3-hydroxyalkanoic acids from

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)...

A. Kaunzinger, M. Thomsen, A. Dietiich and A. Mosandl, Stereodifferentiation and simultaneous analysis of 2- and 3-hydroxyalkanoic acids from hiomemhranes by multidimensional gas clnomatography , 7. High Resolut. Chromatogr. 18 191-193 (1995). 

Timm, A. and Steinbuchel, A., 1990, Formation of polyester consisting of medium chain length 3-hydroxyalkanoic acid from gluconate by Pseudomonas aeruginosa and other fluorescent pseudomonads. Appl. Environ. Microbiol. 56 3360-3367... 

Lee, E. Y, Jendrossek, D., Schirmer,A., Choi, C. Y, Steinbuchel, A. Biosynthesis of copolyesters consisting of 3-hydroxybutyric acid and medium-chain-length 3-hydroxyalkanoic acids from 1,3-butanediol or from 3-hydroxybutyrate by Pseudomonas sp. A33. Appl Microbiol Biotechnol 1995a, 42, 901-909. 

Ramsay, B.A., Ramsay, J., Berger, E. et ai. (1992) Separation of poly-beta-hydroxyalkanoic acid from microbial biomass. US Patent 5110980. 

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. 

Aliphatic polyesters based on monomers other than a-hydroxyalkanoic acids have also been developed and evaluated as drug delivery matrices. These include the polyhydroxybutyrate and polyhydroxy valerate homo- and copolymers developed by Imperial Chemical Industries (ICI) from a fermentation process and the polycaprolactones extensively studied by Pitt and Schindler (14,15). The homopolymers in these series of aliphatic polyesters are hydrophobic and crystalline in structure. Because of these properties, these polyesters normally have long degradation times in vivo of 1-2 years. However, the use of copolymers and in the case of polycaprolactone even polymer blends have led to materials with useful degradation times as a result of changes in the crystallinity and hydrophobicity of these polymers. An even larger family of polymers based upon hydroxyaliphatic acids has recently been prepared by bacteria fermentation processes, and it is anticipated that some of these materials may be evaluated for drug delivery as soon as they become commercially available. 

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... 

The mechanism for bacterial synthesis of PHA is not the simple dehydration reaction between alcohol and carboxyl groups. It is more complicated and involves the coenzyme A thioester derivative of the hydroxyalkanoic acid monomer (produced from the organic feedstock available to the bacteria) [Kamachi et al., 2001], Growth involves an acyl transfer reaction catalyzed by the enzyme PHA synthase (also called a polymerase) [Blei and Odian,... 

Liu, S.J. Steinbuchel, A. Exploitation of butyrate kinase and phosphotransbutyrylase from Clostridium acetobutylicum for the in vitro biosynthesis of poly(hydroxyalkanoic acid). Appl. Microbiol. Biotechnol., 53, 545-552 (2000)... 

Ashby, R. D., Solaiman, D. K. Y., and Foglia, T. A. 2002. The synthesis of short- and medium-chain-length poly(hydroxyalkanoate) mixtures from glucose- or alkanoic acid-grown Pseudomonas oleovorans. J. Ind. Microbiol. Biotechnol., 28,147-153. 

A related route to a-hydroxyalkanoic acids is illustrated by the synthesis of / (-)-2-hydroxy-2-methylbutyric acid (407) from (5)(-)-tigloylproline (403). The initial step of halolactonization of 403 with N-bromosuccini-mide in DMF proceeds stereospecifically to give 405 (94.5%) and 407 (5.5%). Debromination of 405 to 409 with tributyltin hydride in benzene, followed by hydrolysis, gave the desired compound 410 (77TL1005 79T2337, 79T2345). 

The PHA produced by the transformed cyanobacterial cells was identified by GC-MS analysis. The constituents of PHA of the cyanobacterial cells were 3-hydroxybutyric acid, lactic acid, and other unknown hydroxyalkanoic acids, and the major constituent was p-hydroxybutyric acid. The average molecular weight (M.W.) of PHA produced by the cyanobacterial cells was about 1,000,000, similar to the average M.W. of PHA from Alcaligenes eutrophus. 

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. 

While the first efforts [11, 12] of the biotechnological generation of aliphatic homopolyesters and random copolyesters have been restricted essentially on monomers from 3-hydroxybutyric acid (3HB) and 3-hydroxypentanic acid (3HV), newer investigations concentrate on mraiomers with branches in the range of medium chain length, the so-called thermoplastic elastomers [13—15]. Steinbiichel et al. [3] catalogued more than 100 hydroxyalkanoic acids as craistituents of biosynthetic PHAs. 

The crystallization kinetics of native P(3-hydroxyalkanoic acid) (PHA) granules isolated from the strains of A. eutrophus and P. oleovorans have been studied by measurements of the glass-transition temperature with a differential scanning calorimeter [36]. The comparison is made between PHA in vivo and the isolated polymer. It is demonstrated that the native granules do not contain a plasticizer and the amorphous state of in vivo PHA can be explained by straightforward crystallization kinetics. 

There are several possible important factors which affect the cocrystalliz-ability of comonomer units with shorter side chains in c6poly(hydroxyalkanoic acid). These are such as the number of main-chain carbon atoms, the existence and the size of side-chains, steric configurations, crystallization temperature and the rate of crystallization. From a chemical point of view, the 3HP unit is expected to be easily incorporated into the P(3HB)-type crystalline lattice as a crystal component, since it has no side chain and its main chain consists of the same number of carbon atoms as the 3HB unit. 

It is interesting to investigate effects of long side chains on the molecular dynamics and related physical properties of poly(hydroxyalkanoic acid)s. The poly(hydroxyalkanoic acid)s with longer side chains, such as poly(3-hydroxyoctanoic acid) [P(3HO)], have quite different mechanical properties from P(3HB) and P(3HB-co-3HV), being thermal elastmers with low glass transition temperatures ranging from -25 to — 40°C [88] and a much lower crystallinity of about 25-33% [89]. 

Other remarkable differences of these two classes refer to the substrate specificities of the enzymes. Whereas class-I PhaCs, like the enzyme of Ralstonia eutropha, are restricted to 3-, 4-, and 5-hydroxyalkanoic acids of short-carbon-chain length (SCL), class-II PhaCs like the enzyme from Pseudomonas aeruginosa are restricted to 3-hydroxyalkanoic acids of medium-carbon-chain length (MCL). The enzyme of R. eutropha accepts also 3-mercaptoalkanoateSCL-CoA thioesters as substrates. 

P-Hydroxycarboxamides. Selective amidation of 3-hydroxyalkanoic acids is easily performed via formation and aminolysis of 2,2-bis(trifluoromethyl)-l,3-dioxan-4-ones/ The heterocycles are obtained from condensation of the hydroxy acids with hexafluoroacetone in the presence of iV,iV -diisopropylcarbodiimide. 

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