Carbonyl compounds yeast

Table 10.1 Reduction of carbonyl compounds mediated by bakers yeast (results according to the literature).

Table IV. Carbonyl Compounds in Yeast Bread (mg/100 g dry weight) (57)...

Enzymes are natural biocatalysts that are becoming increasingly popular tools in synthetic organic chemistry [1]. The major areas of exploration have involved the use of hydrolases, particularly esterases and lipases [2]. These enzymes are readily available, robust and inexpensive. The second most popular area of investigation has been the reduction of carbonyl compounds to chiral secondary alcohols using either dehydrogenases (with co-factors) or a whole-cell system such as bakers yeast [3]. 

In addition to 9—12, several useful chiral carbonyl compounds have been obtained from the diols obtained by yeast treatment of the corresponding a-hydroxyketones. As a part of a study (2) on the substrate specificity of the multienzymic conversion shown in Eq. 2, a serie of racemic a-hydroxyketones has been prepared and submitted to the yeast treatment. The reduction process is stereospecific, but depending upon... 

The bioreduction of carbonyl compounds with reductases has been exploited for many years, especially in the case of ketones, with baker s yeast Saccharomyces cerevisiae) being the most popular biocatalyst [45]. For instance, yeast treatment of 3-chloropropiophenone affords the expected (lS)-3-chloro-l-phenylpropan-l-ol, which was treated with trifluorocresol in tertrahydrofuran in the presence of tri-phenylphosphine and diethyl azodicarboxylate at room temperature to give (3R)-l-chloro-3-phenyl-3-[4-(trifluoromethyl)phenoxy]propane and the later reaction with methylamine leads to (R)-fluoxetine that is an important serotonin uptake inhibitor (Scheme 10.19) [46]. 

Related examples are, for example, found in the area of catalyzed Diels-Alder reactions228. On reduction of carbonyl compounds by baker s yeast, in many cases hydrogen transfer occurs at the Re-face of the prostereogenic ketone 31 to yield alcohol 32 (Prelog s rule77). 

Baker s yeast reduction of organic compounds, especially carbonyl compounds, is an extremely useful method of obtaining chiral products255-257. Recently, much effort has been expended to improve the ee obtained in this process. In one very useful example, l-acetoxy-2-alkanones have been reduced enantioselectively into (5 )-l-acetoxy-2-alkanols in 60-90% yields and with 95-99% ee258. The reaction readily occurs in a variety of solvents, both aqueous and nonaqueous. The reduction is fairly selective and so may be brought about in the presence of a-amide, ether, ester and other acid functional groups, in reasonable yields and with excellent ee (equation 65)259 -261. Thus, in the synthesis of the C-13 side chain of taxol, the key step was the reduction of a w-ketoester to the corresponding alcohol in 72% overall yield (equation 66)262. 

Chiral (l-hydroxy esters are versatile synthons in organic synthesis, specifically in the preparation of natural products [62-64], The asymmetric reduction of carbonyl compounds using Baker s yeast has been demonstrated and reviewed... 

An example of removal of carbonyl compounds is dried Chinese egg white, which used to be the best product available, because it had been allowed to ferment naturally for 48-72 h, the main carbonyl compound, glucose, being removed in this way. However, fermentation may allow dangerous bacteria to multiply. Yeast fermentation is therefore preferred, but gives yeasty flavours. 

Lactones are another group of carbonyl compounds formed by yeast during alcoholic fermentation. Concentrations are expecially high during oxidative mat-... 

Formation of 3-MHA occurs thorough a more complex mechanism, that involves first liberation of 3-MH from the cysteinyl-conjugate precursor, followed by yeast-driven esterification with acetic acid (Fig 8D.10). The formation of 3-MHA from 3-MH occurs through the same pathway leading to the formation of acetate esters, since over expression of the alcohol acetyltransferase gene ATFl increased formation and overexpression of esterase gene lAHl decreased formation (Swiegers et al. 2006). 3-MH can also form chemically by reaction between H2S produced by the yeast and carbonyl compounds present in the must, such as 2-hexenal. This pathway only accounts for 10% of the 3-MH typically formed in fermentation (Schneider et al. 2006). 

With regards to carbonyl compounds, acetaldehyde is the predominant aldehyde formed during fermentation most aldehydes produced, however, are formed independent of direct yeast action (29,30). Delteil and Jarry (57) found significant strain-specific production differences- , cerevisiae strain K1 producing 128 mg/L and S. cerevisiae strain D47 producing 105 mg/L Ough and Amerine (52) report average acetaldehyde concentrations in wines on the order of 54 mg/L. 

When chemical transformations were performed by whole cells, such as the reduction of carbonyl compounds by baker s yeast. 

Two key chiral building blocks used in the total synthesis of a-tocopherol were prepared via microbial reduction of unsaturated carbonyl compounds with baker s yeast and with Geotrichum candidum Similarly, a key intermediate in the total synthesis of optically active natural carotenoids was prepared by microbial reduction of oxoisophorone with baker s yeast. An alternative approach to the synthesis of a-tocopherol employs a chiral building block that was obtained by baker s yeast reduction of 2-methyl-5-phenylpentadienal. ... 

Most known thiamin diphosphate-dependent reactions (Table 14-2) can be derived from the five halfreactions, a through e, shown in Fig. 14-3. Each half-reaction is an a cleavage which leads to a thiamin- bound enamine (center. Fig. 14-3) The decarboxylation of an a-oxo acid to an aldehyde is represented by step h followed by fl in reverse. The most studied enzyme catalyzing a reaction of this type is yeast pyruvate decarboxylase, an enzyme essential to alcoholic fermentation (Fig. 10-3). There are two 250-kDa isoenzyme forms, one an tetramer and one with an (aP)2 quaternary structure. The isolation of a-hydroxyethylthiamin diphosphate from reaction mixtures of this enzyme with pyruvate provided important verification of the mechanisms of Eqs. 14-14,14-15. Other decarboxylases produce aldehydes in specialized metabolic pathways indolepyruvate decarboxylase in the biosynthesis of the plant hormone indole-3-acetate and ben-zoylformate decarboxylase in the mandelate pathway of bacterial metabolism (Chapter 25). Formation of a-ketols from a-oxo acids also starts with step h of Fig. 14-3 but is followed by condensation with another carbonyl compound in step c, in reverse. An example is decarboxylation of pyruvate and condensation of the resulting active acetaldehyde with a second pyruvate molecule to give l -a-acetolactate, a reaction catalyzed by acetohydroxy acid synthase (acetolactate synthase). Acetolactate is the precursor to valine and leucine. A similar ketol condensation, which is catalyzed by the same S5mthase, is... 

Bertrand, 1994 Allen, 1995) decanal and ( )-2-nonenal, on the other hand, are associated with sawdust or plank odour (Chatonnet and Dubourdieu, 1996 1998). The principal carbonyl compound formed in MLF is 2,3-butanedione (diacetyl), whose level can improve, or affect, the wine with its butter-like or fat note (Davis et al., 1985). Diacetyl and 3-hydroxy-2-butanone (acetoin, the reduced form of diacetyl) are produced by pyruvate metabolism of yeasts and lactic bacteria, and their levels may increase two or three fold with MLF depending on the lactic bacteria strain involved (Davis et al., 1985 Martineau and Henick-Kling, 1995 Radler, 1962 Fornachon and Lloyd, 1965 Rankine et al., 1969 Mascarenhas, 1984). For diacetyl in wine sensory thresholds ranging from 0.2mg/L (in Cbardonnay) to 0.9mg/L (Pinot noir), and 2.8 mg/L (Cabernet Sauvignon wine), are reported (Martineau et al., 1995). 

The hydrophobic resin has also been used for the purpose of controlling selectivity 123 1241. Enantioselectivity, chemoselectivity and space-time yields of the yeast reduction of a,p-unsaturated carbonyl compounds were impressively enhanced. The distribution of substrates and products between the resin and the water phase showed that the improved selectivity could be attributed to the control of substrate concentration. 

The reported applications of esterolytic applications used esterases (21%), lipases (63%), and proteases (16%). The most often and widely used biocatalysts were pig liver esterase, pig pancreatic lipase and lipase from Candida cylindracea. Among the proteases, a-chymotryp-sin, papain, penicillin aminoacylase and subtilisin were used most frequently. In the case of stereospecific reductions of carbonyl compounds the use of whole cells of baker s yeast (Sac-charomyces cerevisiae) [75-77] accounted for 54% of the total dehydrogenase applications. The dominance of just very few biocatalytic systems, seems to indicate the direction in which... 

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