YEAST REDUCTION, of ethyl acetoacetate

YEAST REDUCTION OF ETHYL ACETOACETATE (S)-(+)-ETHYL 3-HYDR0XYBUTAN0ATE (Butanoic acid, 3-hydroxy-, ethyl ester, ( ))... 

YEAST REDUCTION OF ETHYL ACETOACETATE (S)-(+)-ETHYL 3-HYDROXYBUTANOATE... 

The 3(S)-hydroxybutanoate 141 obtained by bakers yeast reduction of ethyl acetoacetate was the starting material providing the required chirality at C37 (Scheme 18). Stereoselective alkylation, hydroxy group protection, and aldehyde formation at C35 gave the anti-product 142. Aldol condensation with vinylbor-... 

Ethyl (S)-3-hydroxybutanoate has been obtained by yeast reduction of ethyl acetoacetate in 87 ee and converted into (S)-( + )-sulcatol, 6-methyl-5-hepten-2-ol... 

In Experiment 28A, the yeast reduction of ethyl acetoacetate forms a product that is predominantly the (S)-enantiomer of ethyl 3-hydroxybutanoate. In this part of the experiment, we will use NMR to determine the percentages of each of the enantiomers in the product. The 300 MHz proton NMR spectrum of racemic ethyl 3-hydroxybutanoate is shown in Figure 1. The expansions of fhe individual patterns from Figure 1 are shown in Figure 2. The methyl protons (HJ appear as a doublet at 1.23 ppm, and the methyl protons (H, ) appear as a triplet at 1.28 ppm. The methylene protons (H and H ) are diastereotopic (nonequivalent) and appear at 2.40 and 2.49 ppm (each a doublet of doublefs). The hydroxyl group appears at about 3.1 ppm. The quartet at 4.17 ppm results from the methylene protons (HJ split by the protons (Hjj).The methane proton (H ) is buried under the quartet at about 4.2 ppm. 

S -tridecylacetate and 2S-tridec-1OE -enylacetate, the sex ph eromones of the fruit fly Drosophilia mulleri) and the Hessian fly Mayetiola destructor) have been synthesized using ethyl-SS-hydroxybutanoate, a product from the enzymatic reduction of ethyl acetoacetate by the soil yeast strain 80-l .l58... 

Preparaton of the Enantiomers of Ethyl 3-Hydroxybutanoate. Reduction of ethyl acetoacetate with yeast yields ethyl (S)-3-hydroxybutanoate (15) as shown in Figure 4 (12-14). Purification of crude 15 as its crystalline 3,5-dinitrobenzoate gives (S)-15 of 100% e.e. (14,15). 

Where there is a chiral centre adjacent to the ketone it may also influence the stereochemistry of the reduction. Thus the reduction of ethyl acetoacetate (10.8) by yeast has the stereochemical result shown in 10.9. 

An optically active reagent 32 for the left hand fragment can be made by asymmetric reduction of ethyl acetoacetate with ordinary baker s yeast (see chapter 29), protection of the OH group as a mixed acetal 31, reduction of the ester and conversion of the new OH group into an iodide 32. 

In 1981 we started our works to employ ethyl (S)-3-hydroxybutanoate (B, Figure 4.35) as a chiral and nonracemic building block in pheromone synthesis. Reduction of ethyl acetoacetate (A) with fermenting baker s yeast gives (5)-B. Synthesis of (2S,6R,8S)-88 was executed as a part of this project (Figure 4.35).64,65... 

The conformation of 17-cp/-deoxysalinomycin (a close relative of the antibiotic) has a definite form in solution but it cannot exist as a head-to-tail hydrogen-bonded structure. The relevance of these deductions to its biological role has been discussed. One of the constituents of the secretion of the bee Andrena wilkella is the bis-spiropyran (7), and this has been synthesized from ethyl (+)-(5 )-3-hydroxybutenoate, obtained from the reduction of ethyl acetoacetate by yeast. ... 

The Ci4 intermediate (X = Br) resulting from treatment of the building block with the Cg unit Scheme 43) reacts with the C4 unit, obtained by reduction of ethyl acetoacetate by yeast (Y) to give the C g intermediate. This is then transformed into the hydroxyalkyl-substituted phenol of Scheme 40. 

A mild and inexpensive way to reduce aldehydes or ketones uses fermenting Baker s yeast. This is a whole-cell system that contains oxidoreductase enzymes and cofactors that reduce the substrate. The ketonic carbonyl groups of (3-keto-esters and cyclic ketones are reduced with high selectivity using Baker s yeast. Typical in this regard is the reduction of ethyl acetoacetate, which gives ethyl 3-hydroxybutyrate as predominantly the (5)-stereoisomer (7.101). Similarly, the ketone 114 gave the optically active 3-hydroxyproline derivative 115 (7.102). 

A detailed recipe has been given for the reduction of ethyl acetoacetate to ethyl-(S)-3-hydroxybutanoate (118) by Baker s yeast.Various forms of immobilized Baker s yeast can also be used,117 resulting in improved optical yields in some cases. 

The alkyl esters of 3-hydroxybutanoic acid are a particularly useful group of compounds in organic synthesis because they are available in both chiral forms. Ethyl (5)-3-hydroxybutanoate, for example, may be prepared by the reduction of ethyl acetoacetate on the re side of the keto group with fermenting yeast and leads to an enantiomeric purity of about 85% which may be enriched further via a crystalline dinitrobenzoate. Synthesis of the R form was a little more difficult but could be achieved with 83-88% purity by the reduction of the acetoacetate with hydrogen in the presence of Raney nickel which had been treated with tartaric acid. " ... 

Reduction of ethyl acetoacetate with Aspergillus niger gives 98% of a 75 21 mixture favouring (R)-alcohol. This is in contrast to the formation of (S)-alcohol with Baker s yeast or geotrichum candidum. ... 

Hydroxy-esters.—Ethyl 5-3-hydroxybutanoate is obtained in 87% optical purity by the reduction of ethyl acetoacetate with Bakers yeast. " Two independent chiral synthesis of the leukotriene intermediates (46), R = CHO and R = CH2OH, have appeared. An effective large-scale conversion of arachidonic acid into 5-hydroxy-6-fran5-8,ll,14-cis-eicosatetraenoicacid (5)HETE, including its resolution, is also reported by Corey and Hashimoto. ... 

Ethyl (5 )-3-hydroxybutanoate (3), obtained from the reduction of ethyl acetoacetate with bakers yeast, is readily converted into the tosylate (4). Its reaction with a lithium dialkylcuprate occurs with inversion of configuration to provide the acid (5) in 88—84% optical purity for three examples (Scheme 3). ... 

At this stage a very slight trace of ethyl acetoacetate could be seen by TLC and to assist further reduction more sucrose (25 g) and yeast (10 g) were added. The reaction was then stirred at 30 °C for 18 hours. 

As a result of the easy accessibility of fi-hydroxy carboxylates, even in their nonraccmic form, and also the predictable and high level of diastereoselectivity in the alkylation of their corresponding dianions, this methodology has become a broadly used synthetic tool (see Tables 1-3). (3S>11, the yeast reduction product of ethyl acetoacetate, is methylated in 68% yield with a d.r. of 95.5 4.5 via the lithium dianion with iodomethane16. 

Interestingly, reduction of ethyl 4-chloroacetoacetate with Baker s yeast gave predominantly the corresponding (5)-alcohol (i.e. the opposite configuration from that of the alcohol from ethyl acetoacetate itself) (7.103), but the corresponding octyl ester gave almost entirely the (/f)-alcohol. The stereochemistry of the reduction depends on the shape of the molecule and it is likely that the yeast contains at least two different oxidoreductase enzymes which produce the two enantiomeric alcohols at different rates. 

Day 1 of fhe experiment involves setting up the reaction. Another experiment can be conducted concurrently with this experiment. Part of this first laboratory period is used to mix the yeast, sucrose, and ethyl acetoacetate in a 500-mL Erlenmeyer flask. The mixture is stirred during part of that first period. The mixture is then covered and stored until the next period. The reduction requires at least 2 days. 

In general, these reductions arc only partially, not completely, optically selective, though the formation of practically pure (- -)-/S-hydroxy-n-butyric acid by the action of fermenting yeast on the potassium salt of ethyl acetoacetate has been claimed by Friedmann (41). 

The ordinary yeast used by bakers in their bread making is a valuable organism for the enantioselective reduction of unsymmetrical ketones.2 It is particularly efficient at the reduction of P-keto-esters such as ethyl acetoacetate 1. An Organic Synthesis procedure3 reveals that the true reagent is sucrose, which provides just one H atom, that plenty of yeast is required, and that 3-4 days are needed to make 20-30 g product 2 in only 85% ee. 

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