Β-hydroxyisobutyric Acid Research Articles

Microbial Stereoselective Oxidation of 2-methyl-1,3-propanediol to (R)-β-hydroxyisobutyric Acid in Aqueous/organic Biphasic Systems

The aim of this work was to evaluate (R)-g-hydroxyisobutyric acid (HIBA) production by microbial stereoselective oxidation of 2-methyl-1,3 propanediol under different conditions, and to compare the performance of this bioconversion in traditional aqueous media and aqueous/organic biphasic media. The oxidation is a two-step reaction with hydroxyisobutanal as an intermediate. Among the operational factors tested, pH and aeration were those, which most significantly affected the biocatalytic activity. Enantiomeric excesses higher than 95% were consistently obtained. For substrate concentrations above 50 mg ml−1 a slight substrate inhibition was observed. Product inhibition was much stronger, and together with the decrease of the pH during the bioconversion was the most important limiting factor in long-term bioconversions. Kinetic parameters were determined for different pH values. A compromise pH value of 4 was determined to be the optimum for HIBA production and simultaneous extraction with an organic phase of trioctyl phosphine oxide (TOPO) in isooctane.

Enhanced production of d-β-hydroxyisobutyric acid through strain improvement

The mutant strains of Candida rugosa were developed for enhanced enantioselective production of d(−)-β-hydroxyisobutyric acid ( D-HIBA) from isobutyric acid (IBA). Three mutant strains, C. rugosa MME 1027, MME 1259 and MME 1559, which can not assimilate propionic acid, were screened. The molar conversion yield and D-HIBA productivity were compared in fed-batch cultivations of the mutant strains. The maximum D-HIBA concentration of 150 g l −1 with the highest molar conversion yield of 81.8% was achieved with the strain MME 1259, while the highest productivity of 1.1 g l −1 h −1 was obtained with the strain MME 1027.

Strain development for the production of D(−)-β-hydroxyisobutyric acid

Candida rugosa BR-120, which cannot catabolize D(−)-β-hydroxyisobutyric acid (D-HIBA), was developed fromCandida rugosa IFO 0750 by UV irradiationC. rugosa BR-120 could not assimilate propionic acid as a carbon source. It is presumed thatC. rugosa BR-120 lacks HIBA dehydrogenase.C. rugosa BR-120 produced D-HIBA from isobutyric acid (IBA) with a high yield about 94%, whileC. rugosa IFO 0750 did it with about 42% on 5 days batch cultivation. On 5 days fed-batch cultivation,C. rugosa BR-120 andC. rugosa IFO 0750 produced 12.45 g/L and 5.22 g/L of D-HIBA, respectively. The degradation rate of D-HIBA by the resting cell ofC. rugosa IFO 0750 was 31.95%, butC. rugosa BR-120 was 3.08% on 2 days incubation.

Complex-forming equilibria in isotachophoresis : VI. simulation of isotachophoretic equilibria of lathanoids and determination mobilities and stability constants of acetate and β-hydroxyisobutyrate complexes

The istachophoretic separation of fourteen lanthanoids (Ln) was studied using three difeerent electrolyte systems, viz., acetic acid (Ac), β-hydroxyisobutyric acid (HIB) and their mixture, as the complexing agent. A computational procedure based on the least-squares technique was used for the determination of the absolute mobilities of LnAc, LnHIB and Ln(HIB)Ac complexes from the qualitative index R E. The stability constants of Ln(HIB)Ac were also determined. Using the determ constants, the isotachophoretic separation of lanthanoids could be explained by the differences in the effective mobilities accompanied by the different abundances of multi-coordinated complexes.

Enantioselective synthesis of β-hydroxyisobutyric acid: a useful synthon in the synthesis of polypropionate-type natural products

The aldol reaction of formaldehyde with the dicyclopentylborinyl enolate derived from S -(or R -) 1-tert-butyldimethylsilyloxy-l-cyclohexylbutan-2-one, followed by desilylation and sodium meta-periodate oxidation, provides R -(or S -) β-hydroxyisobutyric acid.

ChemInform Abstract: ENANTIOTOPICALLY SELECTIVE OXIDATION OF 1,3‐DIOLS WITH A MICROORGANISM

Microbial oxidation of 2-methylpropane-1,3-diol (1a) proceeded with distinction of pro-(R) and pro-(S) hydroxymethyl groups resulting in the formation of β-hydroxyisobutyric acid (2a) of high optical purity. 2-Ethyl and 2-isopropyl derivatives (1b, c) were also oxidized to give the corresponding hydroxy acids (2b, c), but the optical yields were low.

ENANTIOTOPICALLY SELECTIVE OXIDATION OF 1,3-DIOLS WITH A MICROORGANISM

Abstract Microbial oxidation of 2-methylpropane-1,3-diol (1a) proceeded with distinction of pro-(R) and pro-(S) hydroxymethyl groups resulting in the formation of β-hydroxyisobutyric acid (2a) of high optical purity. 2-Ethyl and 2-isopropyl derivatives (1b, c) were also oxidized to give the corresponding hydroxy acids (2b, c), but the optical yields were low.

Metabolism of valine in cultured human skin fibroblasts

1. 1. The pathway of valine metabolism in human cultured skin fibroblasts has been explored with the use of 14C differentially labeled substrates. These include [1- 14C]valine, DL-[2- 14C]valine, DL-[4- 14C]valine, and [1- 14C]isobutyric, [2- 14C]isobutyric, [1- 14C]propionate and 2[- Me- 14C]methylmalonic acids. The rates of 14CO 2 production in cells derived from normal individuals and from patients affected with propionic acidemia and methylmalonic aciduria were compared. 2. 2. Results showed that nearly normal amounts of labeled CO 2 were liberated using [2- 14C]valine and [1- 14C]isobutyric acid by patient cells. Additional studies have suggested that the pathway of valine metabolism is via propionyl-CoA as an obligated intermediate presumably derived from methylmalonyl semialdehyde, rather than the direct conversion of methylmalonyl semialdehyde tomethylmalonyl-CoA without the participation of propionate. 3. 3. Substantial amounts of labeled intermediate, β-hydroxyisobutyric acid were detected in all valine and isobutyrate incubations. These findings suggest that the conversion of β-hydroxyisobutyrate to methylmalonyl semialdehyde, a NAD-dependent reaction, is the rate-limiting step of valine metabolism.

Stereochemistry of the conversion of methacrylate to beta-hydroxyisobutyrate in Pseudomonas putida.

Stereospecifically labelled (2S,3S+ 2R,3R)-[2,3-2H2]-β-hydroxyisobutyric acid methyl ester benzoate was synthesized and used to assign the Eu(fod)3 shifted n.m.r. signals of the C-3 hydrogens of the unlabelled analogue. (E)-[3-2H1]Methacrylic acid was converted by Pseudomonas putida(ATCC 21244) to (2S,3S)-[3-2H1]-β-hydroxyisobutyric acid. The results show that the hydration of methacrylate to S-(+)-β-hydroxyisobutyric acid in this organism, probably via methacrylyl-CoA, proceeds stereospecifically by syn hydration.

A stereochemical study on the metabolism of isobutyrate in Pseudomonas putida

Ammonium[2- 3H,1- 14C]isobutyrate was converted by Pseudomonas putida ATCC 21244 into S(+)-β-hydroxyisobutyric acid (β-HIBA) with loss of the α-tritium atom. The recovered isobutyrate had the same 3H 14C as the starting material. Ammonium (2 S)-[3- 13C]isobutyrate was synthesized and converted by P. putida into β-HIBA. The 13C-nmr of the corresponding methyl ester benzoate showed 13C enrichment in the hydroxymethyl carbon atom. The results therefore indicate that isobutyrate metabolism in this organism proceeds via an unsaturated intermediate (probably methacrylyl-CoA) formed by dehydrogenation of the 2- pro-S-methyl group of the precursor (isobutyryl-CoA). Hydration of the intermediate proceeds with addition of a proton at C-2 from the same side as the hydrogen removed in the dehydrogenation.

Preparation of (R)-β-Hydroxyisobutyric Acid from threo-3-Methyl-l-aspartate

(-)-(R)-β-Hydroxyisobutyric acid N-phenylcarbamate was prepared from threo-3-methyl- l -aspartic acid (Scheme 1). The configuration of threo-3-methyl- l -aspartic acid was confirmed by direct correlation with (S)-methylsuccinic acid. The configurations of the two racemates of 2-bromo-3-methylsuccinic acid have been established.

The Absolute Configuration of Methylmalonyl Coenzyme A and Stereochemistry of the Methylmalonyl Coenzyme A Mutase Reaction

Abstract Propionyl coenzyme A was carboxylated with epimerase-free carboxylase, and the resulting methylmalonyl coenzyme A (a) was reduced with Raney nickel. Isolation of (-)-(R)-β-hydroxyisobutyric acid N-phenylcarbamate (11) from the reaction mixture showed that methylmalonyl coenzyme A (a) has the (S) configuration. Propionyl coenzyme A was also converted to deuteriosuccinate with a D2O extract of a beef liver mitochondrial acetone powder. The deuteriosuccinate had a plain positive optical rotatory dispersion curve corresponding to the (S) configuration. It was concluded that (S)-methylmalonyl coenzyme A, formed by carboxylation of propionyl coenzyme A, was epimerized in D2O to (RS)-methylmalonyl(coenzyme A)-2-D, and that (R)-methylmalonyl(coenzyme A)-2-D was isomerized to succinyl coenzyme A with net retention of configuration of C-2. Since, in contrast, the glutamate mutase reaction proceeds with inversion, the lack of stereochemical uniformity in these two otherwise closely related rearrangements suggests that they may involve at least two steps, one or more of which are analogous, but at least one taking place with different stereochemistry. It is suggested that the cobamide coenzyme releases an electrophilic 5'-deoxyadenosyl group (perhaps reversibly to a methionyl residue on the enzyme), and that the resulting Co:i complex participates in the rearrangement by removal and transfer of a proton or other cationic fragment.