2-hydroxyalkanoic acid 2-hydroxyalkanoate ester

Figure 15.7 Cliromatographic separation of cliiral hydroxy acids from Pseudomonas aeruginosa without (a) and with (h) co-injection of racemic standards. Peak identification is as follows 1, 3-hydroxy decanoic acid, methyl ester 2, 3-hydroxy dodecanoic acid, methyl ester 3, 2-hydroxy dodecanoic acid, methyl ester. Adapted from Journal of High Resolution Chromatography, 18, A. Kaunzinger et al., Stereo differentiation and simultaneous analysis of 2- and 3-hydroxyalkanoic acids from hiomemhranes hy multidimensional gas cliromatog-raphy , pp. 191 -193, 1995, with permission from Wiley-VCH. (continuedp. 419)...

An efficient method for the depolymerization of poly-[(i )-3-hydroxybutanoic acid esters] has been reported. 3-Hydroxyalkanoic esters have been prepared from the corresponding ketones by catalytic hydrogenation, using a Raney nickel catalyst that is modified by (R,R)-tartaric acid and NaBr the average optical yield is 85 %. ... 

By simply hydrolyzing the easily accessible 2-hydroxy-2-methylalkanenitriles with concentrated acid, 2-hydroxy-2-methylalkanoic acids are obtained without measurable racemization (Table 3). The reaction sequence from the starting ketone to the carboxylic acid can be carried out in one pot without isolation of the cyanohydrin. The enantiomeric excesses of the (/ )-cyanohydrins and the (ft)-2-hydroxyalkanoic acids are determined from the ( + )-(/T)-Mosher ester derivatives and as methyl alkanoates by capillary GC, respectively. The most efficient catalysis by (R)-oxynitrilase is observed for the reaction of hydrocyanic acid with 2-alkanoncs. 3-Alkanoncs are also substrates for (ft)-oxynitrilase, to give the corresponding (/ )-cyanohydrins32. 

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. 

Zeolites have also been described as efficient catalysts for acylation,11 for the preparation of acetals,12 and proved to be useful for acetal hydrolysis13 or intramolecular lactonization of hydroxyalkanoic acids,14 to name a few examples of their application. A number of isomerizations and skeletal rearrangements promoted by these porous materials have also been reported. From these, we can underline two important industrial processes such as the isomerization of xylenes,2 and the Beckmann rearrangement of cyclohexanone oxime to e-caprolactam,15 which is an intermediate for polyamide manufacture. Other applications include the conversion of n-butane to isobutane,16 Fries rearrangement of phenyl esters,17 or the rearrangement of epoxides to carbonyl compounds.18... 

Reaction of esters of hydroxyalkanoic acids with sulfur tetrafluoride, unless forcing conditions arc applied, generally results in selective replacement of the hydroxy group by fluorine to give almost equimolar mixtures of fluoroalkanoates 3 and alkoxycarbonylalkyl fluorosulfites 4 in high total yield.65... 

Carboxylic esters, especially lactones, are conveniently obtained via the pyridyl thioesters (18). Some examples are given in Scheme 1. The 2-pyridyl thiol ester method can be further improved if silver ions (AgC104) are used as activators. Corey and Brunelle have also introduced other heterocyclic disulfides, and (19) was found to be superior to other reagents tested for the formation of lactones from w-hydroxyalkanoic acids. 

Until recently, access to optically active 3-hydroxyalkanoates by enantioselective transition metal catalysis was based primarily on the heterogeneous hydrogenation of 3-oxo esters by Raney nickel modified with tartaric acid and sodium bromide (see Section 2.3.1.1.). As far as homogeneous catalysis is concerned, the best optical induction (71 % ee) in the hydrogena-... 

The methyl 3-hydroxyalkanoates can be transformed into optically pure compounds. Thus, the esters were hydrolyzed to the corresponding acids, and the dicyclohexyl ammonium salts were recrystallizcd from acetonitrile. Three recrystallizations gave the optically pure 3-hydroxyalka-noic acids in 50-75% yield67. In some cases, the dibenzyl ammonium salts were superior to the dicyclohexyl ammonium salts, e g., for 3-hydroxybutanoic acid, which was obtained optically pure after two recrystallizations from acetonitrile68. 

Various enantiomerically pure (/ )-3-hydroxyalkanoic acids (RHA) can be conveniently prepared by depolymerizing the biosynthesized PHA. De Roo et al. (2002) produced the chiral RHA and RHA methyl esters via hydrolytic degradation of PHA synthesized by pseudomonads. They first hydrolyzed the recovered PHA by acid methanolysis and then distilled the RHA methyl ester mixture into several fractions. Subsequently, the RHA methyl esters were saponified to yield the corresponding RHA with final yields of the RHA up to 92.8% (w/w). 

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