Reduction Bakers yeast

So far only two groups have reported details of the use of ionic liquids with wholecell systems (Entries 3 and 4) [31, 32]. In both cases, [BMIM][PF(3] was used in a two-phase system as substrate reservoir and/or for in situ removal of the product formed, thereby increasing the catalyst productivity. Scheme 8.3-1 shows the reduction of ketones with bakers yeast in the [BMIM][PF(3]/water system. 

Crocq et al. (1997) have synthesized trimegestone through Bakers yeast mediated reduction of a ketone (this material is a new progestomimetic molecule for the treatment of postmenopausal diseases). The key step of the multistep synthesis is the chemo-, regio- and almost stereospecific bioreduction of a triketone to the desired alcohol. 

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]. 

Recently bakers yeast reductions in petroleum ether has been explored, Medson, C., Smallridge, A.J. and Trewella, M.A. Tetrahedron Asymmetry, 1997, 8, 1049. 

Enzyme reductions of carbonyl groups have important applications in the synthesis of chiral compounds (as described in Chapter 10). Dehydrogenases are enzymes that catalyse, for example, the reduction of carbonyl groups they require co-factors as their co-substrates. Dehydrogenase-catalysed transformations on a practical scale can be performed with purified enzymes or with whole cells, which avoid the use of added expensive co-factors. Bakers yeast is the whole cell system most often used for the reduction of aldehydes and ketones. Biocatalytic activity can also be used to reduce carbon carbon double bonds. Since the enzymes for this reduction are not commercially available, the majority of these experiments were performed with bakers yeast1 41. 

Asymmetric Reduction of Ketones Using Bakers Yeast... 

Among the strategies developed for the preparation of optically active ester derivatives, the bakers yeast reduction of the corresponding 0-ketoesters is one of the most useful methods. Because of its low cost, ready availability and its utility, bakers yeast can be considered as a relatively simple reagent which is very easy to handle11-31. 

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

BAKERS YEAST REDUCTION OF (Z)-N-CARBOBENZYLOXY-3-KETOPROLINE ETHYL ESTER... 

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]. 

Saccharomyces cerevisiae (Baker Yeast) are micro organisms and are used for the reduction of carbonyl group to hydroxyl group and for reduction of double bond. 

Whole cells of bakers yeast [BMIM][PF6]/buffer (two-phase) Reduction of ketones 32... 

A patented process for the production of green notes applying bakers yeast for in situ reduction of enzymatically produced aldehydes [67, 68] has been called into question regarding the effective production of (Z)-3-hexenol. According to Gatfield s report [69] the isomerisation of (Z)-3-hexenol to (E)-2-hexenal is a very fast process. The latter undergoes facile conversion to hexanol. Beside this, baker s yeast can add activated acetaldehyde to ( )-2-hexenal, forming 4-octen-2,3-diol. 

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... 

Figure 1.18 Bakers yeast reduction of unsaturated aldehydes.

Wipf, B. Kupfer, E. Bertazzl, R. Leuenberger, H. Q. W. Helv. Chim. Acfa 1983, 66, 485. For bakers yeast reduction under aerobic conditions in the absence of sugar, see Ehrter, J. Giovannini, F. Lamatsch, B. Seebach, D. Chimia 1986, 40, 172. 

The two oxidoreductase systems most frequendy used for preparation of chiral synthons include bakers yeast and horse liver alcohol dehydrogenase (HLAD). The use of baker s yeast has been recendy reviewed in great detail (6,163) and therefore will not be covered here. The emphasis here is on dehydrogenase-catalyzed oxidation and reduction of alcohols, ketones, and keto acid, oxidations at unsaturated carbon, and Bayer-Villiger oxidations. 

J. Buendia, and D. Prat, Synthesis of trimegestone the first industrial application of bakers yeast mediated reduction of a ketone, Org. Proc. Res. Dev. 1997, 3, 2-13. 

K Nakamura, S Kondo, Y Kawai, A Ohno. Reduction by bakers yeast in benzene. Tetrahedron Lett 7075-7078, 1991. 

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