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Cr(III) complexes of tridentate SNS ligands have been prepared and evaluated as catalysts for ethylene trimerization, with several giving very high activity and excellent selectivity toward 1-hexene when activated with methylaluminoxane. The new complexes illustrate the potential of sulfur-based ligands on early transition metals for catalysis.
An entirely new naphthalene having one six-membered ring, whose bond lengths are equalized, and another ring, whose bond lengths are alternated, has been prepared via one-electron oxidation of a benzene annelated with three bicyclo[2.1.1]hexene units. The structure has been determined by X-ray crystallography and the aromaticity of two benzene rings estimated by theoretical calculations. Although the former six-membered ring has a higher degree of aromaticity, it has been found to be more reactive toward singlet oxygen owing to the greater strain contained in it. These results have been interpreted by means of theoretical calculations.
For the first time, the L-proline-catalyzed direct asymmetric self-aldolization of acetaldehyde is described affording (+)-(5S)-hydroxy-(2E)-hexenal 2 with ee's ranging from 57 to 90%. Further transformations of 2 into synthetically valuable building blocks are presented. A mechanism for the formation of 2 is proposed.
Lewis acids can efficiently promote free radical atom transfer reactions of an oxazolidinone imide substrate, 1, derived from alpha-bromo acetic acid. Thus, 1 undergoes a radical chain addition to 1-hexene giving the atom transfer addition compound, 6, in the presence of scandium or ytterbium triflate in 1,2-dichloroethane or a cosolvent mixture of 1/9 THF/dichloromethane. In 1,2-dichloroethane the solution is heterogeneous, while the cosolvent mixture gives a homogeneous solution, even at temperatures of -78 degrees C. Competition experiments were carried out in both solvent systems with added carbon tetrachloride to study how Lewis acid affected the product distribution. In the presence of carbon tetrachloride, chloride 7 is formed in addition to 6 and the ratio of these two products depends on the amount of Lewis acid present. In the presence of ytterbium triflate, in the cosolvent system, the reaction rate of bromine atom transfer was enhanced up to 400-fold compared to the reaction without added Lewis acid. Significant rate enhancements were also obtained in the solvent 1,2-dichloroethane, although the analysis of the system is complicated by the heterogeneous nature of the medium. Computation of C-Br bond dissociation energies (BDE) of the complexed and uncomplexed oxazolidinone bromide suggest that complexation lowers the BDE due to the effect of the strong electron-withdrawing group on the C-Br bond dipole.
Various 2-(6-substituted 3(Z)-hexen-1,5-diynyl)anilines 1a-g were treated with potassium tert-butoxide or potassium 3-ethylpentanoxide in NMP at 60 degrees C for 2 h to give the corresponding 5-substituted carbazoles 2a-g in 36-65% yields together with indoles 9a-g in 21-40% yields, respectively. Exposing the trifluoroacetamide analogues 10h-k under the same reaction conditions gave the carbazoles 2b-e in 37-57% yields and indoles 9b-e in 15-27% yields. Subsequent cyclizations of acetamide analogues 10a-g gave carbazoles 2a-g in 53-86% yields.
[reaction: see text] Treatment of 6-iodo-1-hexene derivatives with trimethylsilylmethyl Grignard reagent in the presence of CoCl(2)(dppb) in refluxing THF affords Heck-type products, methylenecyclopentanes, in good yields.
A novel cyclooctatetraene (COT) radical cation fully annelated with bicyclo[2.1.1]hexene units was prepared as SbCl(6)(-) salt, and planarity of the octagonal ring was clarified by ESR and theoretical calculations. Its longest wavelength absorption (630 nm) is blue-shifted from that (745 nm) of COT radical cation annelated with bicyclo[2.2.2]octene units due to the widening of the HOMO-SOMO gap accompanying the flattening of the COT ring. [structure: see text]
We searched for mutagens that react with 2'-deoxyguanosine (dGuo) in model systems of lipid peroxidation. To autoxidation systems of methyl linoleate (model of omega-6 fat), methyl alpha-linolenate (MLN) (model of omega-3 fat), and commercial salad oil, dGuo was added. The reaction mixtures were analyzed by HPLC. Six adducts were detected, and their structures were determined by 1H and 13C NMR, UV, and mass spectra and by comparison with synthetic authentic samples. The mutagens that reacted with dGuo to form these adducts were proposed as glyoxal, glyoxylic acid, ethylglyoxal, and 4-oxo-2-hexenal (4-OHE). The formation of 8-hydroxy-dGuo, an oxidized product of dGuo, was also detected in the model reaction mixtures. Among them, glyoxal and glyoxylic acid are known mutagens, while ethylglyoxal and 4-OHE, produced from MLN, have not been reported as mutagens thus far. We confirmed the mutagenic activity of 4-OHE with Salmonella strains, TA100 and TA104, without S9 mix. These compounds may be involved in lipid peroxide-related cancers.
Whereas the rates of propene polymerisation catalysed by zirconocene ion pairs are strongly anion-dependent, hexene polymerisations are not; the findings demonstrate the existence of very different kinetic regimes for two closely related reactions.
This study describes the synthesis of 6 -phenyl-3-hexen-2-one, a proposed metabolite of kava-kava (kava, 'Awa, Yaqona, Piper methysticum Forst.), its reactivity with glutathione in vitro, and its isolation and identification, as its mercapturic acid adduct using LC/MS/MS, in the urine of two human subjects following their ingestion of kava. A possible metabolic pathway for the formation of this metabolite and its possible role in hepatotoxicity are also discussed.
The CYP74B2 gene in Arabidopsis (Arabidopsis thaliana) ecotype Columbia (Col) contains a 10-nucleotide deletion in its first exon that causes it to code for a truncated protein not containing the P450 signature typical of other CYP74B subfamily members. Compared to CYP74B2 transcripts in the Landsberg erecta (Ler) ecotype that code for full-length hydroperoxide lyase (HPL) protein, CYP74B2 transcripts in the Col ecotype accumulate at substantially reduced levels. Consistent with the nonfunctional HPL open reading frame in the Col ecotype, in vitro HPL activity analyses using either linoleic acid hydroperoxide or linolenic acid hydroperoxide as substrates show undetectable HPL activity in the Col ecotype and C6 volatile analyses using leaf homogenates show substantially reduced amounts of hexanal and no detectable trans-2-hexenal generated in the Col ecotype. P450-specific microarrays and full-genome oligoarrays have been used to identify the range of other transcripts expressed at different levels in these two ecotypes potentially as a result of these variations in HPL activity. Among the transcripts expressed at significantly lower levels in Col leaves are those coding for enzymes involved in the synthesis of C6 volatiles (LOX2, LOX3), jasmonates (OPR3, AOC), and aliphatic glucosinolates (CYP83A1, CYP79F1, AOP3). Two of the three transcripts coding for aliphatic glucosinolates (CYP83A1, AOP3) are also expressed at significantly lower levels in Col flowers.
Combinations of polymyxins and phytochemicals were tested for antimicrobial activity against two gram-negative bacteria. Various degrees of potentiation were found against Pseudomonas aeruginosa and Escherichia coli with (E)-2-hexenal and indole. Three-compound combinations were found to further increase the activity of polymyxin B sulfate and colistin methanesulfonate against both bacteria. Combinations with colistin against P. aeruginosa resulted in the highest degree of potentiation, with a 512-fold increase in colistin antimicrobial activity. These results indicate the potential efficacy of phytochemical combinations with antibiotics to enhance total biological activity.
Poly(maleic anhydride-alt-hexen-1)(poly(MA-alt-H-1)) has been synthesized by radical polymerization and characterized by DSC, FT-IR, acid number determination, viscometric and NMR methods. Data showed that the co-polymer is an alternating co-polymer whose composition does not depend on the monomer feed composition. Invertase was immobilized onto a poly(MA-alt-H-1) membrane via glutaraldehyde and bovine serum albumin. The Km value of poly(MA-alt-H-1)-invertase was approximately 4.4-fold higher than the free enzyme, indicating decreased affinity by the invertase for its substrate (sucrose), whereas Vmax was lower for the immobilized invertase. Immobilization improved the pH stability of the enzyme, as well as its temperature stability. Immobilized samples obtained were stable and could be used many times over a period of 2 months without considerable activity loss.
In the present study, to investigate the contribution of n-3 PUFAs in the oxidative modification of protein in vivo, we characterize the covalent binding of 4-hydroxy-2-hexenal (HHE), a potent cytotoxic aldehyde originating from the peroxidation of n-3 PUFAs, to protein and describe the production of this aldehyde in oxidatively modified LDL and in human atherosclerotic lesions. Upon incubation with BSA, HHE was rapidly incorporated into the protein and generated the protein-linked carbonyl derivative, a potential marker of oxidatively modified proteins under oxidative stress. To detect the protein-bound HHE in vivo, we raised monoclonal antibody HHE53 (MAb HHE53) directed to the HHE-modified protein and identified the Michael addition-type HHE-histidine adduct as the major epitope. This antibody reacted with copper-oxidized LDL, suggesting that HHE was produced during the oxidative modification of LDL. In addition, we demonstrated that the materials immunoreactive to MAb HHE53 indeed constituted the atherosclerotic lesions, in which intense positivity was associated primarily with macrophage-derived foam cells. The results of this study suggest that the reaction between oxidized n-3 PUFAs and protein might represent a process common to the formation of degenerative proteins during aging and its related diseases.
Changes in the 4-hydroxy-2-hexenal (HHE) and malonaldehyde (MA) contents were investigated in the meat of the yellowtail Seriola quinqueradiate containing 0, 0.3, 0.6, and 0.9 M NaCl stored at 0 degrees C for 7 days. After 7 days of storage, the HHE content was significantly lower and the MA content significantly higher in the meat containing NaCl than in the control without NaCl.
The relationships between the chemical structures and the odor characteristics were examined on a series of highly purified n-hexenols and n-hexenals-(14 isomers). The C6-enals and the corresponding alcohols resembled in odor characteristics each other. However, the odor strength of the aldehydes was 100-1000 times higher than those of the alcohols. In the principal components analysis, the position of carbon-carbon double-bond in the C6-compounds was closely related to the scores of the first principal component, whereas the functional groups, hydroxy and formyl groups, were related to those of the second principal component except for (Z)-3-hexenol.
Patterns of hemoproteins turnover were studied in microsomal and mitochondrial fractions of liver tissue of guinea pigs with various duration of hexenal sleep; these patterns were calculated by means of modified procedure involving incorporation of 14C-aminolevulinic acid. Increase in turnover of microsomal cytochromes corresponded to decrease of their content in animals with short-term sleep simultaneously with a decrease in the lethal index after sensitization by means of ovalbumin.
The effects of trimethyl 3,3-N-hexene-5-lactam (T. H. L.) on the mechanical properties of longitudinal muscle strips of the distal rat colon were investigated through stretching, electrical stimulation and addition of pharmacologic agents. T. H. L. abolished the contraction induced by electrical stimulation and decreased amplitude of contractions induced by carbamoylcholine and serotonin. It further reduced the relaxation induced by adrenaline.