Phenolic ether lipids

An alternative cleanup procedure is the partition of the raw extract, which often contains considerable amounts of lipid material, between an organic and an aqueous sodium hydroxide phase. With this partitioning scheme, the analytes are further fractionated into estrogens and nonestrogens. The presence of phenolic groups in the molecules of estrogens such as diethylstilbestrol and zeranol ensures their complete extraction from organic phases such as chloroform or tert.-butyl methyl ether into the aqueous sodium hydroxide phase (435, 438, 447). Further purification could be accomplished by neutralization of the sodium hydroxide solution and back-extraction of the contained diethylstilbestrol into diethyl ether (435), or adjustment of the pH of the sodium hydroxide solution to 10.6-10.8 and back-extraction of the contained zeranol into a chloroform phase (447). 

A palladium-based method has been developed for the alkylation of the phenolic oxygen of tyrosine residues. Fig. 5f (61). In this reaction, allylic carbonates, esters, and carbamates are activated by palladium(O) complexes in aqueous solution to form electrophilic pi-allyl complexes. These species react at pH 8-10 with the phenolate anions of tyrosine residues, which results in the formation of an aryl ether and the regeneration of the Pd(0) catalyst. The reaction requires P(m-C6H4S03 )3 as a water-soluble phosphine ligand. Activated pi-allyl complexes that do not react with tyrosine residues undergo P-hydride elimination under the basic conditions to yield diene by-products. A particularly attractive feature of this method is its ability to use substrates with charged groups in the allylic positions. This ability allows hydrophobic substrates, such as lipids, to be solubilized to facilitate protein modification. 

Phenolic compounds are generally extracted using various mixtures of water and alcohol. Anthocyanins are traditionally extracted in the flavylium cation form, with methanol-containing hydrochloric acid. For the acylated anthocyanins, it is necessary to replace the hydrochloric acid with a weaker acid, either formic or acetic acid. Lipids, carotenoids, and chlorophyll are removed from the water-alcohol extracts with hexane, chloroform, or petroleum ether. The defatted extracts may be analyzed directly or after a partitioning of the phenolics into ethyl acetate. 

With 3,5-dimethoxybenzoyl chloride used in the monoacylation of cyclohexanone to produce finally the same (MeO ArC synthon, an alternative synthesis of cardol 8(Z)-monene was developed [138]. Fig( 4)-49, Persoonol dimethyl ether (5-[(Z)-undec-3-enyl]resorcinol dimethyl ether) was synthesised from 3,5-dimethoxybenzyl alcohol [149], This same reactant has been employed for a range of 5-substituted resorcinols although its application to unsaturated phenolic lipids was not discussed [228]. Acetylenic methods have proved valuable for deriving phenolic lipidic double bonds in the Z-configurations and with advances in boration methodology [229] the corresponding E-isomers are accessible. 

In earlier syntheses of the methyl ethers of (15 1)-cardanol (ref. 136) and urushiol (ref. 137) it is doubtful if the products were stereochemically pure. Nonetheless this work represents the first progress towards obtaining unsaturated methyl ethers of the phenolic lipids. Early difficulties centred on the lack of specificity in the reduction of the triple bond, in the removal of the protective group on the phenolic OH without affecting the double bond and, before kinetic and thermodynamic control was used, on lack of steric control in the Wittig reaction. 

The method was extended to novolak and resol cardanol/formaldehyde copolymers. HO-protected phenolic lipids have also been reacted. Thus, cardanol methyl ether and esters have been hydrosilated with HSiClj and then reacted with methanol to afford methoxysilyl products useful as coupling agents for phenolic resins in sand cores (ref. 256). 

From Richards et al. (2002). Emulsions contained 5% lipid, 1 % emulsifier (Brij 700 = polyoxyethylene fatty ether) and 10 mM acetate-imidazole buffer at pH 3.0. Partitioning by centrifugation was followed by analysing the continuous phase for emulsifier by density measurements and for antioxidants by total phenolic concentrations. Oxidations of emulsions were carried out at 32°C. 

In many studies on plasma cobalamin forms, the method initially described by Lindstrand and Stahlberg in 1963 (10) is still being used. One volume of plasma is poured into four volumes of absolute alcohol and heated for 20 min at 80 C. After removal of precipitate by filtration the alcohol in the filtrate is evaporated under vacuum at 30°C. The residual water phase is extracted three to six times with ether to remove lipid material. In the next step cobalamins are extracted from the water phase into phenol by shaking in four volumes of phenol with 15% water. The phenol phase is shaken with one part of acetone, three parts of ether, and a small amount of water. Phenol in the resulting water phase is further removed with ether. The water phase containing the cobalamin is evaporated to remove residual ether. Linnell et al. (65,66) used essentially the same procedure with smaller volumes of blood plasma. 

Ratnayake, W. M. N. Timmins, A. Ohshima, T. Ackman, R. G. Mass spectra of fatty acid derivatives, of isopropylidenes of novel glyceryl ethers of cod muscle and of phenolic acetates obtained with the Finnigan MAT ion trap detector. Lipids. 1986, 27, 518-524. 

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