With Baker s yeast

Even more highly selective ketone reductions are earned out with baker s yeast [61, 62] (equations 50 and 51) Chiral dihydronicotinamides give carbonyl reductions of high enantioselectivity [63] (equation 52), and a crown ether containing a chiral 1,4-dihydropyridine moiety is also effective [64] (equation 52). 

Asymmetric synthesis of spiroketahc pheromones Is also reported. In which the asymmetric redncdon of carbonyl group Is carried out with baker s yeast fScheme 4.22. ... 

Figure 8.24 Reduction of ketone with baker s yeast in the presence of hydrophobic polymer XAD [16b].

The reduction of hydroxy or acetoxy ketones by baker s yeast shows an interesting stereoselectivity. For the reduction of acetylbenzofuran derivatives with baker s yeast, the methyl ketones afforded (S)-alcohol in 20-68% ee. The hydroxyl derivatives afforded (S)-alcohol in 87-93% ee, and the acetoxy derivatives gave (R)-alcohols in 84-91% ee (Figure 8.33) [24bj. 

COOH or NHCOCH3, for example, 2-phenyl-l-butene. Enantioselective reduction of certain alkenes has also been achieved by reducing with baker s yeast. Hydrogenation with Ni2B on borohydride exchange resin (BER) has also been... 

Asymmetric synthesis of spiroketalic pheromones is also reported, in which the asymmetric reduction of carbonyl group is carried out with baker s yeast (Scheme 4.22).160... 

A short enantioselective synthesis of (-)-(R,R)-pyrenophorin, a naturally occurring anti-fun-gal 16-membered macrolide dilactone, is prepared from (S)-5-nitropentan-2-ol via the Michael addition and Nef reaction (Scheme 4.23).162 The choice of base is important to get the E-alkene in the Michael addition, for other bases give a mixture of E and Z-alkenes. The requisite chiral (S)-5-nitropentan-2-ol is prepared by enantioselective reduction of 5-nitropentan-2-one with baker s yeast.163... 

The reduction of nitro ketones with baker s yeast is a good method for the preparation of chiral nitro alcohols.89 The reduction of 5-nitro-2-pentanone with baker s yeast gives the corresponding (5)-alcohol, which is an important chiral building block. Various chiral natural products are prepared from it. In Scheme 7.16, the synthesis of the pheromone of Andrena haemorrhoa is described, where the acylation of the chiral nitro alcohol followed by radical denitration is involved as key steps.89a... 

Bertau, M. and Burli, M. (2000) Enantioselective microbial reduction with baker s yeast on an industrial scale. Chimia, 54 (9), 503-507. 

Li, Y.-N., Shi, X.-A., Zong, M.-H. et al. (2007) Asymmetric reduction of 2-octanone in water/organic solvent biphasic system with baker s yeast FD-12. Enzyme and Microbial Technology, 40, 1305-1311. 

Scheme 65 summarizes Mori s synthesis of 44 [97]. Reduction of keto ester A with baker s yeast gave hydroxy ester B of about 98% ee. Methylation of the dianion derived from B diastereoselectively gave C, which was converted to 44. This process enabled the preparation of about 10 g of (lS,5R)-44. 

A procedure that is described by Tollens and Eisner4 is probably suitable for materials less pure than fresh dahlia juices. The juice is expressed in the presence of calcium carbonate, fermented at 25° with baker s yeast, defecated with lead acetate and filtered. After removal of the excess lead with hydrogen sulfide, the filtrate is frozen and thawed to cause the separation of inulin. 

Hydroxy esters have been obtained successfully with baker s yeast (Sac-charomyces cerevisidae), and this has shown a wide scope of application. The facial selectivity in the reduction of both isolated ketones and //-keto esters can be reliably determined by using Prelog s rule,8 which predicts that the hydrogen addition by the yeast will occur from the front face (Scheme 8-2). Anti-Prelog microbial reduction of a-ketones with Geotrichum sp. 38 (G38) has been introduced by Gu et al.9... 

Enzyme reduction with Baker s yeast and enantioselective rule... 

Hydroxy ketones and hydroxy-a,/3-unsaturated ketones in the steroids such as estrone and testosterone, respectively, can be reduced to diols biochemically. Estrone acetate gave 68% yield of a-estradiol on incubation with baker s yeast at room temperature after five days [909]. Testosterone was reduced by bacteria to the saturated hydroxy ketones, etiocholan-17-ol-3-one and androstan-17-ol-3-one, and further to the diols, ep/-etiocholane-3,17-diol and the epimeric isoandrostane-3,17-diol, both in low yields [329]. 

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]. 

Shaking of rac-3,4-dihydro-6-methyl-2-(l-oxopropyl)-2/f-pyran with baker s yeast resulted in initial formation of racemic 6-hydroxy-2,7-nonanedione and then by kinetic resolution/ diastereoselective reduction in the production of (67 ,7S)-6,7-dihydroxy-2-nonanone (2) where both relative and absolute configuration had to be determined (see p 470)134. 

Highly enantioselective reduction of ethyl 6-benzyloxy-3,5-dioxohexanoate by ADH of Acinetohacter calcoaceticus has been reported (97 to >99% ee) [6]. Regi-oselectivity was not encountered, however, as was the case in the reduction of a variety of 3,5-dioxohexanoates A with baker s yeast [7]. The application of isolated enzymes in an anticipated regio- and enantioselective reduction of diketo esters A seemed most promising to us. 

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... 

Figure 10.19 Enantioselective ketone reduction with baker s yeast in an ionic liquid...

The RQ control, where the sugar-feeding rate is controlled so as to maintain the RQ value at approximately 1.0, is the distinct control method in aerobic fed-batch cultivation such as with baker s yeast production. By keeping the RQ at 1.0 during the fed-batch operation, cell production with a high yield will be achieved. 

GDP-Man From Glc and GMP with Baker s yeast From Man-l-P and GTP with GDP-Man pyrophosphorylase... 

During the pine saw-fly pheromone synthesis based on thiophilic addition it was shown that high enantio- and diastereoselectivity were observed in the reduction of p-ketodithioesters with baker s yeast, affording new and useful chiral synthons [346]. 

Methyl-5-hepten-2-one is a valuable precursor for microbial epoxidations and hence the production of chiral ethers with high optical purities. The biotransformation of 6-methyl-5-hepten-2-one (33) by Botryodiplodia malorum CBS 13450 to (/ )-sulcatol (84) was described [61], which is then epoxidised to the (55)-epoxide (85) and opened intramolecularly to cis-(2R,5R)-2-(2 -hydroxyisopropyl)-5-methyltetra-hydrofuran (86) and c/s-(35,67 )-3-hydroxy-2,2,6-trimethyltetrahydropyran (87). Reduction of 6-methyl-5-hepten-2-one (33) with baker s yeast to (5)-sulcatol (88) which was used as substrate for Kloeckera corticis... 

Advances in the Synthesis of Chiral Fluorinated Compounds with Baker s Yeast ... 

An important step in the asymmetric synthesis of the angiotensin-converting enzyme inhibitor, benazepril HC1 132, was the reduction of the ketoester 128 (obtained from 127 by condensation with diethyl oxalate) with baker s yeast to give the chiral cr-hydroxy ester 129 in high yield and ee (Scheme 17). Direct formation of the 1//-1-benzazepin-2-one 131 from 129 proceeded in 42% yield (without racemization at C-3) or in 74% yield in two steps via 130, again with no racemization <2003TA2239>. 

K Nakamura, Y Kawai, S Oka, A Ohno. A new method for stereochemical control of microbial reduction. Reduction of (3-keto esters with baker s yeast immobilized by magnesium alginate. Tetrahedron Lett 2245-2246, 1989. 

K Nakamura, Y Kawai, T Miyai, A Ohno. Stereochemical control in diastereoselec-tive reduction with baker s yeast. Tetrahedron Lett 3631-3632, 1990. 

Ethanol production depends not only on the sugar yield, but also on the fermentability of the solution. To investigate the fermentability of the pretreated com stover, fermentations were performed with baker s yeast. Baker s yeast has often been proposed as the best organism for the fermentation of lignocellulosic hydrolysates (28,29) and has the advantages that it is quite robust and was found to be less sensitive to inhibitors than cultivated yeast (30,31). 

Ethanol Yield (%) of Theoretical and Achieved Ethanol Concentration (g/L) After 24 h of Fermentation at 30°C with Baker s Yeast from 30 g/L of Glucose Solution... 

Although the reduction of pyridyl A-oxides with baker s yeast has been reported, the reaction has not been readily employed due to the low yields and long reaction times. Baik etal. found that addition of NaOH greatly increased the efficiency of the reaction, thus producing the desired products in high yield (Equations 12 and 13) <1997TL845>. Several methods are available for the reduction of heteroaromatic A-oxides <2001ARK242>. 

The enzymatic reduction of a thiocarbonyl compound has been investigated [159] for the first time, in order to provide a new route for enan-tiopure thiols, molecules which are currently needed for asymmetric synthesis. Reaction of easily available /1-thioxoesters with baker s yeast under classical conditions did furnish the expected thiols, but with lower enantiomeric purity and moderate conversion rate, due to the competitive hydrolysis of the thioxo group into a carbonyl leading to an alcohol. However, conditions (ethyl acrylate, dry yeast) were found to improve the production of (S)-ethyl 3-mercaptobutanoate. Cyclic thioxo esters led to high stereoselectivity of cis (1S,2S) products, but with moderate chemical yields. 

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