Hydroxyacids and Derivatives

Camauba wax is obtained from the leaves of several species of palm trees in South America, such as Copemicia cerifem which grows in Brazil. It is made up of esters of long chain alcohols and acids with high carbon number, high molecular weight polyesters of hydroxyacids, and derivatives of p-hydroxy- and p-methoxycinnamic acid [84]. 

An alternative to the extraction of intact PHA polymer is the isolation of PHA monomers, oligomers, or various derivatives such as esters [74]. PH As are composed of stereo-chemically pure P-3-hydroxyacids, and therefore can be used as a source of optically pure organic substrates for the chemical and pharmaceutical industry [79]. In this protocol, the defatted cake containing PHA polymer would be chemically treated to obtain the PHA derivatives. For example, transesterification of the meal with methanol would give rise to methyl esters of 3-hydroxyalkanoic acids. The PHA derivatives would then be separated from the meal with appropriate solvents. One potential disadvantage of this method is the potential alteration of the quality of the residual meal if the harsh chemical treatments required for the production of PHA derivatives lead to protein or amino acid breakdown. 

The gas chromatographic separation of enantiomers or diastereoisomeric. derivatives, of 4-hydroxyacids and... 

Table IV. Separation Data for the Capillary GC-Separation of R-(+)-Phenylethylurethanes of 4-and 5-Hydroxyacid Esters Derived from Chiral...

Hydroxyacid esters are contained in several subtropical fruits like pineapple (26), passion fruit (27) and mango (2 ). 3-Hydroxyacid derivatives are formed as intermediates during de novo synthesis and P -oxidation of fatty acids, but the two pathways lead to opposite enantiomers. S-(+)-3-Hydroxyacyl-CoA-esters result from stereospecific hydration of 2,3-trans-enoyl-CoA during P -oxidation R-(-)-3-hydroxyacid derivatives are formed by reduction of 3-ketoacyl-S-ACP in the course of fatty biosynthesis. Both pathways may be operative in the production of chiral 3-hydroxyacids and 3-hydroxyacid esters in tropical fruits. 

During aging of PHVB in sterile water at pH 7 and 60 °C, 2-butenoic acid (crotonic acid), 2-pentenoic acid, 3-hydroxybutyric acid, 3-hydroxyvaleric acid, 3-hydroxybutyrate dimer, 3-hydroxybutyrate-3-hydroxyvalerate dimer and 3-hydroxyvalerate dimer were formed [99]. The weight loss was, however, only 2% after 200 days at 60 °C. Monomers, oligomers and derivatives, produced by dehydration at the OH-terminus were identified after alkaline hydrolysis of PHB [110]. In accordance CZE showed that the accelerated hydrolysis of PHB leads to the formation of hydroxyacid oligomers and a series of peaks formed by a side reaction leading to a C=C bond at the noncarboxylic acid end [111]. Kinetics of the abiotic hydrolysis of PHB in acid and alkaline media were monitored by following the forma-... 

Polyesters with higher aromatic content such as LCP are made via an alternative route. Because they are phenolic esters, they cannot be made by direct ester exchange between a diphenol and a lower dialkyl ester due to unfavourable reactivities. The usual method is reverse ester exchange or acidolysis reaction [38] where the phenolic hydroxyl groups are acylated with a lower aliphatic acid anhydride, and this ester is heated with an aromatic dicarboxylic acid, with or without catalyst. Many of these polymers are derived from hydroxyacids, and their acetates readily undergo self-condensation in the melt, stoichiometric balance being inherent to the reaction [39, 40]. 

The major components of the C16 cutins are 9- or 10,16-dihydroxyhexadecanoic acid, and 16-hydroxyhexadecanoic acid. 16-Hydroxy-10-oxo-C16 acid and 16-oxo-9 or 10-hydroxy C16 acid are monomers in only some cases. The major components of the C18 family of monomers are 18-hydroxy-9,10-epoxyoctadecanoic acid and 9,10,18-trihydroxyoctadecanoic acid, together with their monounsaturated homologs. Omega hydroxyacids and their derivatives are the main components of cutin, which are interhnked via ester bonds, forming a polyester polymer of indeterminate size [211]. 

The most frequently studied organic acids are a-hydroxyacids, such as glycolic, citric, lactic, tartaric, etc. Glycyrrhizic and glycyrrhetinic and others can also be determined. Most of the methods are based on the use of LC. CE, GC, infrarred spectrometry (IR) and other techniques are sometimes used. Fatty acids and derivatives are determined by GC or LC. 

TV-Acyl indoles derived from amides have been employed for the conversion of lactones into protected hydroxyacids. Thus, (chloromethyl)alumi-num 2-(2-propenyl)anilide reacts (120) with 1,4- and 1,5-lactones, as for example per-O-terZ-butyldimethylsilyl-D-ribono-1,4-lactone (104), to afford hydroxyamides. After protection of the free hydroxyl group, these amides were converted by ozonolysis into TV-acyl indoles, 105, which were readily saponified to the acid 106. 

The procedure was proved to be general for the preparation of protected hydroxy acids from lactones (121). This apparently trivial process is often difficult to carry out, as the attempted derivatization of y or J-hydroxyacids frequently results in relactonization rather than hydroxyl protection. The method was applied to several aldonolactones to produce the corresponding intermediate hydroxyamides. Protection using [(2-trimethylsilyl)-ethoxy]methyl chloride, methoxymethyl chloride, ter/-butylchlorodimeth-ylsilane, or zm-butylchlorodiphenylsilane followed by ozonolysis gave the protected N-(y- or <5-hydroxyacyl)indole derivatives. Mild saponification gave indole and the acetal- or silyl-protected hydroxy acids. 

The reduction of 2-oxoacids bound to different chiral auxiliaries gave the 2-hydroxyacid derivatives in a 64 to 76% yield and 42 to 86% de depending on solvent, proton donor, supporting electrolyte, temperature, and substituent R in the oxoacid. The results are in accordance with an ECE reduction of the 2-oxoamide to an enolate anion, which subsequently undergoes a face-selective protonation to the hydroxy acid [346, 347]. 

Making use of a O-trityl-hydroxylamine linker, Meloni and Taddei reported the first example of Miller hydroxamate on solid phase (161, Scheme 73). /1-Lactams 162 and 163 were prepared on solid support starting from serine, threonine or other / -hydroxyacids derived from naturally occurring amino acids and a resin bonnd hydroxylamine 159. The ring closure of 160 was carried out under Mitsunobu conditions. 

A closely related E. coli protein is a 79-kDa multifunctional enzyme that catalyzes four different reactions of fatty acid oxidation (Chapter 17). The amino-terminal region contains the enoyl hydratase activity.32 A quite different enzyme catalyzes dehydration of thioesters of (3-hydroxyacids such as 3-hydroxydecanoyl-acyl carrier protein (see Eq. 21-2) to both form and isomerize enoyl-ACP derivatives during synthesis of unsaturated fatty acids by E. coli. Again, a glutamate side chain is the catalytic base but an imidazole group of histidine has also been implicated.33 This enzyme is inhibited irreversibly by the N-acetylcysteamine thioester of 3-decynoic acids (Eq. 13-8). This was one of the first enzyme-activated inhibitors to be studied.34... 

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