Plasmalogens neutral

Similar to aUcyl forms, the mono- and dialk-l-enyl ethers of glycerol have been identified in natural samples, whereas no trialk-l-enyl ethers have been isolated so far. Acylated (mono- and diacyl derivatives) alk-l-enyl ethers (or neutral plasmalogens) have been also reported (2). 

Ether analogs of triacylglycerols have been described. l-Alkyl-2,3-diacyl-sn-glycerols are characteristically elevated in tumor lipids and l-alk-l -enyl-2,3-diacyl-sn-glycerols (neutral plasmalogens) have also been detected in tumors, in adipose tissue of mammals, and in fish liver oil. Alkylacetylacylglycerols, RAF precursors, also have been described in human leukemic cells. 

Fig. 132. Analysis of the eluate fractions of a column-chromatographic separation of Hydrolagus colliei liver oil. I neutral plasmalogens II alkyl diglycerides III triglycerides (cf with Fig.. 131, No. 2)...

This has enabled neutral plasmalogens to be detected in the presence of free aldehydes [183] combined and free aldehydes to be separated [183] and aldehydes, dimethylacetals and methyl esters to be fractionated and isolated [185] (see procedures, p. 373). Neutral plasmalogens can be detected by means of the SRS-technique (p. 88) after chromatographing in the first direction, the alkenyl ethers are hydrolysed on the layer with hydrogen chloride vapour the aldehydes and the diglycerides formed are then separated by chromatography in the second direction [183]. Fig. 134 illustrates the detection of neutral plasmalogens in a shark liver oil by means of TLC. 

Fig. 134. Detection of neutral plasmalogens in the liver oil of a shark ( Ratfish , Hydrolagus colliei) [183]. Adsorbent silica gel G solvent 1 direction petrol ether (40—60° C)-diethyl ether (95 + 5). After development in the first direction the plate was exposed 5 min to HCl vapour solvent 2 direction petrol ether (40—60° C)-diethyl ether (80 + 20) times of run 40 min in both cases visualisation carbonisation by heating with chromic acid/sulphuric acid amounts 300 (jtg liver oil plus 15 [ig palmitaldehyde. 1 palmitaldehyde 2 aldehydes from neutral plasmalogens ...

Fig. 136. Isolation of neutral plasmalogens and alkyl diglycerides from the human perinephrium [181]. Adsorbent silica gel G solvent hexane-diethyl ether (99 + 5), double development times of run 40 min each visualisation carbonisation by heating with chromic acid/sulphuric acid, a lipid extract 6 first concentration stage c second concentration stage d third concentration stage e neutral plasmalogens / alkyl diglycerides...

Neutral plasmalogens are related compounds in which position 1 of L-glycerol is linked by a vinyl ether bond (the double bond is of the c s-configuration) to an alkyl moiety. They have been detected in small amounts only in a few animal tissues. Although the vinyl ether linkage is stable to basic hydrolysis conditions, it is disrupted by acid (and by mercury salts) with the formation of a long-chain aldehyde, i.e. 

Once an alkoxy derivahve of dihydroxyacetone is formed, reduchon fo fhe 2-OH form, further acylation, and conversion to various alkyl phospholipids and neutral lipids can occur. The pathways (Eq. 21-12, steps b-f) are closely akin to those of Fig. 21-4. The conversion of alkoxy lipids fo plasmalogens occurs by oxidative desaturation (Eq. 21-12, step/). ° The initial steps in the S5mthesis of efher-linked lipids take place principally in the peroxisomes. Enzymes catalyzing both the acylation of dihydroxyacetone phosphate and the S5mthesis of alkyl-dihydroxyacetone-P (step a, Eq. 

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