary metabolites. The 9-methyl group prevented dihydrodiol formation at the 8,9-position from 7,9-DMBAC, and for each carcinogen, the 3,4-dihydrodiol was formed. As well, 3,4-dihydrodiols of methyl oxidized compounds were found.
The methylene-C(14) group is hydroxylated yielding formate-C(14) in the microsome-reduced nicotinamide-adenine dinucleotide phosphate system in vitro and yielding expired C(14)O(2), in living mice and houseflies. Methylenedioxyphenyl compounds apparently serve as alternate substrates for this enzymatic hydroxylation system of microsomes, and thus reduce the rate of metabolism and prolong the action of certain drugs and insecticide chemicals.
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A reversed phase HPLC method has been investigated in order to resolve three main pentacyclic triterpene acids (oleanolic-, betulinic- and ursolic acid) found in a lot of plants. Some of them (oleanolic and ursolic acids) are position isomers and their resolution is highly improved by the addition of derivatized cyclodextrins in mobile phase. The formation of 1:1 inclusion complexes was assumed. Apparent formation constants of triterpene acids with DM-beta-CD and HP-gamma-CD were determined by HPLC method. Experimental results confirmed the complexation model and explained the modification of elution order according to the type of cyclodextrin added to the mobile phase. The influence of mobile phase organic modifier on apparent formation constants was also investigated. Results proved the competition between cyclodextrins hydrophobic cavity and organic solvent towards triterpene acids affinity.
During April and May 1985, some emission samples from private coal firing (domestic fuel) were taken and were fired with two different kind of coal (bituminous and brown coal). Also, measurements were done under different combustion conditions (low and high concentrations of oxygenium during the combustion process). In June and November 1985, some emission samples from heavy diesel-engines were taken in a special tunnel equipment, at different engine conditions. During September 1985, also suspended particulates in a highway traffic tunnel were taken. All these samples were taken using high volume cascade impactors which give a fractionation of the suspended particulates into different particle sizes, according to their retention behaviour in the human respiratory system. The results of these emission samples and samples in the highway tunnel were compared with prior immission measurements of urban suspended particulates in Berlin-West, during January 1984. The etherextractable organic matter (= EEOM) of the total suspended particulate matter (= TPM) was determined using ultrasonic extraction method. The EEOM was separated into an acidic (= AF), a basic (= BF) and a neutral fraction (= NF) by dissolution in acidic and basic agents. Of the neutral fraction (NF), further separation was done into aliphatic compounds (= AIP), polycyclic aromatic hydrocarbons (= PAH) and polar neutral organic compounds (POCN) by using thin layer chromatography. From the PAH and POCN, single compounds were identified by gas chromatographic analysis with dual capillary collumns and internal standard method. All organic fractions were tested to their mutagenic activity in the Salmonella typhimurium mammalian microsome bioassay by Ames. The following results were gained: the neutral fraction (NF) made the highest part of the EEOM (greater than or equal to 60%) whereas the part of the AF amounted to 10-25% and of the basic fraction (BF) to approximatively 5-20%. Making further separation of the NF, some differences between the emission sources were gained. Now, the AIP amounted to a percentage of ca. 15% of the NF for coal firing emissions and to ca. 20-40% for diesel-emissions and samples in the highway tunnel. The percentages of the PAH and POCN varied in dependence of the combustion conditions on both emission sources and amounted to 20-50% for the PAH and 30-50% for the POCN. The gas chromatographic analysis showed also differences between the two emission sources. So, for coal firing emissions, higher concentrations for phenanthrene, benzo(a)-pyrene and dibenz(a.h)anthracene (for PAH) and 9-fluorenone (for POCN) were gained.(ABSTRACT TRUNCATED AT 400 WORDS)
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Diesel particulate matter (DPM) has been recognized as carcinogenic due to its respirable sizes and toxic compositions. It is essential to understand its formation mechanisms to effectively reduce DPM emissions. Studies have indicated that resonance stabilize radicals can result in more soot and PAC (polycyclic aromatic compounds) formation in combustion processes. As the largest single polycyclic aromatic constituent in petroleum fuels, 1- and 2-methylnaphthalenes can readily form resonance-stabilized radicals in combustion, and yet the reaction mechanisms are not well understood. In this paper, product formation mechanisms of these compounds are experimentally investigated in a flow reactor. The pyrolysis of 1- and 2-methylnaphthalene was studied from 800 to 1000 degrees C, and the oxidation of 2-methylnaphthalene was studied from 650to 950 degrees C. The PACs were quantified by GC/MS and HPLC, and soot was quantified gravimetrically. Naphthalene is the most abundant product and is formed from methyl loss by H displacement. Isomerization in pyrolytic conditions results in the second most abundant product. The methyl radicals recombine with the reactants to form ethylnaphthalenes and dimethylnaphthalenes. 2-Naphthaldehyde is formed from the oxidation of the naphthylmethyl radicals. 1-Methylnaphthalene is of slightly higher reactivity in comparison to its isomer. The experimental results indicate that the PAC formation from the pyrolysis and oxidation of the two methylnaphthalenes are likely to be governed by similar mechanisms. The lack of carbon dimerization products in significant quantities may be due to their further growth into soot.
The title compound, which belongs to a new synthetic group of polycyclic lactones derived from isocoumarin, exhibits a remarkably high degree of carcinogenicity in situ when injected in mice. Cancer-inducing activity has also been found in similar isocoumarins, a family known to include many naturally occurring substances.
Copper phthalocyanine trisulfonate (cpt) is known to form complexes with polycyclic planar compounds and for that reason has been used in a rayon fiber supported form as a ligand to selectively trap polycyclics, e.g., mutagenic/carcinogenic heterocyclic amines and polycyclic hydrocarbons. With the rayon-supported ept, batch-wise treatment is employed in the adsorption of polycyclic mutagens from samples such as an aqueous extract of food, river water, and human urine. We have now found that chitin (poly-N-acetylglucosamine) powder bearing covalently linked cpt residues is suitable for preparing a short packed column through which a sample solution may be passed. The derivatization of chitin to fix the ept ligand on the hydroxyl groups with the use of Reactive Blue 21 proceeded more rapidly than that of the cellulose supports, and the resulting cpt-chitin showed a ept content of 44 mol/g, a content twofold greater than that of cpt-rayon and fourfold greater than that of cpt cellulose prepared under equivalent conditions. A sample of ept-chitin (0.12 g) was placed in a Sep-Pak cartridge case, and the column was tested for its utility. Compounds, mostly mutagens, having structures of three or more fused rings (aflatoxin B1, IQ, PhIP, and six others tested) were efficiently adsorbed (>85%) to the column when their 104106 M buffered solutions (5 ml, pH 7) were passed through it (flow rate, 510 mI/mm). Compounds with fewer than three rings (eight compounds tested) flowed through the column with little or no adsorptions. The adsorbed compounds can be eluted with a mixture of methanol and concentrated ammonia. This technique was successfully applied for concentrating mutagenic components from Beef Extract and river water. The method is superior to the previous methods in terms of selectivity and high recovery for polycyclics. Simplicity and a less time-consuming nature of manipulation are advantageous.
The mutagenic activity bioassay Mutatox was used to assess the mutagenic activity associated with sediments collected from five UK estuaries. Assays were performed on extracts of sediment pore water and residual particulate material isolated from sediment samples collected from the rivers Tyne, Tees, Mersey, and Thames as well as Southampton Water. No mutagenic activity was associated with the pore water extracts, however, 7 of the 28 organic solvent extracts of sediment particulate material contained potential genotoxins. By using Mutatox in association with bioassay-directed fractionation, attempts were made to identify the mutagenic compounds present in the extracts. The fractionation procedure used normal phase solid phase extraction, C18 reverse phase HPLC and cyano/amino bonded silica normal phase HPLC. GC-MS (EI and NICI) analysis was used to identify polycyclic aromatic hydrocarbons (PAH), alkyl substituted PAH, nitro-polycyclic aromatic compounds (nitro-PACs), polycyclic aromatic ketones, oxygenated-PACs, and other known mutagens contributing to the genotoxicity measured in the samples. Some potentially genotoxic compounds remain unidentified.