Bakers yeast-catalyzed reaction

One of the most usefijl biocatalysts is the baker s yeast. It has been widely used to synthesize chiral intermediates. For example, baker s yeast reduction of diketones proceeds highly regio- and enantioselectively with ahphatic diketones, 2,2-disubstituted cycloalkanediones and spiro diones, producing enantiomericaUy enriched hydroxyketones (Fig. 10.7). Starting from a chiral hydroxyketone, many terpenes have been enantioselectively synthesized by Mori et at, as shown in Fig. 10.7(a).  

The enantioselectivity of the baker s yeast reduction is excellent for the examples in Fig. 10.7. However, it is not always high, because there are many enzymes existing in the whole cell and some of them are S-selective and others are J -selective. For example, in the reduction of j8-keto esters, the enantioselectivity is low and (S)-alcohols are produced when the ester 

---

Kumar A, Maurya RA (2007) Bakers yeast catalyzed synthesis of polyhydroquinoline derivatives via an unsymmetrical Hantzsch reaction. Tetrahedron Lett 48 3887-3890... 

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... 

As a rule, saturated alcohols are formed by treatment of a./i-unsaturated aldehydes with baker s yeast. It is remarkable to note that the corresponding saturated carboxylic acids were obtained in the yeast-catalyzed reaction of these sulfur-containing a,/f-unsaturated aldehydes. This type of biotransformation has so far only been observed with the fungus Geotrichum candidum21. 

Rao and colleagues [80] reported the first example of baker s yeast-catalyzed Diels-Alder reaction. Reactions of cyclopentadiene (1) with dienophiles 119 and 120 (Scheme 4.21) in the presence of baker s yeast at pH 7.2 afford prevalently the exo adduct with the exception of crotonic acid 120a. 

An IL solvent system is applicable to not only lipase but also other enzymes, though examples are still limited for hpase-catalyzed reaction in a pure IL solvent. But several types of enzymatic reaction or microhe-mediated reaction have been reported in a mixed solvent of IL with water. Howarth reported Baker s yeast reduction of a ketone in a mixed solvent of [hmim] [PFg] with water (10 1) (Fig. 16). Enhanced enantioselectivity was obtained compared to the reaction in a buffer solution, while the chemical yield dropped. 

Baker s yeast catalyzed the regioselective cycloaddition of stable aromatic nitrile oxides ArCNO [Ar = 2,6-C12C6H3, 2,4,6-Me3C6H2, 2,4,6-(MeO)3C6H2] to ethyl cinnamate, ethyl 3-(p-tolyl)acrylate, and tert-butyl cinnamates (218). Reactions of dichloro- and trimethoxybenzonitrile oxides with all three esters proceeded regio- and stereoselectively to form exclusively alkyl tran.v -3,5-diary 1 -... 

Kometani et al. [71] reported that baker s yeast catalyzed the asymmetric reduction of acetol to (i )-1,2-propanediol with ethanol as the energy source. The enzyme involved in the reaction was an NADH-dependent reductase, and NADH required for the reduction was supplied by ethanol oxidizing enzyme(s) in the yeast. When washed cells of baker s yeast were incubated with 10 mg ml of acetol in an ethanol solution with aeration, (k)-1,2-propanediol was formed almost stoichiometrically with an optical purity of 98.2% e. e. 

Although reductases play an important role in the in vivo synthesis of many chemicals (see flavour example in Fig. 7.11), little attention has been paid to this type of biocatalyst. In most cases whole microbial or plant cells are used to perform a bioreductive reaction due to the requirement for (expensive) cofactors. Typical examples include the reduction of certain double bonds in terpenes by plant cells [27,41], the reduction of Massoi lactone to R(+)-8-decalactone by Basidiomycetes and S. cerevisiae [28], and the baker s yeast-catalyzed reduction of ketones to (chiral) alcohols [42]. 

Scheme 2.199 Synthesis of (-)-ephedrine via baker s yeast catalyzed acyloin reaction and acyloin formation catalyzed by pyruvate decarboxylase...

The transketolase enzyme of Racker el obtained in crystalline form from baker s yeast, catalyzes the cleavage of ribulose-5-phosphate, with the formation of D-glyceraldehyde-3-phosphate upon the addition of an acceptor aldehyde, such as ribose-5-phosphate or glycolaldehyde. The reaction of hydroxypyruvate with D-glyceraldehyde-3-phosphate as acceptor aldehyde leads to the decarboxylation of the hydroxypyruvate with the formation of ribulose-5-phosphate. The transketolase enzyme was demonstrated to have a requirement for thiamine pyrophosphate. ... 

The presence of a specific ribokinase has been reported in extracts of bakers yeast ° and in extracts of certain strains of E. coli. The reaction catalyzed by these systems was ... 

Regio- and enantioselective reduction of diketones have been conducted successfully by biocafalysis. Examples for the reduction of diketones to hydroxyl ketones and diols are shown in Figure 11.11. Figure 11.11a shows the preparation of a key intermediafe for the synthesis of terpenoids by a baker s yeast-catalyzed reduction of a o-cyclohexanedione. DMSO (10%) was used to solubilize the substrate [67]. Figure 11.11b shows the reduction of 3,5-dioxo-6-(benzyloxy)hexanoic acid ethyl ester by Acinetobacter sp. SC 13874 to the corresponding si/n-(3R,5S)-diol, potential intermediates for die s)mthesis of HMG-CoA reducfase inhibitors, in 99.4% ee with 52-74% de depending on substrate concentrations (74% de in 2g/l and 52% de in lOg/1) [66]. After the reaction, XAD-16 resin was added to facilitate the recovery process by adsorbing the product. 

The reduction of different y-chloroacetoacetates 58 and 59 (Figure 21.18) has been studied quite often and in more detail, and its stereochemical course (to 5ueld products 60 and 61, respectively) can be altered by changing the size of the ester moiety [17, 248, 255, 256]. The addition of a nonpolar resin to the reaction mixture also increased yields and selectivity [257], Recently, enantioselective keto ester reductions in water have been accomplished either by baker s yeast or by ruthenium-catalyzed reactions interestingly enough, the highest ee values have been obtained using S. cerevisiae [258]. In addition, a metabolic in vivo study has been performed. These data revealed that under aerobic conditions the reduction occurs preferentially in the mitochondrial matrix, while under anaerobic conditions the bioreduction occurs in the cytosol [259]. 

This enzyme [EC 4.2.99.10], also referred to as O-acetyl-homoserine sulfhydrylase, catalyzes the reaction of O-acetylhomoserine with methanethiol to generate methionine and acetate. The enzyme can also act on other thiols or H2S, producing homocysteine or thioethers. The enzyme isolated from baker s yeast will also catalyze the reaction exhibited by O-acetylserine (thiol)-lyase [EC 4.2.99.8], albeit more slowly. 

Usually a large number of other reactions will occur simultaneously, some of them being beneficial for the coenzyme regeneration, whereas others lead to undesired byproducts. Also, the substrate and prodnct of the main reaction may get involved in undesirable side-reactions. Therefore, whole cell reactions may be cheaper and simpler to carry out than reactions using isolated enzymes, bnt they are less easily controlled, less reproducible and yield more waste. The most widely stndied class of reactions nsing whole cells are redactions catalyzed by baker s yeast, which is cheap and widely available (Sybesma et al 1998). 

Organic chemists, who are not generally keen on growing cultures, began using baker s yeast which is readily available and cheap, using it like a common shelf reagent in reactions very similar to the natural transformations that it catalyzes.Most of the current applications of baker s yeast involve stereospecific... 

Several synthetic examples that successfully exploit TK for biocatalytic conversions have been reported. For example, the total synthesis of the beetle pheromone (+)-exo-brevicomin utilizes TK from Baker s yeast as the sole chiral reagent. Starting with racemic 2-hydroxybutanol, the ability of TK to effect kinetic resolution of substrates was exploited (Scheme 5.56). The smooth reaction of 2-hydroxybutanol with HPA was catalyzed by TK at pH 7.5 to yield the enantioenriched ketone in 90% yield. This intermediate was chemically converted into (+)-exo-brevicomin.101... 

Capillary gas chromatographic determination of optical purities, investigation of the conversion of potential precursors, and characterization of enzymes catalyzing these reactions were applied to study the biogenesis of chiral volatiles in plants and microorganisms. Major pineapple constituents are present as mixtures of enantiomers. Reductions, chain elongation, and hydration were shown to be involved in the biosynthesis of hydroxy acid esters and lactones. Reduction of methyl ketones and subsequent enantioselective metabolization by Penicillium citrinum were studied as model reactions to rationalize ratios of enantiomers of secondary alcohols in natural systems. The formation of optically pure enantiomers of aliphatic secondary alcohols and hydroxy acid esters using oxidoreductases from baker s yeast was demonstrated. 

---