Fatty acylated, selectively synthesis

Synthesis of a Fatty Acylated, Selectively Deprotected Disaccha-ride... 

The next step in phospholipid biosynthesis is catalyzed by 1-acylglycerol phosphate acyltransferase (the plsC gene product) which acylates the product of the PlsB step to form phosphatidic acid (Fig. 5). Phosphatidic acid comprises only about 0.1% of the total phospholipid in E. coli and turns over rapidly, a property consistent with its role as an intermediate in phospholipid synthesis. The 1-acylglycerol phosphate acyltransferase is thought to transfer unsaturated fatty acids selectively to the 2-position. The plsC gene is universally expressed in bacteria. 

After consumption of usual food fats, the major products of digestion that are absorbed are 2 in-MG and FFA. In the small intestinal cells, the sn-2-MG react with activated FFA to be converted by a multienzyme complex into TG. The excess FFA react with sn-3-glycerophosphate to form lysophospha-tidic acids, which are further converted into phosphatidic acids. Dephosphorylation results in ot-1, 2-DG, which are precursors of both TG and PL. What happens after the influx of sn-l,3-DG or sn-l(3)-MG into the intestinal cell is less clear. A series of competing reactions must be considered, such as complete digestion, acylation, transacylation, phosphorylation, and intact excretion out of the intestinal cells as well. Lipases are present in the intestinal cells but their action seems to be reduced by other intestinal cell constituents (28). The sn-1,2-DG seem to be poor substrates for intestinal TG synthesis (29), whereas in-l-MG can be phosphorylated into lysophosphatidic acid (30) and possibly be metabolized fur-dier as described above. It has to be realized, however, that j -3-glycerophosphate acyltransferase possesses fatty acid selectively, incorporating mainly palmitic acid at the sn-1... 

As well as being the substrate for fatty acid synthesis, malonyl CoA has an important role in controlling (3-oxidation of fatty acids. Malonyl CoA is a potent inhibitor of carnitine palmitoyl transferase 1, the mitochondrial outer membrane enzyme that regulates uptake of fatty acyl CoA into the mitochondria (section 5.5.1). This means that, under conditions in which fatty acids are being synthesized in the cytosol, there will not be uptake into the mitochondria for (3-oxidation. (See also section 10.6.2.1 for a discussion of the role of malonyl CoA in regulating muscle fuel selection.)... 

Early work on aryloxyphenoxypropionates failed to show any metabolic effects except those on acyl lipid synthesis. The general inhibition of labeling of all acyl lipid classes but not that of sterols or terpenoids led to the idea that de novo fatty acid synthesis was being reduced. In fact, there is little effect on fatty acid elongation (e.g.. Table 3.13). Of the two enzyme systems involved in de novo synthesis, it has now been established that the aryloxyphenoxypropionates and cyclohexanediones only affect acetyl-CoA carboxylase. Moreover, this carboxylase from dicotyledons (resistant) appears to be different from that in monocotyledons (sensitive) because the selectivity of herbicides (including stereospecificity) is retained during in vitro measurements (Table 3.14). 

Among the aldonolactone-based surfactants are aldonolactone-linked fatty esters which have been prepared by selective acylation of unprotected aldono-1,4-lac-tones or aldono-1,5-lactones, One of the first reported examples of this type of surfactant was applied to the enzymatic synthesis of 6-0-aUcanoylgluconolactones [35], Thus, 6-0-decanoyl- and 6-0-dodecanoyl- derivatives (21a and 21b, respectively, Scheme 8) were obtained in 26-27% yield by esterification of glucono-1,5-lactone (1) at C-6 with the corresponding 2,2,2-trichloroethyl carboxylate in the presence of porcine pancreatic lipase (PPL) as catalyst. Compounds 21a,b are soluble in water at 90-96°C but precipitate when cooled to 30-37°C, NMR and GC-MS analysis after dissolution and precipitation indicated the presence in the mixture of compound 21b, the glucono-1,4-lactone-derived ester 22, and the... 

The synthesis of long-chain fatty acid esters of carbohydrates is inherently more demanding. It was found that glucose did not react with vinyl laurate in a pure ionic liquid medium, but in biphasic tert-butyl alcohol/[BMIm][PF6], glucose could be acylated by the vinyl esters of O, 2-Cu, fatty acids. The best results were obtained with CaLB, which was twice as active as TIL, and the selectivity for acylation at C-6 was high [114]. The esterification of glucose with palmitic acid, which is, in an industrial context, to be preferred over transesterification, has recently been demonstrated in tert-butyl alcohol/[BMIm][PF6] medium [115]. 

Once bearing some substituents, the decrease of polarity of the sucrose derivatives makes them soluble in less-polar solvents, such as acetone or tert-butanol, in which some lipases are able to catalyze esterifications. Unlike proteases, which necessitate most often the use of an activated acyl donor (such as vinyl or trifluoroethyl esters), lipases are active with simple esters and even the parent carboxylic acids in the presence of a water scavenger. The selectivity of the lipase-catalyzed second esterification is specific for OH-6 allowing the synthesis of mixed T,6 -diesters.123,124 For some lipases, a chain-length dependence on the regiochemistry was observed.125 Selectively substituted monoesters were thus prepared and studied for their solution and thermotropic behavior.126,127 Combinations of enzyme-mediated and purely chemical esterifications led to a series of specifically substituted sucrose fatty acid diesters with variations in the chain length, the level of saturation, and the position on the sugar backbone. This allowed the impact of structural variations on thermotropic properties to be demonstrated (compare Section III.l).128... 

R, Olsen, J.G., McGuire, K.A., and Henriksen, A., Fatty acid synthesis. Role of active site histidines and lysine in Cys-His-His-type beta-ketoacyl-acyl carrier protein synthases, FEBS J. 273, 695-710, 2(X)6 Ryn, Y, Kim, KJ., Rosennser, C.A., and Scott, A., Decarboxylative Qaisen condensation catalyzed by in vitro selected ribozymes, Chem. Commun. 7, 1439-1441, 2006. 

Synthesis of a structured TAG with PUFA confined to either the l-(3-) or 2-position requires 1,3-selective lipases to interesterify a TAG using FFA or fatty acid esters (reaction 1), or to transesterify two different populations of TAG molecules (Fig. 3). Alternatively, a two-step approach can be employed, where a TAG is first subjected to 1,3-selective lipolysis, resulting in 2-MAG that is carefully isolated, then crystallized, to prevent acyl migration. The second step is 1,3-selective esterification of the 2-MAG.f " Such an approach results in a 72-85% yield and >95%... 

In the plastids, acyltransferases provide a direct route for entrance of acyl groups from ACP to membrane lipids. Since this is the standard pathway for phosphatidic acid synthesis in E. coli and cyanobacteria, both the enzymes of phosphatidic acid synthesis in plastids and the glycerolipid backbones they produce are termed prokaryotic . In both chloroplasts and non-green plastids, the glycerol-3-phosphate acyltransferase is a soluble enzyme that, unlike the E. coli enzyme, shows preference for 18 1-ACP over 16 0-ACP. The lysophosphatidic acid acyltransferase, which is a component of the inner envelope of plastids, is extremely selective for 16 0-ACP. The presence of a 16-carbon fatty acid at the... 

Lipase-catalysed interesterification has found many applications in production of edible and specialty lipids due to mild reaction conditions, high catalytic efficiency, the inherent selectivity of natural catalysts and production of much purer products as compared to chemical methods (Sonnet, 1988). Lipases (hydrolases) are used for hydrolysis and ester synthesis. They are classified as non-specific or random, positional specific or 1,3-specific and acyl group- or structure-specific, depending on their activity towards fatty acids... 

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