Choline long-chained esters

Figure 15.20. Soft quaterneiry ammonium antimicrobials designed as long-chain ester of choline, betaine, or L-carnitine.

Phospholipids are also found which have similar structures (Table 12.6). These include lysophospholipids, which have only one of the two possible positions of glycerol esterified, almost invariably at carbon 1, and the plas-malogens, in which there is a long chain vinyl ether at carbon 1 instead of a fatty acid ester. These compounds also contain an amino alcohol, which may be either serine, ethanolamine or choline. Other rarer phospholipids are the monoacyl monoether, the diether and the phosphono forms. 

Figure 12.12 Sphingomyelins. Sphingomyelins are esters of a ceramide and phospho-ryl choline. However, similar compounds are ceramide-1-phosphoryl ethanolamines and phosphono forms of sphingolipids. Ceramides W-acyl-sphingosines) are amides of a long chain di- or trihydroxy base containing 12 to 22 carbon atoms, of which sphingosine (4-sphingenine) is the commonest, and a long chain fatty acid whose acyl chain is shown by R1. This may contain up to 26 carbon atoms.

Structural formula A is typical of a group of compounds commonly called phosphoglycerides. In this particular depiction the symbols R1 and R2 are long-chain carboxylic acids linked in an ester linkage to the primary and secondary alcohol residues of glycerol. The symbol X is a mixed venue with a wide variety of bases—for example, choline (HOCH2CH2 N (CH3)3) or... 

In nature, the more common amphiphiles are phospholipids. These are derivatives of glycerol (1,2,3-trihydroxypropane), in which two alcohols form esters with long chain carboxylic acids. The third alcohol forms a phosphate ester, and the phosphate then makes another ester with a simpler alcohol. This creates structures such as phosphatidyl choline, phosphatidyl serine, and phosphatidyl ethanolamine (see next page). The polar group can... 

Because these molecules carry two long hydrophobic fatty acid chains and a polar head group (the phosphate and choline substituent), they are capable of forming micelles in aqueous solution (see Real Life 19-1). In the micelles, the phosphate unit is solubilized by water, and the ester chains are clustered inside the hydrophobic micellar sphere (Figure 20-2A). 

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