Alkenyl Ethers Research Articles

Intramolecular dehydrohalogenation during base-mediated reaction of diols with dihaloalkanes.

Sodium alkoxides of a variety of diols were reacted with dibromoalkanes. It was found that the products of the reaction were alkenyl ethers resulting from intramolecular dehydrohalogenation of the initially formed monobromo ethers.

Pd(II) acts simultaneously as a Lewis acid and as a transition-metal catalyst: synthesis of cyclic alkenyl ethers from acetylenic aldehydes.

The reaction of carbon-tethered acetylenic aldehydes with alcohols in the presence of a catalytic amount of Pd(OAc)2 in 1,4-dioxane at room temperature gave the 5- or 6-membered acetal products in high yields. The 13C NMR studies suggested that a Pd(II) catalyst exhibited dual roles in the present reaction; the attack of ROH to aldehyde is catalyzed by Lewis acidic Pd(OAc)2, and the nucleophilic oxygen of the resulting hemiacetal reacts with alkyne complexed by Pd(II), giving the alkenyl ethers.

Mass spectral analysis of low-temperature pyrolysis products from poly(tetrahydrofuran)

A poly(tetrahydrofuran) (PTHF) sample of average molecular weight 2000 was subjected to low temperature pyrolysis. The polymer was pyrolyzed in Pyrex tubes (closed at one end) placed at the end of the carrier gas inlet in a gas chromatograph. Pyrolysis was carried out under argon flow in the temperature range 150-350°C. After pyrolysis, the residue in the pyrolysis tube was analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and by direct probe chemical ionization (isobutane CI-MS). Eleven series of oligomeric pyrolyzates were characterized by MALDI-MS and CI-MS. Assignment of chemical structures was aided by tandem mass spectrometry (CI-MS/MS) and by deuteration of hydroxyl end groups in the pyrolyzate. Pyrolysis of poly(tetrahydrofuran) ensues about 175°C in inert atmosphere. The initial pyrolysis products all have at least one hydroxyl end group, which is retained from the low molecular weight starting polymer. The other end group is ‘ethyl ether’, ‘propyl ether’, ‘butyl ether’, or ‘aldehyde’. At higher temperatures (250–350°C) there is an increasing tendency to form products with a combination of ‘alkyl ether’ and/or ‘aldehyde’ end groups. The proportion of products containing the hydroxyl end group diminishes at the higher temperatures. There is little tendency to form ‘alkenyl ether’ end groups during PTHF pyrolysis. Only the ‘butenyl ether’ is observed to any appreciable extent. This is evidently formed mainly via dehydration of oligomers containing a hydroxyl end group. A free radical mechanism is proposed to explain the main degradation products.

Identification and characterization of alkenyl hydrolase (lysoplasmalogenase) in microsomes and identification of a plasmalogen-active phospholipase A 2 in cytosol of small intestinal epithelium

A lysoplasmalogenase (EC 3.3.2.2; EC 3.3.2.5) that liberates free aldehyde from 1-alk-1′-enyl- sn-glycero-3-phospho-ethanolamine or -choline (lysoplasmalogen) was identified and characterized in rat gastrointestinal tract epithelial cells. Glycerophosphoethanolamine was produced in the reaction in equimolar amounts with the free aldehyde. The microsomal membrane associated enzyme was present throughout the length of the small intestines, with the highest activity in the jejunum and proximal ileum. The rate of alkenyl ether bond hydrolysis was dependent on the concentrations of microsomal protein and substrate, and was linear with respect to time. The enzyme hydrolyzed both ethanolamine- and choline-lysoplasmalogens with similar affinities; the K m values were 40 and 66 μM, respectively. The enzyme had no activity with 1-alk-1′-enyl-2-acyl- sn-glycero-3-phospho-ethanolamine or -choline (intact plasmalogen), thus indicating enzyme specificity for a free hydroxyl group at the sn-2 position. The specific activities were 70 nmol/min/mg protein and 57 nmol/min/mg protein, respectively, for ethanolamine- and choline-lysoplasmalogen. The pH optimum was between 6.8 and 7.4. The enzyme required no known cofactors and was not affected by low mM levels of Ca 2+, Mg 2+, EDTA, or EGTA. The detergents, Triton X-100, deoxycholate, and octyl glucoside inhibited the enzyme. The chemical and physical properties of the lysoplasmalogenase were very similar to those of the enzyme in liver and brain microsomes. In developmental studies the specific activities of the small intestinal and liver enzymes increased markedly, 11.1- and 3.4-fold, respectively, in the first ∼40 days of postnatal life. A plasmalogen-active phospholipase A 2 activity was identified in the cytosol of the small intestines (3.3 nmol/min/mg protein) and liver (0.3 nmol/min/mg protein) using a novel coupled enzyme assay with microsomal lysoplasmalogenase as the coupling enzyme.

Stereoselective transformation of 1-alkeny ether (R 1CH=CHOMe) into alkene (R 1CH=CHR 2) based on stereospecific elimination of the vicinal iodo(methoxy)alkane

Treatment of alkenyl methyl ether with ICl rapidly gave 1-chloro-2-iodo-1-methoxyalkane quantitatively. Without isolation, this dihalide was treated with Et 3Al to afford anti-iodo(methoxy)alkane in good yield with high stereoselectivity. The stereochemistry of the starting alkenyl ether did not affect the stereochemical outcome of the product. The use of alkynylaluminum ((RCC) 2AlEt) resulted in alkynylation of the α-chloro-β-iodoether. Anti-iodo(methoxy)alkane was converted into ( Z)-alkene upon treatment with n-BuLi in hexane-ether at −78°C. On the other hand, the reaction of the same anti-iodo(methoxy)alkane with allylsilane-TiCl 4 provided ( E)-alkene.

Lipoproteins are substrates for human secretory group IIA phospholipase A2: preferential hydrolysis of acute phase HDL

Group IIA secretory phospholipase A2 is an acute phase enzyme, co-expressed with serum amyloid A protein. Both are present in atherosclerotic lesions. We report that human normal and acute phase high density lipoproteins and low density lipoprotein are effective substrates for human group IIA phospholipase A2. The enzyme hydrolyzed choline and ethanolamine glycerophospholipids at the sn-2 position resulting in an accumulation of the corresponding lysophospholipids, including the unhydrolyzed alkyl and alkenyl ether derivatives. The hydrolysis of acute phase high density lipoprotein was 2- to 3-fold more rapid and intensive than of normal high density lipoprotein. The hydrolysis of lipoproteins was noted at enzyme concentration as low as 0.05 μg/mg protein, which was within the range observed in the circulation in acute and chronic inflammatory diseases. The enzyme hydrolyzed the different molecular species of the residual glycerophospholipids in proportion to their mass, showing no preference for the release of arachidonic acid. Group IIA phospholipase A2 preferentially attacked the hydroxy and hydroperoxy linoleates and possibly other oxygenated fatty acids, which were released from the glycerophospholipids at early times of incubation. There was no effect on the content or molecular species composition of the sphingomyelins or neutral lipids of the lipoproteins. In conclusion, human plasma lipoproteins are the first reported natural biological substrates for human group IIA phospholipase A2. The enhanced hydrolysis of acute phase high density lipoproteins is probably due to its association with serum amyloid A protein, which enhances the activity of the enzyme and may promote its penetration to the lipid monolayer. As sPLA2-induced hydrolysis of the lipoproteins leads to accumulation of lysophosphatidylcholine and potentially toxic oxygenated fatty acids, overexpression of this enzyme may be proatherogenic. —Pruzanski, W., E. Stefanski, F. C. de Beer, M. C. de Beer, P. Vadas, A. Ravandi, and A. Kuksis. Lipoproteins are substrates for human secretory group IIA phospholipase A2: preferential hydrolysis of acute phase HDL. J. Lipid. Res. 39: 2150–2160.

Synthesis of end‐group functionalized poly(octadecyl vinyl ether)

The cationic polymerization of octadecyl vinyl ether (ODVE) initiated by trimethylsilyl iodide and 1,1-diethoxyethane in the presence of ZnI 2 in toluene at 0°C and 10°C has been investigated. For molecular weights lower than 6000, a linearity of M n with conversion was observed, but for higher molecular weights a strong deviation from calculated values, assuming a living mechanism, was found. Kinetic analysis of the polymerization and the variation of molecular weight as a function of conversion was in agreement with a transfer to monomer with k tr /k p ? 0.006 at 10°C. Analysis of the polymers obtained by termination with methanol provided evidence that the alkenyl ether end-groups formed by the transfer reaction lead to the same acetal end-groups as the active species. As a consequence, it is possible to prepare functionalized polyODVE polymers by end-capping with alcohols. This was confirmed by the synthesis of polyODVE macromonomers by end-capping with 2-hydroxyethyl methacrylate.

Composition of phospholipids of white muscle of six tuna species

A comparative study of the phospholipids of white muscle of six of the commercially utilized tuna species, including quantitative analyses of phospholipid classes and studies of the acyl composition of the major components. Plasmalogen compounds also were identified and quantified. Choline and ethanolamine glycerophospholipids were the most abundant classes in all the samples, as well as the only molecules containing plasmalogens (16:0, 18:0, and 18:1 alkenylether chains). The patterns of fatty acid distribution within each of the phospholipid classes showed general similarities in the species analyzed. However, ratios between certain saturated and polyunsaturated fatty acids in different phospholipid classes showed remarkable differences. The high content of n-3 polyunsaturated fatty acids in the principal phospholipids, such as the plasmalogens, and taking into account the fatty acids possible importance in human nutrition, indicates that the white muscle of tuna species may be a potentially important dietary item.

Asymmetric Hydrogenation of Olefins with Aprotic Oxygen Functionalities Catalyzed by BINAP-Ru(II) Complexes

Cyclic a,b-unsaturated ketones, alkylidene lactones, and alkenyl ethers have been hydrogenated in high enantiomeric excesses by use of BINAP-Ru(I1) complexes (BINAP = 2,2'-bis(dipheny1phosphino)-1,l'-binaphthyl) as catalysts. 2-Alkylidenecyclopentanones were hydrogenated in the presence of [RuCl(BINAP)(benzene)]Cl, Ru2C14(BINAP)2(NEt3), or Ru(OCOCH&(BINAP) in up to 98% ee, while in the case of 2-benzylideneand 2-(3-phenylpropylidene)cyclopentanones, enantiomeric excesses of the hydrogenation were below 50% under the same conditions. The sense of asymmetric induction as well as the enantioselectivity (95% ee) obtained in the hydrogenation of (E)-2-propylidene-y-butyrolactone were the same as those of the (2)-isomer. Lactones, 2and 4-alkylidene-y-butyrolactones, were converted to the corresponding saturated y-butyrolactones in 95% ee. Hydrogenation of diketene with the catalytic system derived from (RuCl[(S)-BINAF'](benzene))Cl and triethylamine or complex Ru~C~~[(S)-BINAPI~(NE~~) established a new synthetic route to (R)-4-methyl-2-oxetanone, a promising monomer of biodegradable polymers, in up to 97% selectivity and 92% ee. Alkenyl ethers, 2-methylenetetrahydrofuran, and 2-methyl-3,4-dihydrofuran have also been hydrogenated to give 2-methyltetrahydrofuran in 91 and 87% ee, respectively.

Preparation of Carbocyclic and Heterocyclic Compounds by the Use of an Allylzinc and an Allylpalladium in Tandem

During the last decade, part of our work was directed at the construction of methylene derivatives of five- and six-membered carbocyclic and heterocyclic compounds (1): methylenecyclopentenes, methylenecyclopentanes, methylenetetrahydrofurans, methylenepyrrolidines and methylenetetrahydropyrans. Our routes start with the addition of 2-(metallomethyl)-2-alkenyl ethers (2) to C≡C, C=X (X = C, O, NR), and epoxides (3) to give 4, which can be derivatized or, more importantly, cyclized to 1 in situ by Pd(0) catalyzed elimination of met-OR2. Special features are the one-pot nature, cleanliness and mildness of most procedures leading to 1. So far, we have found that silyl ether, acetal and ester groups as well as primary C-Cl remain unaffected by zinc reagents 2 (met=ZnBr) under our reaction conditions.1 In initial studies, 3-metallomethyl derivatives of 5-methylenetetrahydropyrans and 5-methylene-N-methylpiperidine were obtained by an intramolecular version of the addition step, a type-II zinc-ene reaction of 2-(bromozincmethyl)-2-propenyl alkenyl ethers and N-methyl-N-{2-(chloromagnesiomethyl)-2-propenyl}allylamine, respectively. An extension of the main theme concerns the preparation of 3,4-dimethylene derivatives of tetrahydropyran and N-methylpiperidine.

A new alkenyl ether giving acetal with stereospecific manner

A new alkenyl ether giving acetal with stereospecific manner

A new alkenyl ether giving acetal with stereospecific manner

A new alkenyl ether, bicyclo[3.3.0]-2-oxa-5-(2-propenyl)-1-octene, can stereospecifically produce cis-fused bicyclo[3.3.0]-2-oxa-(2-pentenyl)-1-alkoxyoctane and the stereochemistry was proved by X-ray analysis.

Hydrolysis of O-Isopropenyl Glucopyranosides Involves C-Protonation and Alkenyl Ether Cleavage and Exhibits a Kinetic Influence of Anomeric Configuration

Hydrolysis of O-Isopropenyl Glucopyranosides Involves C-Protonation and Alkenyl Ether Cleavage and Exhibits a Kinetic Influence of Anomeric Configuration

The lipid composition of selected tissues from a Mediterranean monk seal, Monachus monachus.

The lipid composition of blubber, brain, muscle and heart from a Mediterranean monk seal Monachus monachus (an endangered species) were examined to allow comparisons with more common species of seals. Only neutral lipids (mainly triacylglycerols) were detectable in the blubber lipids, whereas polar lipids predominated in the heart and in the brain. Neutral and polar lipids comprised almost equal proportions in both liver and muscle. Choline glycerophospholipids (CGP) were the major polar lipids, followed by ethanolamine glycerophospholipids (EGP) in the liver, heart and muscle. Cerebrosides accounted for 28.8% of the brain lipids. All lipid classes of the liver contained high levels (31-47%) of polyunsaturated fatty acids (PUFA), with the exception of phosphatidylserine. The total proportion of n-6 PUFA exceeded that of n-3 PUFA in all lipid classes of the liver, due mainly to the high levels of 20:4n-6. The highest level of 20:4n-6 occurred in phosphatidylinositol, where it comprised 32.4% of the total fatty acids. The CGP and EGP of the brain contained lower levels of PUFA than those of the liver, muscle and heart. Alkenyl ethers accounted for 35.8% of the total long-chain moieties in brain EGP. The fatty acid composition of blubber triacylglycerols differed from those of the lipid classes from other tissues in that it had a very low ratio of n-6 to n-3 PUFA (0.3) as a result of a lower content of 20:4n-6.

Isomeric sn‐1‐octadecenyl and sn‐2‐octadecenyl analogues of lysophosphatidylcholine as substrates for acylation and desaturation by plant microsomal membranes

To provide supporting and independent evidence for lipid-linked desaturation of acyl groups in plant microsomal membranes, ether-analogous substrates were synthesized and used for in-vitro desaturation studies. The substrates included 1-O-(9-cis-octadecenyl)-sn-glycero-3-phosphocholine and 2-O-(9-cis-octadecenyl)-sn-glycero-3-phosphocholine as well as labelled 1-O-(9-cis-[9,10-3H2]octadecenyl)-sn-glycero-3-phosphocholine. In experiments with microsomal membranes from developing fruits of sunflower, it was shown that both isomeric alkenyl ether phospholipids were acylated with [14C]oleoyl-CoA and [14C]palmitoyl-CoA. In the presence of O2 and NADH, the oleoyl groups incorporated into both compounds, i.e. at the sn-1 and sn-2 positions of the glycerol backbone of the substrate, were desaturated to linoleoyl residues in similar proportions. Under the same conditions, an additional double bond, but not an enol-ether double bond, was introduced into the ether-linked side chain of acylated 1-O-(9-cis-[9,10-3H2]octadecenyl)-sn-glycero-3-phosphocholine. This represents the first demonstration of this type of desaturation with an alkenyl ether phospholipid and confirms previous conclusions that plants introduce second and further double bonds into lipid-linked acyl groups.

Fragmentation of 1- and 3-metroxypropene ions another part of the C 4H 8O + [rad] potential energy surface

The fragmentation mechanisms of metastable ionized 1- and 3-methoxypropene have been examined in detail by using ionization and appearance energy measurements metastable ion and collisional activation mass spectra, and a variety of isotopically labeled molecules. These metastable C 4H 8O + ions fragment by loss of H , CH 3, and H 2CO, and the experimental observations allowed the construction of the potential energy diagram which describes their interconversion and the participation of four other distonic and carbene C 4H 8O + ions. It was found that these two methyl alkenyl ether ions had no common reaction channel with either the 2-methoxy isomer or with any of the alcohol, keto, or enol C 4H 8O + isomers which previously have been extensively studied.

ChemInform Abstract: An Efficient Synthesis of Alkenyl and Alkynyl Silyl Ethers.

Abstract A general synthesis of alkynyl and alkenyl silylethers is described. This involves reaction of alkynyl or alkenyl organometallic reagents, usually the lithio derivatives, with chlorodimethylaminodimethylsilane, followed by reaction of the product with an alcohol.

Phospholipid analysis of human eosinophils: high levels of alkylacylglycerophosphocholine (PAF precursor).

The phospholipid composition and fatty acid profiles of human eosinophils were studied. Extremely high levels of ether phospholipids were found in this type of cell, such as alkylacylglycerophosphocholine (GPC) and alkenylacylglycerophosphoethanolamine (GPE); these two ether phospholipids accounted for about three-fourths of the choline and ethanolamine glycerophospholipids (CGP and EGP), respectively. Fatty acid analyses revealed that very large portions of arachidonic acid (20:4) were esterified to alkylacyl-GPC (92.0% in CGP) and alkenylacyl-GPE (86.6% in EGP), respectively. While high amounts of alkylacyl-GPC and the abundance of 20:4 in this ether phospholipid have been observed in other types of blood cells of various animals, these percentages for human eosinophils are the highest among such cells. These results suggest that alkyl and alkenyl ether phospholipids play essential roles in human eosinophils in various physiological and pathological conditions.

A simplified approach to the analysis of subclasses of phospholipids: application to human platelets.

A procedure for the determination of the proportions of diacyl, alkenylacyl and alkylacyl subclasses of glycerophospholipids was developed. The procedure involves: (1) acid methanolysis of the phospholipid followed by Bligh/Dyer extraction of fatty acid methyl esters (FAME) derived from acyl chain types, dimethylacetals (DMA) derived from alkenyl ether chain types, and lysoalkyl phosphatidic acids (lysoalkyl-PA) derived from alkyl ether chain types; and (2) subsequent acetolysis to convert the lysoalkyl-PA to monoalkyl glycerol diacetates (MAGD). GLC analysis and quantitation (using internal standard, 21:0 FAME) of FAME, DMA and MAGD allowed calculation of the proportions of the three molecular subclasses. The methanolysis/acetolysis procedure gave an overall mean phospholipid recovery of 95 +/- 3%. Analysis of the major phospholipids in four separate preparations of fresh resting human platelets by this procedure showed the following range of molecular subclasses: phosphatidylcholine (PC), 86-92 mol % diacyl, 6-10 mol % alkylacyl and 2-3 mol % alkenylacyl; and phosphatidylethanoline (PE), 39-60 mol % diacyl, 5-8 mol % alkylacyl and 34-55 mol % alkenylacyl. The results of these subclass analyses were in general agreement with those reported in the literature.

Oxidation of 1-O-(alk-1-enyl)-2,3-di-O-acylglycerols: models for plasmalogen oxidation.

Alk-1-enyl diacyl glycerides, model compounds for plasmalogen lipids, were synthesized for use as substrates in oxidation studies. The neutral plasmalogen glycerides prepared included 1-O-(hexadec-1-enyl)-2,3-di-O-stearoylglycerol (4a) and 1-O-(hexadec-1-enyl)-2-O-linoleoyl-3-O-stearoylglycerol (4b). Oxidative disappearance of these glycerides was followed directly by high performance liquid chromatography (HPLC). The extent of oxidation of the side chains of these glycerides, i.e. the alkenyl ether and fatty acyl functions, was monitored by conversion of the side chains to dimethylacetal and methyl ester by methanolysis, followed by subsequent gas chromatography (GC) of the methanolysis products. Both analytical approaches show that the alkenyl ether function of neat 4a oxidizes more slowly than neat ethyl linoleate. However, the rate of alkenyl ether loss from 4a is accelerated in the presence of added ethyl linoleate. Moreover, when the linoleoyl group is incorporated into the 2-position of the alkenyl glyceride, as in 4b, the rate of loss of the alkenyl group was shown to be similar to the rate of loss of the linoleoyl group. These results suggest that oxidation of plasmalogen glycerides should not be ignored as a factor that contributes to the oxidative instability of animal tissue.