Bakers’ yeast yield

Bakers Yeast Production. Bakers yeast is grown aerobicaHy in fed-batch fermentors under conditions of carbohydrate limitation. This maximizes the yield of yeast biomass and minimizes the production of ethanol. Yeasts grown under these conditions have exceUent dough leavening capabHity and perform much better in the bakery than yeast grown under anaerobic conditions. 

Optically pure a, . (R)-3-hydroxybutanoates can be obtained by alcoholysis of poly-(R)-3-hydroxybutanoate, a fermentation product of fructose by Alcaligones eutrophus.4 (S)-Ethyl 3-hydroxybutanoate in 84-87% ee can be synthesized in 57-67% yield on a decagram-scale by an Organic Syntheses procedure6 using bakers yeast reduction of ethyl 3-oxobutanoate with the aid of sucrose.7 In order to obtain enantioselectivity as high as 95-97% ee, the substrate concentration should be kept below 1 g/L.6... 

It is well known that bakers yeast is capable of reducing a wide range of ketones to optically active secondary alcohols. A recent example involves the preparation of the (R)-alcohol (7) (97 % ee) (a key intermediate to ( norephedrine) from the corresponding ketone in 79 % yield1281. Other less well-known organisms are capable of performing similar tasks for instance, reduction of 5-oxohexanoic acid with Yamadazyma farinosa furnishes (R)-5-hydroxyhexanoic acid in 98 % yield and 97 % ee[29]. 

Very few enzyme-catalysed reactions involving the reduction of alkenes have achieved any degree of recognition in synthetic organic chemistry. Indeed the only transformation of note involves the reduction of a, (3-unsaturated aldehydes and ketones. For example, bakers yeast reduction of (Z)-2-bromo-3-phenylprop-2-enal yields (S)-2-bromo-3-phenylpropanol in practically quantitative yield (99 % ee) when a resin is employed to control substrate concen-tration[50]. Similarly (Z)-3-bromo-4-phenylbut-3-en-2-one yields 2(5), 3(,S)-3-bromo-4-phenylbutan-2-ol (80% yield, >95% ee)[51]. Carbon-carbon double bond reductases can be isolated one such enzyme from bakers yeast catalyses the reduction of enones of the type Ar—CH = C(CH3)—COCH3 to the corresponding (S)-ketones in almost quantitative yields and very high enantiomeric excesses[52]. 

Microbial deoxygenation of benzo[f]cinnolin-5-ium oxide with Bakers yeast-NaOH in EtOH/water at reflux yielded 90% of benzo[f]cinnoline <1997TL845>. The same deoxygenation has been achieved in a similar yield via heating in EtOH with NaOEt at 160°C in a sealed tube <2004JOC7720>. 

A fermentation procedure has been described237,238 for large-scale production of the latter sugar nucleotide. Bakers yeast transforms guanosine 5 -phosphate into the D-mannosyl pyrophosphate ester in 45% yield when a mixture with D-glucose, potassium phosphate, and magnesium sulfate is incubated. 

Asymmetric reduction of a,/l-unsaturated aldehydes with transition metal catalysts has not yet proven ready for widespread industrial application. One area, namely the chiral reduction of enals to yield chiral alcohols using bakers yeast has been... 

Reduction of a cyclobutanone with baker s yeast yielded the diastereomeric alcohols 5 which could be separated by column chromatography.163 The optical purity was reported to be ca. 90%. Stereoselective reductions using isolated enzymes or complete organisms have also been reported for 6.82-276 278... 

Hexahydro-117/-pyrido[2,l-b]quinazoline alkaloid was obtained in 70% yield when l-(2 -nitrobenzyl)-2-cyanopiperidine was reduced with Zn in acidified EtOH at 78 °C (99SL1383). 6,7,8,9-Tetrahydro-1 l//-pyrido[2, l-b]quinazolin-l 1-ones (426) were synthesized by azidoreductive cyclization of /V-(2-azidobenzoyl)-2-piperidones 425 using TMSCl-Nal and bakers yeast (01JOC997). 

Sarcosine (1 g.) and dry, powdered D-glucose (10 g.) in N,N-dimethylformamide (30 ml.) were heated at 100°. Dissolution was complete in ten minutes, and the mixture was heated for a further 30 minutes. The yellow sirup remaining after removal of the solvent under diminished pressure was freed of D-glucose with bakers yeast. After 5 days, paper-chromatographic examination showed that no D-glucose or d-mannose remained. The solution was decolorized and the water was removed by evaporation under diminished pressure. Purification from methanol and ether gave an amorphous powder (2 g., 70% yield), [a]D — 49 1° (in water). 

A Cyclic (3-Hydroxy Ester as a Building Block for Sporogen-AOl. Reduction of ethyl 2-oxocyclohexane-l-carboxylate with baker s yeast was first studied by Ridley in 1976 (12). Reduction of an analogous (3-keto ester 21 with baker s yeast yielded ethyl (lR,2S)-5,5-ethylenedioxy-2-hydroxycyclohexane-l-carboxylate (22) of 98.4% e.e. (23). 

The next phase in the development of advanced fermentation ethanol processes concerns the conversion to ethanol of all the pentose and hexose sugars released on hydrolysis of lignocellulosics. Traditional bakers yeast strains promote fermentation of hexoses at high yields, but over long periods of time, and they do not ferment the pentoses. Although some yeasts use both hexose and pentose sugars as sources of carbon and energy and ferment hexoses and xylose, they do not ferment arabinose and the other pentoses. The overall stoichiometry of hemicellulose hydrolysis and pentose fermentation is... 

As previously mentioned and in the earlier discussion of fermentation methanol, bacteria of the genus Zymomonas such as Z. mobilis are known to convert hexoses to ethanol at high yields and short residence times. These bacteria are facultative anaerobes that have fermentative capacity and convert only glucose, fructose, and sucrose to equimolar quantities of ethanol and CO2 the pentoses are not converted. The Entner-Doudoroff pathway is utilized instead of the Embden-Meyerhof pathway, and a net yield of 1 mol of ATP is generated, not 2 mol as in bakers yeast. But pyruvate is the same key intermediate. In Z. mobilis, it is decarboxylated by pyruvate decarboxylase to yield acetaldehyde which is then reduced to ethanol by alcohol dehydrogenase. 

A different protocol for the asymmetric synthesis of 3-hydroxy-2-(4-methoxyphenyl)-2,3-dihydro-l,5-benzothiazepin-4(5//)-one has been disclosed <05H147>. The novelty in this procedure resides in the use of bakers yeast to reduce P-arylthio-a-keto ester precursors to the corresponding hydroxy esters in fair yields and reasonable stereoselectivities (diastereomer ratios and ee s). 

The most widely used whole cell biocatalyst is bakers yeast. Since it has many different kinds of enzymes, many kinds of substrate can thus be reduced, and various types of the reactions are expected. For example, p-keto esters, aromatic, aliphatic, cyclic and acyclic ketones can be reduced with high yield[1- 37 391. Therefore, it is a versatile all-round reagent. However, since bakers yeast contains many kinds of dehydrogenases, some of them may be S selective, while others are R selective, so that the enantioselectivities can be low to high depending on the substrate structure. Further degradation of the product may also be a problem, again associated with the fact that there are many kinds of enzymes in the cell. 

For example, the effect of cultivation time and different carbon sources on the enantioselectivity of the reduction of sulcatone by some anaerobic bacteria has been investigated [8 if Another example is the investigation on the effect of the medium concentrations for cultivation of Geotrichum candidum IFO 4597 on the enantioselectivity of the reduction of acetophenone derivatives. The yield of l -alcohol (the minor enantiomer) increased with the medium concentration therefore, the medium concentration was kept low, optimally to produce the S-enantiomer[82]. The effect of the aeration during cultivation on the enantioselectivity of bakers yeast production of 3-hydroxyesters has also been reported 86 Inducers such as a substrate analog may also induce the desired enzyme to improve the enantioselectivity. 

Bakers yeast catalyzes the reduction of azides and nitro compounds to amines128 2911. For example, it catalyzes chemoselective reduction of azidoarenes to arenamines as shown in Fig. 15-50[286, 287). Excellent yields are obtained for various aromatic compounds on reaction at room temperature. Aromatic nitro compounds... 

On the other hand, 6-oxobicyclo[3.2.0]hept-2-ene is transformed by bakers yeast to the endo- and em-alcohols in 38.5% and 18% yield respectively, and in reasonable optical purity (>90%)268. 

It has been found that aldehydes of the cinnamaldehyde type undergo an interesting biotransformation in the medium of growing baker s yeast yielding optically active methyl diols (e.g., 58, 59). 

---