Acetolactic acid

Condensation 9 Acetaldehyde to acetoin. acetaldehyde to pyruvic acid to alpha-acetolactic acid. 

Richelieu, M., Hoalberg, U., and Nielsen, J. C. (1997). Determination of a-acetolactic acid and volatile compounds by head-space gas chromatography. ]. Dairy Sci. 80, 1918-1925. 

D- or L-lactic acid -- pyruvic acid ------------ - a-acetolactic acid... 

Another early success in biomimetic chemistry concerns reactions promoted by thiamin. In 1943, more than 35 years ago, Ukai, Tanaka, and Dokowa (12) reported that thiamin will catalyze a benzoin-type condensation of acetaldehyde to yield acetoin. This reaction parallels a similar enzymic reaction where pyruvate is decarboxylated to yield acetoin and acetolactic acid. Although the yields of the nonenzymic process are low, it is clearly a biomimetic process further investigation by Breslow, stimulated by the early discovery of Ugai et al., led to an understanding of the mechanism of action of thiamin as a coenzyme. 

Low Molecular Weight Carbonyl Compounds. In the dairy field, a major product made this way is starter distillate. The main component is diaceyl which is a very important aroma compound responsible for the characteristic buttery flavor of fermented dairy products such as sour cream or buttermilk. The dairy industry relies upon fermentation by lactic streptococci for the production of diacetyl in cultured products. Starter distillate is a natural product rich in diacetyl which is produced by distilling such lactic cultures. The key intermediate in the biosynthesis of diacetyl is aL-acetolactic acid which is decarboxylated to form diacetyl (Figure 3). The starting material of the biosynthetic pathway is citrate which is a natural component of milk. 

Biosynthesis Leu is formed from pyruvic acid - 2-acetolactic acid [acetolactate synthase (EC 4.1.3.18.)+(l-hydroxyethyl)-TPP] - 2,3-dihydroxy-isovaleric acid [reductase+NAD(P)H] - 2-oxoisova-leric acid [dihydroxyacid dehydratase] - 2-isopropyl-malate [2-isopropylmalate synthase + acetyl-CoA (EC 4.1.3.12)] -> 3-isopropylmalate [isopropylmalate dehydratase (EC 4.2.1.33) -HjO+HiO] 2-oxo-isocaproate [3-isopropylmalate dehydrogenase (EC 1.1.1.85) + NAD ] L. [leucine aminotransferase (EC... 

Biosynthesis In microorganisms and plants from pyruvic acid 2 pyruvate- 2-acetolactic acid (acetolactate synthase, EC 4.1.3.18 coenzyme thiamin(e) diphosphate)- 2,3-dihydroxyisovaleric acid (2-acetolactate mutase, EC 5.4.99.3)- 2-oxoisovaleric acid (dihydroxy acid dehydratase, EC 4.2.1.9). This is finally am-inated by branched chain amino acid aminotransferase (EC 2.6.1.42). 2-Oxoisovaleric acid is also a precursor of Leu. 

A second enzyme decarboxylates a-acetolactic acid. The enzyme is O OH O OH... 

Formate is the usual end product in polyalcohol fermentation by propionibacteria (Wawskiewich, 1968). Many propionibacteria produce significant amounts of acetoin and diacetyl (Antila, 1956/1957 Lee et al., 1969, 1970). The yield of diacetyl at 2TC is higher than at 32 C or 37T (Lee et al., 1969, 1970), the pH-optimum for its formation is pH 4.0-4.5. Diacetyl is reduced to acetoin and 2,3-butylenediol. Addition of citrate to the milk increases the yield of diacetyl and delays its conversion to reduced products. In small quantities acetaldehyde is also formed (Keenan and Bills, 1968). It is suggested (Antila, 1956/1957) that these products are not formed by fermentation, but by the condensation of two pyruvate molecules, forming L-acetolactic acid. Propionibacteria are able to decarboxylate L-acetolactic acid, which may explain the observed high rates of CO2 production. 

The acetaldehyde-TPP may then (1) split to yield acetaldehyde, (2) react with itself or a mole of free acetaldehyde to give the acyloin, acetylmethyl-carbinol (AMC), or (3) pass on the activated acetaldehyde molecule to a system which can oxidize it to a substance at the acid level of oxidation. In each case the TPP is made available for another catalytic cycle. The acetaldehyde-TPP intermediate has also been shown to be derived, in special instances, from free acetaldehyde and diacetyl. In some bacteria, the intermediate, derived from 1 mole of pyruvate, donates the acetaldehyde to a second mole of pyruvate to form acetolactic acid. The latter upon decarboxylation yields AMC. These reactions are pre-... 

The mechanism of fusel oil production from carbohydrates follows the typical Embden-Meyerhof-Pamas pathway to pyruvic acid. Pyruvic acid may be reacted with a second pyruvic acid to yield acetolactic acid. Acetolactic acid enters the valine-isoleucine biosynthesis pathway and is converted to a-keto isovaleric acid. The a-keto isovaleric acid may then be reduced to isobutyl alcohol or isobutyric... 

Acetolactic acid, obtained from the condensation of two pyruvate molecules, is the intermediary product in the biosynthetic pathways of valine and leucine (Fig. 5.28). However, 2-acetolactic acid can be decarboxylated in a side reaction into acetoin, the precursor of diacetyl. At a-keto-3-methylbutyric acid, the metabolic pathway branches to form methylpropanal and... 

Yeasts also make use of pyruvic acid to form acetoin, diacetyl and 2,3-butanediol (Figure 2.17). This process begins with the condensation of a pyruvate molecule and active acetaldehyde bound to thiamine pyrophosphate, leading to the formation of cr-acetolactic acid. The oxidative decarboxylation of a-acetolactic acid produces diacetyl. Acetoin is produced by either the non-oxidative decarboxylation of a-acetolactic acid or the reduction of diacetyl. The reduction of acetoin leads to the formation of 2,3-butanediol this last reaction is reversible. 

Strassman et al. (144), on the basis of the equal incorporation of lactate C-2 into valine C-2 and C-3, suggested that valine synthesis was initiated by the condensation of two pyruvate molecules, similar to the known condensation of pyruvate and acetaldehyde to yield acetolactic acid (162). The methyl group of pyruvate was indicated to be the precursor of the valine methyl groups. To explain this required a migration of the methyl group as in the pinacol rearrangement. 

Acetolactic acid, methyl ester, A33 Acetylaranotin, Y21 Acetylchloromalic acid, A1 Achillene, T1 Achillin, T22 Achromycin, Y28 Aconitine, K33 Acoradienes, T29, T5 Acoragermacrone, T22 Acorenols, T29 Acenaphthenes, A35 ... 

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