Ether phospholipids oxidized

The hydroperoxides obtained on thermal oxidation of cholesteryl acetate (191e) can be selectively separated by SPE and elution with a polar solvent. After reduction to the corresponding alcohols by NaBH4 and further derivatization to the trimethylsilyl ether, the products can be subjected to GLC with ion-trap MS detection. It can be thus demonstrated with the aid of standards that under the oxidation conditions (160 °C for 90 min) only the 7-position is attacked, leading to the la- and 7/3-hydroperoxy derivatives, while the plausible 4-position remains unscathed . Treatment of erythrocite ghosts with t-BuOOH causes a manyfold content increase of 5-hydroxyeicosatetraenoic acid (5-HETE), 5-hydroperoxyeicosatetraenoic acid (5-HPETE) and 5-oxoeicosatetraenoic acid (5-oxo-ETE) residues of phospholipids. These acids can be separated by HPLC, identified and quantitized by tandem MS . ... 

Plasmalogens are monoacyl monoalk-l-enyl ether forms of phospholipids. The most common forms of plasmalogens are the choline, ethanolamine, and serine derivatives. They are present in most animal tissues, especially in the mammalian brain. Plasmalogens are stmctural components of membranes. It has been proposed that plasmalogens protect membranes against oxidative stress (9). 

A procedure for the release of the diacylglycerol moieties from galactosyidiacylglycerols (including sulfoquinovosyidiacylglycerols) has been described, involving periodic acid oxidation in methanol followed by incubation with 1,1-dimethylhydrazine [382]. The diacylglycerols are then converted to UV-absorbing derivatives for separation by means of HPLC [475], but equally it should be possible to prepare TMS or BDMS ethers and use the GC conditions developed for the analysis of the equivalent compounds released from phospholipids (see Section C above). 

The polymer-surfactant complex has high surfeice viscosity and elasticity (i.e. surfeice viscoelasticity), both will enhance the foam stability (see below). The amphoteric surfactants such as betaines and the phospholipid surfeictants when used in conjunction with alkyl sulfeites or alkyl ether sulfeites can also enhance the foam stability. All these molecules strengthen the film of surfactant at the air/water interface, thus modifying the lather from a loose lacy structure to a rich, dense, small bubble size, luxurious foam. Several foam boosters have been suggested and these include fatty acid alkanolamide, amine oxides. Fatty alcohol and fatty acids can also act as foam boosters when used at levels of 0.25-0.5 %. Several approaches have been considered to explain foam stability (a) Surface viscosity and elasticity theory The adsorbed surfeictant film is assumed to control the mechanical-dynamical properties of the surface layers by virtue of its surface viscosity and elasticity. This may be true for thick films (> 100 nm) whereby intermolecular forces are less dominant. Some correlations... 

PE is another major phospholipid in the membranes of eukaryotic cells. PE plasmalogens, which comprise —50% of total PE lipids, contain a vinyl ether-linked hydrocarbon chain in the sn-l position instead of an ester-linked chain. Plasmalogens represent a major source of arachidonic acid, an important second messenger, and are also thought to have an important protective role against oxidative damage [48]. 

The Hoveyda group worked out an elegant cross metathesis of terminal alkenes with vinyl ethers or allylic amides [63]. Functionalized vinyl ethers and allylic amides can be directly accessed with unprecedented Z-selectivity, which have been applied to the total synthesis of two highly valuable natural products including an anti-oxidant plasmalogen phospholipid (Fig. 29) and a potent immunostimulant KRN7000. 

Another type of lipid, the ether-linked phospholipids (e.g., plasmalogens), comprises about 20% of membrane phospholipids (Figure 7). Plasmalogen synthesis requires enzymes present in both peroxisomes and the endoplasmic reticulum. These lipids are thought to be part of the cellular defense mechanism against oxidative injury. 

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