Citramalate

S. Except for oxido-reductases, transferases, and hydrolases, most ligases (enzymes that catalyze bond formation) are entirely substrate specific. Thus, fumarate hydratase (or fumarase) reversibly and stereospecifically adds water to fumaric acid to produce (S)-( — )-malic acid only (8) (Figure 1), and another enzyme, mesaconase, adds water to mesaconic acid to form (+ )-citramalic acid (9) (Figure 2). Although no extensive studies are available, it appears that neither fumarase nor mesaconase will add water stereospecifically to any other a,(3-unsaturated acid. 

Barker, H. A. Blair, A. H. Biochem. Prep. 1962, 9, 21. See also Hulme, A. C. Biochim. Biophys. Acta 1954, 14, 36, for a suggestion that (- )-citramalic acid occurs in nature. 

This enzyme [EC 4.1.3.25] catalyzes the conversion of (35)-citramalyl-CoA to acetyl-CoA and pyruvate. The (35)-citramalyl thioacyl-carrier protein can also be utilized as a substrate. This enzyme has been reported to be a component of citramalate lyase [EC 4.1.3.22]. 

STEREOCHEMICAL TERMINOLOGY, lUPAC RECOMMENDATIONS CITRAMALATE LYASE CITRAMALYL-GoA LYASE GITRATE LYASE GITRATE SYNTHASE L-Citrulline,... 

Among the compounds commonly determined in research laboratories are diacetyl, 2,3-butandiol, glycerol, citramalic acid, amino acids (especially proline), histamine, ammonia, succinic acid, phosphate, ash, alkalinity of the ash, ethyl, acetate, methyl anthranilate, total volatile esters, higher alcohols (both total and individually) phenolic compounds, etc. An elegant method for determining ethyl esters, capronate, caprylate, caprinate, and laurate using carbon disulfide extraction and GLC has been published (123). 

Tartaric, malic, citric, pyruvic, succinic, lactic, acetic, shikimic, galacturonic, citramalic Wine AMINEX HPX 87H (300 X 7.8 mm) 45°C 0.0075 M h2so4 UV, 210 nm 24... 

Bromal (25.0 g 89.1 mmol) and (S)-citramalic acid (11.0 g 74.2 mmol) were cooled to 0°C under inert atmosphere. Sulfuric acid/acetic acid (1/1 25 ml) was added dropwise with stirring. After 2 h the contents were a yellow solution with a white precipitate. The ice bath was removed and the reaction mixture was stirred overnight at room temperature. The reaction mixture was diluted with ice and extracted 4 times with ethyl acetate. The organic layer was back extracted with water and then was dried with MgS04. After filtration, the filtrate was concentrated to an oil. The product was obtained as a white solid after crystallization from toluene/hexanes. Yield 23.2 g (77%) mp 151°C (sublime). 

The cycloaddition of ketene with chloral in the presence of catalytic quantities of quinidine or quinine leads to the oxetanones in high optical and chemical yield (Scheme 26.22). This reaction is practiced on an industrial scale with the chiral building blocks malic and citramalic acids being formed by hydrolysis.492... 

Citramalic acid (= 2- Malus domestica (apple peel) (Rosaceae) Sour (acid) taste... 

Quantitative recoveries of tartaric, malic, citric, citramalic and succinic acids are achieved, and are higher than 90% for acetic and... 

By using both C18 and Aminex HPLC column, succinic, citramalic and fumaric acid can also be determined in the same run of the other organic acids. With C18 columns, these compounds exit in the chromatogram after citric acid in the sequence succinic-citramalic-fumaric in the chromatogram using the Aminex column, succinic acid exits close to shikimic acid, the fumaric acid peak falls between those of lactic acid and acetic acid. 

Reaction with trichloroacetone is similarly high-yielding and enantioselective giving the p-lactone 172 and after hydrolysis with inversion, (.S )-citramalic acid 173. Again, quinine gives the other enantiomer. 

Figure 8. Kinetics data for organic synthesis reactions in the citric acid-water system at 200°C and 200 MPa, the results show decay of citric acid coupled with synthesis of various carboxylic acids (CA citraconic acid CM citramalic and paraconic acids). Note that because of the phase separation of CO2 from the aqueous phase, the data here reflect the solubility of CO2 in the aqueous phase at these conditions.

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