3-Hydroxy fatty acids, synthesis

At the end of the reaction, hydroperoxide can be easily recovered in the aqueous phase (98-99%) after its separation from the organic phase and precipitation of the enzymes. The hydroperoxides obtained are highly reactive molecules [109]. They are intermediate compounds in the lipoxygenase pathway in plants, precursors for the synthesis of hydroxy-fatty acids (i.e., ( + )-coriolic acid [38,110], and regulators of the prostaglandins biosynthesis [111-113]. 

FIGURE 3-7 Pathways for the interconversion of brain fatty acids. Palmitic acid (16 0) is the main end product of brain fatty acid synthesis. It may then be elongated, desaturated, and/or P-oxidized to form different long chain fatty acids. The monoenes (18 1 A7, 18 1 A9, 24 1 A15) are the main unsaturated fatty acids formed de novo by A9 desaturation and chain elongation. As shown, the very long chain fatty acids are a-oxidized to form a-hydroxy and odd numbered fatty acids. The polyunsaturated fatty acids are formed mainly from exogenous dietary fatty acids, such as linoleic (18 2, n-6) and a-linoleic (18 2, n-3) acids by chain elongation and desaturation at A5 and A6, as shown. A A4 desaturase has also been proposed, but its existence has been questioned. Instead, it has been shown that unsaturation at the A4 position is effected by retroconversion i.e. A6 unsaturation in the endoplasmic reticulum, followed by one cycle of P-oxidation (-C2) in peroxisomes [11], This is illustrated in the biosynthesis of DHA (22 6, n-3) above. In severe essential fatty acid deficiency, the abnormal polyenes, such as 20 3, n-9 are also synthesized de novo to substitute for the normal polyunsaturated acids. 

By 1960 it was clear that acetyl CoA provided its two carbon atoms to the to and co—1 positions of palmitate. All the other carbon atoms entered via malonyl CoA (Wakil and Ganguly, 1959 Brady et al. 1960). It was also known that 3H-NADPH donated tritium to palmitate. It had been shown too that fatty acid synthesis was very susceptible to inhibition by p-hydroxy mercuribenzoate, TV-ethyl maleimide, and other thiol reagents. If the system was pre-incubated with acetyl CoA, considerable protection was afforded against the mercuribenzoate. In 1961 Lynen and Tada suggested tightly bound acyl-S-enzyme complexes were intermediates in fatty acid synthesis in the yeast system. The malonyl-S-enzyme complex condensed with acyl CoA and the B-keto-product reduced by NADPH, dehydrated, and reduced again to yield the (acyl+2C)-S-enzyme complex. Lynen and Tada thought the reactions were catalyzed by a multifunctional enzyme system. 

We then focused on the synthesis of lipid A analogs which contain 3-hydroxy fatty acids. For this purpose, sufficient amount of (R)-3-hydroxytetradecanoic acid ( ), which is the commonest hydroxy acid in Salmonella lipid A, was first prepared by means of an asymmetric reduction of the corresponding keto ester, i. ., methyl 3-oxotetradecanoate (j ) (7). Catalytic hydrogenation of 21 in the presence of Raney Ni modified with (R, R)-tartaric acid foaBr (8) afforded the crude (R)-ester in 85% enantiomeric excess. After saponification, the resultant acid was purified through its dicyclohexylammonium salt to give the optically and chemically pure (R)-acid In a yield of 61% from... 

Aveldano, M.I. and Sprecher, H. (1983). Synthesis of hydroxy fatty acids from 4,7,10,13, 16, 19- (l-C-14) docosohexaenoic acid by human platelets. Journal of Biological Chemistry 585,9339-9343. 

Each of the enzymatic activities located in a single polypeptide chain of the mammalian fatty acid synthetase exists as a distinct protein in E. coli. The acyl-carrier protein (ACP) of E. coli has an Mr = 8,847 and contains 4-phosphopantotheine. The dehydratase has a molecular weight of 28,000 and catalyzes either trans 2-3 or cis 3-4 dehydration of the hydroxy acid intermediates in the biosynthesis of palmitic acid. When the chain length of the hydroxy fatty acid is C[ the synthesis of palmitoleic acid is achieved as follows ... 

In known metabolic states and disorders, the nature of metabolites excreted at abnormal levels has been identified by GC-MS. Examples of this are adipic and suberic acids found in urine from ketotic patients [347], 2-hydroxybutyric acid from patients with lactic acidosis [348], and methylcitric acid (2-hydroxybutan-l,2,3-tricarboxylic acid) [349] in a case of propionic acidemia [350,351]. In the latter instance, the methylcitric acid is thought to be due to the condensation of accumulated propionyl CoA with oxaloacetate [349]. Increased amounts of odd-numbered fatty acids present in the tissues of these patients due to the involvement of the propionyl CoA in fatty acid synthesis, have also been characterised [278]. A deficiency in a-methylacetoacetyl CoA thiolase enzyme in the isoleucine pathway prevents the conversion of a-methylacetoacetyl CoA to propionyl CoA and acetyl CoA [352,353]. The resultant urinary excretion of large amounts of 2-hydroxy-3-methylbutanoic acid (a-methyl-/3-hydroxybutyric acid) and an excess of a-methylacetoacetate and often tiglyl glycine are readily detected and identified by GC-MS. 

This transport is accomplished by carnitine (L-jS-hydroxy-y-trimethylammonium butyrate), which is required in catalytic amounts for the oxidation of fatty acids (Figure 18-1). Carnitine also participates in the transport of acetyl-CoA for cytosolic fatty acid synthesis. Two carnitine acyl-transferases are involved in acyl-CoA transport carnitine palmitoyltransferase I (CPTI), located on the outer surface of the inner mitochondrial membrane, and carnitine palmitoyltransferase II (CPTII), located on the inner surface. 

This reaction is also a route for the synthesis of hydroxy fatty acids. The a-hydroxy fatty acid can be further... 

Valentin, H.E., and Steinbtichel, A. (1994) Application of enzymatically synthesized short-chain-length hydroxy fatty acid coenzyme A thioesters for assay of polyhydroxyalkanoic acid synthesis. Appl. Microbiol. Biotechnol., 40, 699-709. 

Malonyl-ACP, formed from acetyl-CoA (shuttled out of mitochondria) and CO2, condenses with an acetyl bound to the Cys—SH to yield acetoacetyl-ACP, with release of CO2. This is followed by reduction to the n-/3-hydroxy derivative, dehydration to the trans-t -unsaturated acyl-ACP, and reduction to butyryl-ACP. NADPH is the electron donor for both reductions. Fatty acid synthesis is regulated at the level of malonyl-CoA formation. 

Degradation of fatty acids proceeds via an inducible set of enzymes that catalyze the pathway of P-oxidation [18]. P-Oxidation occurs via repeated cycles of reactions that are essentially the reverse of the reactions of fatty acid synthesis (Fig. 8). However, three major differences distinguish the two pathways. First, P-oxidation utilizes acyl-CoA thioesters and not acyl-ACPs. Second, the P-hydroxy intermediates have the opposite stereochemistry (L in P-oxidation and d in synthesis). Finally, the enzymes of P-oxidation share no homology with those of synthesis. 

In p-oxidation, FAD is the coenzyme for the first oxidation reaction, while NAD is the coenzyme for the second. In fatty-acid synthesis, NADPH is the coenzyme for both. The p-hydroxy-acyl group in p-oxidation has the L-configuration, while it has the D-configuration in fatty acid synthesis. 

Plusbacin Aj (21) and the derivatives A2-A4 and B1-B4 are lipodepsipeptides isolated from a strain numbered PB-6250 related to the genus Pseudomonas obtained from a soil sample collected in the Okinawa Pref., Japan [56]. These compounds contain arginine residue and lactone linkage with characteristic 3-hydroxy fatty acids [57] (Figure 10.6). Plusbacin A3 (22) showed inhibitory activity against methicilhn resistant Staphylococcus aureus [56,58]. Recent total synthesis of this compound was reported and the absolute configuration of the lactone residue was determined as R [59]. 

This review eovers work published during the past six years (1993-1998) on the syntheses of an array of special fatty acids and their derivatives. It can be regarded as an extension to the review on the synthesis of rare and unusual fatty acids (1). We have also published two recent reviews on fatty acids, fatty acid analogs, and their derivatives (2,3). This review does not cover the synthesis of prostaglandins, prostacyclins, thromboxanes, and leukotrienes (lipoxins) however, the syntheses of some polyunsaturated hydroxy fatty acids are discussed. 

Fig. 19. Schematic depiction of the enterohepatic circulation of bile acids in patients with severe impairment in bile acid absorption. Decreased absorption causes increased hepatic synthesis, which is inadequate to restore the bile acid pool size to normal. The concentration of bile acids in the jejunum during digestion is below the critical micellar concentration, and the resultant fat digestion, as well as decreased intestinal surface area, causes fat malabsorption. The unabsorbed fatty acids or their bacterial degradation products, hydroxy fatty acids, or both induce water secretion. Bacterial changes in the colon appear to remove bile acids from solution, so that these patients have a fatty acid diarrhea and not a bile acid diarrhea (115). These patients have been termed decompensated. ...

In summary, it is now clear that unsaturated fatty acids serve as substrates for the synthesis of a variety of different prostaglandins, hydroxy fatty acids, and leukotrienes. The types and amounts of these compounds produced will in part depend on what type of dietary fat is included in the diet. In turn, the factors regulating the desaturation and chain elongation of fatty acids for subsequent incorporation into and release from phospholipids will contribute in defining what types and amounts of prostaglandins are produced to mediate and control physiological processes. 

Most of the mcl-PHA production strains - with the exception of Pseudomonas putida GPol - accumulate alkanoic mcl-PHA also from unrelated carbon substrates through the fatty acid de novo synthesis pathway. Consequently, glucose may result in polymers containing (R)-3-hydroxy fatty acids with even carbon numbers, e.g., (R)-3-hydroxydecanoate, (R)-3-hydroxyoctanoate, (R)-3-hydroxyhexanoate,... 

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