Alkyl-diacyl-glycerol

Cyclic carbohydrates with two alkyl chains (e.g. 1,2-dialkyl (or 1,2-diacyl) glycerol 8 a (sug=Glcp, Galp) present structural similarities with glycerophospho-lipids. They form complex mesophases such as bicontinuous cubic phases, inverted hexagonal phases or myelin figures [58-61]. Other dialkyl derivatives... 

The new lipase substrates are enantiomerically pure O-alkyl-diacyl-sn-glycerols (Figure 1). Pyrene as a fluorophore is linked to the omega end of the fatty acid in the sn-2 position of glycerol. In the sn-1 or sn- i position, the lipids contain a trinitrophenylamino-substituted fatty acyl chain as a fluorescence quencher. The third substituent is a hexadecyl residue connected to the glycerol backbone by an ether linkage to stabilize this position towards hydrolysis. 

Figure 2. Phospholipid subclasses. Phospholipid subciasses are categorized by the type of covalent attachment of aliphatic constituents to the sr>l carbon of the glycerol backbone. The aliphatic chain of diacyl, plasmalogen, and alkyl-ether subclasses of phospholipids contain an ester, vinyl-ether, or alkyl-ether bond at the sn-l position, respectively.

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. 

The term glycophosphatidylinosiiol is used to designate glycolipids which contain saccharides glycosidically linked to the inositol moiety of phosphatidylinositols (e.g., diacyl-sn-glycero-3-phosphoinositol), inclusive of lyso- (Lip-2.6 in ref. 1) species and those with various Oacyl-, 0-alkyl-, 0-alk-1-en-l-yl- (e.g., plasmanylinositols 1), or other substitutions on their glycerol or inositol residues. 

The choline- and ethanolamine-containing phospholipids of human platelets can be subdivided, based on the nature of the linkage to the fatty acid residue at the sn-1 position of the glycerol backbone, into 1,2-diacyl, l-O-alkyl-2-acyl and l-0-alk-l -enyl-2-acyl species (Table 1.2). The majority of arachidonic acid in the phosphatidylcholines is present in the diacyl species while 1-0-alk-l enyl-2-acyl-PE (plasmalogen) contains most of the arachidonic acid in the phosphatidylethanolamines. The amount of arachidonic acid present in the diacyl species of phosphatidylethanolamine is similar to that in diacyl phosphatidylcholine. Ferret et al have shown that the distribution of arachidonate in the phospholipids of the platelet plasma membrane is asymmetric, the majority of it being present in the inner leaflet. 

Jost, U. 1974. 1-alkyl-2,3-diacyl-sn-glycerol, the major lipid in the Harderian gland of rabbits. Hopper-Seyler s.Z. Physiol. Chem., 355, 422-426. 

Fig. 5 a, b. Incorporation of homologous saturated l-0-[l- C]alkylglycerols from an equimolar mixture into (a) l-O-aIkyl-2-acyl-sn-glycerols and (b) l-0-alkyl-2,3-diacyl-sn-glycerols of photomixotrophic cell suspension cultures of B. napus. (The dotted line represents the percentage composition of each substrate in the equimolar mixture.) From Weber and Mangold [62]... 

In the high mass accuracy/resolution mass spectrometry-based shotgun lipidomics approach, the overlaps between SM and M-f1 C isotopologue of PC species, and between PC subclasses can be resolved [35]. Moreover, the linkages of alkyl vs. alkenyl at the sn-1 position of glycerol and the fatty acyl chains of diacyl species are also identified by product-ion analysis [35,36]. Clearly, this approach provides much more structural information than that of the tandem MS approach as aforementioned. 

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