Yeast carbonyl compounds, using bakers

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... 

Chiral (3-hydroxy esters are versatile synthons in organic synthesis specifically in the preparation of natural products [68-70]. The asymmetrical reduction of carbonyl compounds using baker s yeast has been demonstrated and reviewed [5,71,72]. In the stereoselective reduction of P-keto ester of 4-chloro- and 4-bromo-3-oxobutanoic acid, specifically 4-chloro-3-oxobutanoic acid methyl ester, Sih and Chen [73] demonstrated that the stereoselectivity of yeast-catalyzed reductions may be altered by manipulating the size of ester group using y-chloroacetoacetate as substrate. They also indicated that the e.e. of the alcohol produced depended on the concentration of the substrate used. Nakamura et al. [74] demonstrated the reduction of p-keto ester with baker s yeast and controlled... 

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. ... 

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]. 

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. 

The stereoselective hydrogenation of the carbonyl-activated double bond of bifunctional C1() precursors with baker s yeast was also used in the synthesis of insect pheromones35. The substrates, namely the acetoxy compound and the methyl ester, were prepared from geraniol. 

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... 

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. 

Reaction of lithiodithianes with acyl chlorides, esters or nitriles leads to the formation of 1,2-dicarbonyl compounds in which one of the carbonyl groups is protected as the thioacetal. 476.243.244 Optically active amino ketones of type (69) are inepared via acyl on of dithiane with an oxazoline-prote ed (S)-serine methyl ester (Sch e 41). Optically active (S)-2-alkoxy-l-(l,3-dithian-2-yl)-l-propanenantioselective synthesis of (-)-trachelanthic acid. Enantioselective synthesis of L-glyceraldehyde involves the acylation of a dithiane glycolic acid derivative followed by bakers yeast mediated reduction. ... 

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