Fatty acid acyl ester

Hydroxylaminolysis, treatment with stronger alkali (0.5 m NaOH, 2 h, 100°C) and alkaline methanolysis (0.25 m NaOMe, 1 h, 50°C) lead to complete O-deacylation of LPS and lipid A (176). Particularly in the case of alkaline methanolysis, ester-linked 3-acyloxyacyl residues undergo, in addition to transmethylation, a -elimination reaction, whereby the (R)-3-hy-droxy fatty acid ester is first transformed into the a,/ -unsaturated and then into the (S.-R -methoxy fatty acid methyl ester. The acyl substituent, on the other hand, is eliminated in the form of the free fatty acid (176). In fact, the presence of a 3-methoxyacyl derivative in the fatty acid spectrum of a given LPS is a strong indication for the presence of an ester-bound 3-acyloxyacyl... 

A simple approach for lipidation of peptides with di-fatty acid substituted glycerol moieties is based on the use of glyceric acid.119" For this purpose (2i )-glyceric acid is esterified at the two hydroxy groups with fatty acid acyl chlorides and the resulting lipophilic synthon (18) is used directly as an active ester, e.g. Pfp ester, to acylate selected amino groups of peptides, or is used to acylate suitably functionalized spacers. 

Therefore, of the 2 moles of ester-bound 3-OH-14 0 one is 3-0-acylated by tetradecanoic acid the other should carry a free 3-hydroxyl group. This latter assumption was proven to be correct by the following experiment. Lipid A was treated with t-butyldimethylsilylchloride, ester-bound fatty acids were trans-esterified by NaOCH3 and analysed by gas-liquid chromatography. Besides the other expected fatty acid methyl esters (12 0, 16 0, 3-OCH3-14 0) approximately 1 mole (per 2 moles glucosamine) of the t-butyldimethylsilylether of 3-hydroxytetradecanoic acid me-thylester could be identified (26). 

The method can be applied for saturated fatty acids, unsaturated fatty acids, fatty esters, fatty alcohols and acyl-glycerols. The regression is based on 1200 data points. The absolute deviation in predicting vapor pressure is 6.82%. Another advantage of Eq. (14.1) is the capability of predicting the VLE of mixtures of fatty acids and esters by using the UNIFAC model for liquid activity. The comparison with experimental data shows good accuracy not achieved by other methods [40]. 

Fatty acid biosynthesis. Activated as its coenzyme A thioester, the growing fatty acid (acyl-CoA) acylates malonyl-CoA in a malonic ester synthesis. Two carbon atoms are added, with the third lost as C02. Enzymatic reduction, dehydration, and further reduction gives a fatty acid that has been lengthened by two carbon atoms. 

Bomscheuer, U.T., and T. Yamane, Fatty Acid Vinyl Esters as Acylating Agents A New Method for the Enzymatic Synthesis of Monoacylglycerols, J. Am. Oil Chem. Soc. 72 193-197 (1995). 

The mechanism by which xenobiotic alcohols or esters are converted to fatty acid esters has not been studied. They could be formed by the action of lyase enzymes in the presence of fatty acid glyceryl esters, as in the conversion of farnesol to farnesol fatty acid esters (150). Some lipolytic acyl hydrolase enzymes from plants readily catalyze the transfer of lipid-bound fatty acids to low MW alcohol acceptors (150.151) and enzymes of this class could be responsible for the occasional formation of fatty acid conjugates of xenobiotic alcohols. Mechanisms involving fatty acid acyl CoA, phospholipids, or direct esterification with fatty acids might also be involved (1 ). 

Fig. 7. Current understanding of the synthesis and degradation of fatty acid ethyl esters. FA, fatty acid FA-CoA, fatty acyl-CoA FAEE, fatty acid ethyl esters AEAT, acyl-CoA ethanol acyltransferase.

Diczfalusy MA, Bjorkhem I, Einarsson C. Alexson SEH. Formation of fatty acid ethyl esters in rat Uver microsomes. Evidence for a key role for acyl-CoA ethanol O-acyltransferase. Eur J Biochem 1999 259 404-411. 

Figure 2. GC-MS total ion chromatogram of the total lipid extract of a potsherd recovered from the fill of a medieval ditch. Peak identities I4-T8, 20 and 25 are saturated fatty acids (as TMS ester derivatives) containing 14-18, 20 and 25 acyl carbon atoms respectively 16 1,18 1 and 20 1 are mono-unsaturated fatty acids (TMS esters) containing 16,18 and 20 acyl carbon atoms, respectively D32, D34 and D36 are diacylglycerols (TMS ethers) containing 32, 34 and 36 acyl carbon atoms, respectively 44, 46, 48, 50, 52 and 54 are triacylglycerols containing 44, 46, 48, 50, 52 and 54 acyl carbon atoms, respectively 1 is nonacosane, 2 is nonacosan-15-one, and 3 is nonacosan-lS-ol (TMS ether). Analyses were performed using a I2m x 0.22 mm i.d. BP-1 coated (immobilized dimethyl polysiloxane, 0.1 flm film thickness) fused-silica capillary. After on-column injection and a 2-minute delay the GC oven temperature was programmed from 50 to 350 °C at 10°C/min. (Reproduced from reference 1183] with permission).

Figure 7.19 Two-step synthesis of fatty acid glucamides by reductive alkylation of methylamine with glucose using Raney nickel as the hydrogenation catalyst to obtain Al-methyl glucamine, which is acylated by a base-catalyzed reaction with fatty acid methyl ester in a second step.

The lipid acyl hydrolase from potato tubers (described above) will transfer fatty acids from a donor lipid to a suitable alcohol acceptor. This effect is illustrated in Fig. 3 which shows the results obtained on adding increasing amounts of methanol to a system containing a lipid substrate and the enzyme at 30% methanol, the major reaction product is fatty acid methyl ester, and a relatively small amount of free fatty acid is produced. The affinity of the enzyme for methanol is approximately 10 times that for water, hence the acyltransferase activity is greater than the acyl hydrolase activity. 

Hg.3. Effect of methanol concentration on acyltransferase activity of lipolytic acyl hydrolase. Amounts of free fatty acids (circles) and fatty acid methyl esters formed (triangles) or lyso-phosphatidylcholine deacylated (squares) in 10-min incubations at 2S°C are given as percentage of substrate (lysophosphatidylcholine) added. (Reproduced from Galliard and Dennis, 1974, by permission.)... 

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