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Results for “Alkenes”

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At least 19 recordsLinked to original sources

PubMed2004

Reaction of gold(III) oxo complexes with alkenes. Synthesis of unprecedented gold alkene complexes, [Au(N,N)(alkene)][PF6]. Crystal structure of [Au(bipy(ip))(eta2-CH2=CHPh)][PF6] (bipy(ip) = 6-isopropyl-2,2'-bipyridine).

Gold alkene complexes [Au(bipyR)(eta2-alkene)][PF6] (bipyR = 6-alkyl-2,2'-bipyridine) have been obtained by reaction of gold(III) oxo complexes [Au2(bipyR)2(mu-O)2][PF6]2 with alkenes. The crystal structure of the styrene adduct [Au(bipy(ip))(eta2-CH2=CHPh)][PF6] (bipy(ip) = 6-isopropyl-2,2'-bipyridine) has been solved by X-ray analysis.

Journal Article↗

PubMed1992

Cometabolic degradation of chlorinated alkenes by alkene monooxygenase in a propylene-grown Xanthobacter strain.

Propylene-grown Xanthobacter cells (strain Py2) degraded several chlorinated alkenes of environmental concern, including trichloroethylene, 1-chloroethylene (vinyl chloride), cis- and trans-1,2-dichloroethylene, 1,3-dichloropropylene, and 2,3-dichloropropylene. 1,1-Dichloroethylene was not degraded efficiently, while tetrachloroethylene was not degraded. The role of alkene monooxygenase in catalyzing chlorinated alkene degradations was established by demonstrating that glucose-grown cells which lack alkene monooxygenase and propylene-grown cells in which alkene monooxygenase was selectively inactivated by propyne were unable to degrade the compounds. C2 and C3 chlorinated alkanes were not oxidized by alkene monooxygenase, but a number of these compounds were inhibitors of propylene and ethylene oxidation, suggesting that they compete for binding to the enzyme. A number of metabolites enhanced the rate of degradation of chlorinated alkenes, including propylene oxide, propionaldehyde, and glucose. Propylene stimulated chlorinated alkene oxidation slightly when present at a low concentration but became inhibitory at higher concentrations. Toxic effects associated with chlorinated alkene oxidations were determined by measuring the propylene oxidation and propylene oxide-dependent O2 uptake rates of cells previously incubated with chlorinated alkenes. Compounds which were substrates for alkene monooxygenase exhibited various levels of toxicity, with 1,1-dichloroethylene and trichloroethylene being the most potent inactivators of propylene oxidation and 1,3- and 2,3-dichloropropylene being the most potent inactivators of propylene oxide-dependent O2 uptake. No toxic effects were seen when cells were incubated with chlorinated alkenes anaerobically, indicating that the product(s) of chlorinated alkene oxidation mediates toxicity.

Alkenes↗

PubMed1997

Alkene monooxygenase from Xanthobacter strain Py2. Purification and characterization of a four-component system central to the bacterial metabolism of aliphatic alkenes.

Alkene monooxygenase from Xanthobacter strain Py2 is an inducible enzyme that catalyzes the O2- and NADH-dependent epoxidation of short chain (C2 to C6) alkenes to their corresponding epoxides as the initial step in the utilization of aliphatic alkenes as carbon and energy sources. In the present study, alkene monooxygenase has been resolved from the soluble fraction of cell-free extracts into four components, each of which has been purified to homogeneity, that are obligately required for alkene epoxidation activity. The four required components are 1) a monomeric 35.5-kDa protein containing 1 mol of FAD and a probable 2Fe-2S center; 2) a 13.3-kDa ferredoxin containing a Rieske-type 2Fe-2S cluster; 3) an 11-kDa monomeric protein that contains no detectable cofactors; and 4) a 212-kDa alpha2beta2gamma2 multimeric protein containing four atoms of nonheme iron. The 35.5-kDa protein has been characterized as an NADH reductase. The physiological electron acceptor for the reductase was the Rieske-type ferredoxin, which is proposed to be an intermediate electron carrier between the reductase and terminal catalytic component of the system. The 212-kDa protein was specifically inactivated in cell-free extracts by the mechanism-based inactivator propyne, suggesting that it is the catalytic component and contains the active site(s) for O2 activation and alkene epoxidation. The subunit structure and metal analysis of this component suggest that it contains two diiron centers, one for each alphabetagamma protomeric unit. No specific enzymatic activities could be assigned for the 11-kDa protein, but this component was obligately required for steady-state alkene epoxidation. The alkene monooxygenase components were expressed during growth of Xanthobacter Py2 on aliphatic alkenes or epoxides and repressed during growth on other carbon sources. The electron transfer components of alkene monooxygenase were highly specific: other reductase activities present in Xanthobacter were incapable of transferring electrons to the Rieske-type ferredoxin or substituting for the reductase in the alkene monooxygenase complex. Likewise, other bacterial and plant ferredoxins were unable to substitute for the Rieske-type ferredoxin in mediating electron transfer to the oxygenase. The biochemical properties of alkene monooxygenase described in this study suggest that this enzyme combines elements of both the well-characterized aromatic dioxygenase (two-component electron transfer scheme) and methane monooxygenase (small regulatory protein and diiron oxygenase) multicomponent enzyme systems.

Chromatography, Gel↗

PubMed1996

Oxygenation of (3Z)-alkenal to (2E)-4-hydroxy-2-alkenal in soybean seed (Glycine max L.).

(3Z)-Alkenals, such as (3Z)-hexenal and (3Z)-nonenal, are produced from polyunsaturated fatty acids via lipoxygenase and hydroperoxide lyase catalysis, but in soybeans (Glycine max L.) (3Z)-alkenals have a fleeting existence. In this study it was shown that soybean seeds possess two pathways that metabolize (3Z)-alkenals. One is a soluble (3Z):(2E)-enal isomerase that transformed (3Z)-hexenal and (3Z)-nonenal into the corresponding (2E)-alkenals. The other was a membrane-bound system that converted (3Z)-hexenal and (3Z)-nonenal into (2E)-4-hydroxy-2-hexenal and (2E)-4-hydroxy-2-nonenal, respectively. The latter conversion was shown to absorb O2 with a pH optimum of 9.5. Little effect observed with lipoxygenase inhibitors suggested that oxidation was not catalyzed by lipoxygenase. Instead, a specific (3Z)-alkenal oxygenase was implicated in forming intermediate alkenal hydroperoxides. Hydroperoxide-dependent peroxygenase (epoxygenase) is known to reduce hydroperoxides to their corresponding hydroxides and is also known to be inhibited by hydrogen peroxide preincubation. Consequently, intermediate 4-hydroperoxy-2-alkenals could be observed after inhibiting hydroperoxide-dependent peroxygenase by preincubation with hydrogen peroxide. Because 4-hydroxy-2-alkenals are potent toxins, these compounds may be produced as nonvolatile plant defensive substances.

Aldehydes↗

PubMed2006

1,1,2-Tris-organoselenide alkene derivatives, but not 1,2-bis-organoselenide alkene derivatives, inhibited delta-aminolevulinate dehydratase activity from human erythrocytic cells in vitro.

Organochalcogens are important intermediates and useful reagents in organic synthesis. Recent data from our laboratory demonstrated that bis and tris-selenide alkene derivatives are attractive synthetic targets because of their chemio-, regio- and stereo-selective reactions. Since the erythrocytic delta-aminolevulinate dehydratase (delta-ALA-D) activity could be an important indicator of toxicity, this report investigated bis and tris-selenide alkene derivatives effects on blood delta-ALA-D in vitro. To investigate the mechanisms by which these compounds inhibit human blood delta-ALA-D activity, a thiol reducing agent or zinc chloride were used. 1,2-Bis-selenide alkene derivatives 1a (R=4-MeOC(6)H(4)), 1b (R=4-ClC(6)H(4)) and 1c (R=2,4,6-Me(3)C(6)H(2)) did not inhibit human blood delta-ALA-D activity. 1,1,2-Tris-selenide alkene derivative 2a (R=C(6)H(5)) was the most potent delta-ALA-D inhibitor. Compounds 2b (R=4-MeOC(6)H(4)) and 2c (R=4-ClC(6)H(4)) displayed similar inhibitory potency towards delta-ALA-D activity. Dithiothreitol, a hydrophobic SH-reducing agent, was able to restore and to protect delta-ALA-D activity inhibited by tris-selenide alkene derivatives. Conversely, ZnCl(2) did not alter the enzyme inhibition induced by tris-selenide alkene derivatives. From these findings we suggest that 1,1,2-tris-selenide alkene derivatives inhibited delta-ALA-D activity by an interaction with essential sulfhydryl groups for the enzyme activity.

Alkenes↗

PubMed1996

Aliphatic and chlorinated alkenes and epoxides as inducers of alkene monooxygenase and epoxidase activities in Xanthobacter strain Py2.

The inducible nature of the alkene oxidation system of Xanthobacter strain Py2 has been investigated. Cultures grown with glucose as the carbon source did not contain detectable levels of alkene monooxygenase or epoxidase, two key enzymes of alkene and epoxide metabolism. Upon addition of propylene to glucose-grown cultures, alkene monooxygenase and epoxidase activities increased and after an 11-h induction period reached levels of specific activity comparable to those in propylene-grown cells. Addition of chloramphenicol or rifampin prevented the increase in the enzyme activities. Comparison of the banding patterns of proteins present in cell extracts revealed that polypeptides with molecular masses of 43, 53, and 57 kDa accumulate in propylene-grown but not glucose-grown cells. Pulse-labeling of glucose-grown cells with [35S]methionine and [35S]cysteine revealed that the 43-, 53-, and 57-kDa proteins, as well as two additional polypeptides with molecular masses of 12 and 21 kDa, were newly synthesized upon exposure of cells to propylene or propylene oxide. The addition to glucose-grown cells of a variety of other aliphatic and chlorinated alkenes and epoxides, including ethylene, vinyl chloride (1-chloroethylene), cis- and trans-1,2-dichloroethylene, 1-chloropropylene, 1,3-dichloropropylene, 1-butylene, trans-2-butylene, isobutylene, ethylene oxide, epichlorohydrin (3-chloro-1,2-epoxypropane), 1,2-epoxybutane, cis- and trans-2,3-epoxybutane, and isobutylene oxide stimulated the synthesis of the five propylene-inducible polypeptides as well as increases in alkene monooxygenase and epoxidase activities. In contrast, acetylene, and a range of aliphatic and chlorinated alkanes, did not stimulate the synthesis of the propylene-inducible polypeptides or the increase in alkene monooxygenase and epoxidase activities.

Alkenes↗

PubMed2006

Elevated levels of alkanals, alkenals and 4-HO-alkenals in plasma of hemodialysis patients.

BACKGROUND/AIMS: Several studies have implicated reactive carbonyl compounds (RCOs), especially those derived from lipid peroxidation, in the development of complications frequently associated with hemodialysis (HD) treatment. However, there is still much unknown regarding the nature and concentration of RCOs in HD patients. This study was designed to evaluate the level of toxic aldehydes in the plasma of HD patients and to determine the extent to which these aldehydes contribute to RCO toxicity among these patients. METHODS: 15 aldehydes of the alkanal, alkenal and 4-HO-alkenal type were measured in the plasma of 17 HD patients and 20 healthy controls. In addition, protein modification markers such as carbonyl content (CO), free thiol (SH) and residual free amino groups, as well as amyloid fibrils were also determined. RESULTS: 11 of the 15 aldehydes were significantly elevated in the HD group when compared with the controls. Correlation studies in the HD group revealed high relationships between total alkenals plus total 4-HO-alkenals versus CO, total alkanals versus NH2, total aldehydes versus SH, and total 4-HO-alkenals versus fibril. CONCLUSION: The increased levels of alkanals, alkenals and 4-HO-alkenals of lipid peroxidation in the plasma of HD patients may greatly contribute to the toxicity of RCOs. The pattern of modification of plasma protein by each group of aldehydes may provide new evidence on the in vivo mechanisms of toxicity triggered by these aldehydes on their target molecules.

Alkanes↗

PubMed2005

Palladium-catalyzed synthesis of 2,1'-disubstituted tetrahydrofurans from gamma-hydroxy internal alkenes. Evidence for alkene insertion into a Pd-O bond and stereochemical scrambling via beta-hydride elimination.

Palladium-catalyzed reactions of gamma-hydroxy internal acyclic alkenes with aryl bromides afford 2,1'-disubstituted tetrahydrofurans in good yields with diastereoselectivities of 3-5:1. The analogous transformations of substrates bearing internal cyclic alkenes afford fused bicyclic and spirocyclic tetrahydrofuran derivatives in good yields with excellent diastereoselectivities (>20:1). A series of deuterium labeling experiments indicate that the origin of the modest diastereoselectivity in reactions of acyclic internal alkene substrates likely derives from a series of reversible beta-hydride elimination and sigma-bond rotation processes that occur following a rare intramolecular alkene syn-insertion into an intermediate Pd(Ar)(OR) complex. In addition, these studies shed light on the chemoselectivity of insertion, suggesting that the alkene inserts into the Pd-O bond in preference to the Pd-C bond.

Alkenes↗

PubMed2003

Structural dependence of thermodynamics of alkene binding to yttrium alkyl complexes and of kinetics of alkyl migration to coordinated alkenes.

Agostic interactions in yttrium alkyls are structure dependent. Primary alkyl yttrium complexes have beta-CH(2) agostic interactions at low temperature, but a shift toward alpha-agostic interactions occurs on warming. For the more crowded beta-disubstituted yttrium alkyls, an alpha-CH(2) agostic interaction is seen. The thermodynamics of alkene binding to the primary alkyl yttrium complex Cp(2)YCH(2)CH(2)CH(CH(3))(2) (2) depend strongly on the structure of the alkene. A single allylic substituent on the alkene has a small effect on alkene binding, but a second allylic substituent has a large destabilizing effect. Propene binding to yttrium alkyls is largely independent of the nature of the alkyl ligand. Equilibrium constants for propene binding to n-, gamma-substituted, beta-substituted, and secondary alkyl yttrium complexes are similar. The rate of migration of an alkyl group to a coordinated alkene depends strongly on the structure of the alkyl group: n-alkyl approximately gamma-substituted >> beta-substituted >> alpha-substituted. The approximately 200-fold slower insertion of propene into Cp(2)YCH(2)CH(CH(3))(2) (6) than that into Cp(2)YCH(2)CH(2)CH(CH(3))(2) (2) is therefore due to kinetically slow migration of the beta-disubstituted alkyl group of 6 and not to differences in the equilibrium binding of propene. Processes related to chain transfer and site epimerization at the metal center are also reported.

Journal Article↗

PubMed1998

Lewis Acid Mediated Reactions of N-Arylsulfonimidoyl Chlorides with Alkenes. Some Steric Effects of Alkene Substitution.

The Lewis acid-mediated reaction of N-phenyl-S-(4-methylphenyl)sulfonimidoyl chloride with alkenes was explored in order to determine the effect of alkene substitution on the stereochemical outcome of the reaction. With monosubstituted alkenes, benzothiazines are produced with relatively low diastereoselection, with one unique exception, trimethylsilylethene. 1,1-Disubstituted alkenes give products with even lower stereoselectivity. With trisubstituted alkenes, steric effects begin to change the course the reaction from one which can be rationalized as a cycloaddition to one which seems to definitely produce a carbocationic intermediate. Interestingly, the stereoselection observed in the reaction of (E)- and (Z)-2-butenes shows large deviations from the norm with (E)-2-butene giving rise to two diastereomeric benzothiazines in a ratio of 45:1.

Journal Article↗

PubMed2006

Phosphabarrelenes as ligands in rhodium-catalyzed hydroformylation of internal alkenes essentially free of alkene isomerization.

Despite significant research efforts in the past, one of the remaining problems to be solved in industrially important hydroformylation is the chemoselective low-pressure hydroformylation of internal alkenes. We report here on a new class of phosphabarrelene/rhodium catalysts 2 that display very high activity towards hydroformylation of internal alkenes with an unusually low tendency towards alkene isomerization. Preparation of new phosphabarrelene ligands, studies of their coordination properties, as well as results obtained in the rhodium-catalyzed hydroformylation of cyclic and acyclic internal alkenes are reported.

Alkenes↗

PubMed2000

Oxygenation of (3Z)-alkenals to 4-hydroxy-(2E)-alkenals in plant extracts: a nonenzymatic process.

There is large interest in 4-hydroxy-(2E)-alkenals because of their cytotoxicity in mammals. However, the biosynthetic pathway for these compounds has not been elucidated yet. In plants, 4-hydroxy-(2E)-alkenals were supposed to be derived by the subsequent actions of lipoxygenase and a peroxygenase on (3Z)-alkenals. The presence of 9-hydroxy-12-oxo-(10E)-dodecenoic acid (9-hydroxy-traumatin) in incubations of 12-oxo-(9Z)-dodecenoic acid (traumatin) in the absence of lipoxygenase or peroxygenase, has prompted us to reinvestigate its mode of formation. We show here that in vitro 9-hydroxy-traumatin, 4-hydroxy-(2E)-hexenal and 4-hydroxy-(2E)-nonenal, are formed in a nonenzymatic process. Furthermore, a novel product derived from traumatin was observed and identified as 11-hydroxy-12-oxo-(9Z)-dodecenoic acid. The results obtained here strongly suggest that the 4-hydroxy-(2E)-alkenals, observed in crude extracts of plants, are mainly due to autoxidation of (3Z)-hexenal, (3Z)-nonenal and traumatin. This may have implications for the in vivo existence and previously proposed physiological significance of these products in plants.

Aldehydes↗

PubMed2005

Competition between alkenes in intramolecular ketene-alkene [2 + 2] cycloaddition: what does it take to win?

In the course of developing a new synthetic methodology using ketenes in sequential cycloaddition steps, we were faced with a competition problem with molecules containing a ketene tethered to more than one reacting partner. To pinpoint the electronic and tethering requirements for a chemoselective reaction, we undertook a series of ketene-alkene [2 + 2] cycloaddition competition experiments. Those experiments were conducted on molecules containing either two identical alkenes having different tether lengths or two alkenes having the same tether length but being electronically different. We demonstrated that the reaction is much faster for forming five-membered rings than six-membered rings and calculated the Hammett constant rho for intramolecular ketene-alkene [2 + 2] cycloadditions to be -1.39.

Journal Article↗

PubMed2002

[Alkene bromination used for detailed hydrocarbon and bulk hydrocarbon group-type analysis of gasolines containing alkenes].

The optimized reaction conditions of selective alkene bromination for gasolines containing aromatics and saturated hydrocarbons are presented. By this way, the interfering problem in alkene determination from coeluting saturated hydrocarbons has been solved. So the detailed hydrocarbon analysis can be improved by a simple system containing polar and non-polar columns or by a gas chromatograph coupled with an atomic emission detector (GC-AED). Under the optimized conditions, it was found that the alkene compounds were selectively and completely brominated but the aromatics and alkane compounds were remained unaffected. A simple treatment, 90 s-120 s for reaction and 10 s-20 s for removing the excess bromine, can be easily realized. The treatment is applied for the different types of gasoline containing 0-100% alkene. Besides, one of the most important applications of this treatment is to analyse the hydrocarbons in detail from the fluid catalytic cracking (FCC) gasoline. The samples in these cases may not be accurately analyzed when using the traditional method of hydrocarbon analysis because of the presence of coeluted interfering olefins above C7.

English Abstract↗

PubMed1986

Genotoxicity and cytotoxicity of selected pyrrolizidine alkaloids, a possible alkenal metabolite of the alkaloids, and related alkenals.

Recently our laboratory isolated trans-4-OH-2-hexenal from the hepatic microsomal metabolism of the macrocyclic pyrrolizidine alkaloid (PA) senecionine and demonstrated in vivo that hepatic necrosis occurred following injection into the hepatic portal vein. To demonstrate similarities in the toxic effects of these compounds, as well as additional macrocyclic PAs and alkenals, genotoxicity and cytotoxicity were examined in primary cultures of rat hepatocytes. A positive cytotoxic response was exhibited by senecionine, retrorsine, seneciphylline, 19-OH-senecionine, trans-4-OH-2-hexenal, trans-4-OH-2-nonenal, and nonenal as measured by the release of LDH. A weaker response was elicited by hexenal. Dosages used of each of these compounds ranged from 30 to 600 nmol/10(6) cells, with each compound exhibiting a linear dose response within this range. All eight compounds exhibited a positive, dose-related genotoxic response as measured by autoradiographic detection of unscheduled DNA synthesis. These results would predict a carcinogenic role for both the PAs and the alkenals. This would suggest similarities in the mechanisms of action of the PAs and alkenals, lending support to the proposed role of trans-4-OH-2-hexenal as an important toxic metabolite of the PAs.

Aldehydes↗

PubMed2001

Correlation of relative rates of PdCl(2) oxidation of functionalized acyclic alkenes versus alkene ionization potentials, HOMOs, and LUMOs.

Investigations of the title reaction, carried out by plotting logs of the relative reaction rates vs IPs, vs HOMOs, and vs LUMOs, reveal multiple nearly parallel lines of correlation with small negative slopes in each. Overall, the natural grouping into monosubstituted and disubstituted alkenes gives better correlations than that obtained by using all alkenes. Comparison with analogous plots for other reactions indicates that the mechanism for this reaction has similarities to that for hydroboration, the major difference being that the lines in the plots for hydroboration have positive slopes, indicating an electrophilic rate-determining step involving the pi electrons, while those for the title reaction have small negative slopes, indicating a nucleophilic rate-determining step. Of the two reaction mechanisms proposed for the title reaction, only one has a nucleophilic attack at the complexed alkene as the rate-determining step, and therefore, this work supports that reaction mechanism.

Journal Article↗

PubMed2006

New insight into reactions of Ni(S2C2(CF3)2)2 with simple alkenes: alkene adduct versus dihydrodithiin product selectivity is controlled by [Ni(S2C2(CF3)2)2]- anion.

The nickel bis(dithiolene) complex Ni(S2C2(CF3)2)2 employs its sulfur centers in reactions with alkenes, and stable interligand S-bonded alkene adducts can be formed. The present study shows that the selectivity of alkene binding to charge-neutral Ni(S2C2(CF3)2)2 is influenced by the anion [Ni(S2C2(CF3)2)2]-. In the absence of anion, formation of substituted dihydrodithiins (intraligand addition) dominates, whereas the presence of anion allows for the formation of stable interligand adducts. Mechanistic implications are discussed. The X-ray crystal structure of the ethylene adduct of Ni(S2C2(CF3)2)2 is presented, displaying interligand binding of ethylene to sulfur centers in the bis(dithiolene) complex.

Journal Article↗

PubMed1999

The Stille Reaction of 1,1-Dibromo-1-alkenes: Preparation of Trisubstituted Alkenes and Internal Alkynes.

The Stille reaction of 1,1-dibromo-1-alkenes 1 with aryl- and vinylstannanes produces different products depending on the reaction conditions. When the reaction is run in toluene or 1,4-dioxane with tris(2-furyl)phosphine (TFP) as the ligand, (Z)-bromoalkenes 2 are obtained stereospecifically in good to excellent yields with most substrates. However, 2-aryl-1,1-dibromo-1-alkenes (1e,1g) having an electron-donating methoxy group in the para- or ortho- position give poor yields. This method has been applied to the one-pot syntheses of stereospecifically trisubstituted alkenes 5. When the Stille reaction is conducted in a highly dipolar solvent (DMF), monobromides 2 and/or internal alkynes 4 are the products. The less reactive phenylstannane favors the formation of alkynes 4, regardless of which ligand is used. More reactive organostannanes (vinyl, furyl) require a very electron rich ligand, tris(4-methoxyphenyl)phosphine, for the formation of alkynes 4. This new method for internal alkyne preparation is general, requires very mild reaction conditions, and gives high yields.

Journal Article↗