4- Chloro-3-oxobutanoate esters

Fig. 42 Stereospecific reduction of 4-chloro-3-oxobutanoate ester (COBE) to (K) and (S)-4-chloro-3-hydroxybutanoate ester (CHBE) by aldehyde reductase from Sporobolomyces salmonicolor and carbonyl reductase from Candida magnoliae, respectively...

Recently, we [67] have described the reduction of the methyl ester of 4-chloro-3-oxobutanoic acid (39) to the methyl ester of S-( )-4-chloro-3-hydroxy-butanoic acid (40) (Fig. 13) by cell suspensions of Geotrichum candidum SC 5469., S ( )-(40) is a key chiral intermediate in the total chemical synthesis of a cholesterol antagonist (SQ 33600), which acts by inhibiting hydroxymethylglu-taryl CoA (HMG CoA) reductase. In the biotransformation process, a reaction... 

Figure 13 Synthesis of chiral synthon for anticholesterol drug SQ 33600 stereoselective microbial reduction of 4-chloro-3-oxobutanoic acid methyl ester (39).

Glucose-grown cells of G. candidum SC 5469 have also catalyzed the stereoselective reduction of ethyl-, isopropyl-, and tertiary-butyl esters of 4-chloro-3-oxobutanoic acid and methyl and ethyl esters of 4-bromo-3-oxobutanoic acid. A reaction yield of >85% and e.e. of >94% were obtained. NAD+-depen-dent oxido-reductase responsible for the stereoselective reduction of P-keto esters of 4-chloro- and 4-bromo-3-oxobutanoic acid was purified 100-fold. The molecular weight of purified enzyme is 950,000. The purified oxido-reductase was immobilized on Eupergit C and used to catalyze the reduction of (39) to S-( - )-(40). The cofactor NAD+ required for the reduction reaction was regenerated by glucose dehydrogenase. 

In another study, screening was carried out for reduction of substituted benzazepin-2,3-dione 23 to a 3-hydroxy derivative 24 (Scheme 19.14). This was accomplished by a bacterial strain of Rhodococcus fascians ATCC 12975 (Norcardia salmonicolor SC 6310) with a conversion of 97% and an optical purity of >99.9%. This reaction product 24 is a key intermediate in the synthesis of the calcium antagonist SQ 31,765 (25).104 105 The Bristol-Myers Squibb group has also shown the selective reduction of the (3-keto ester, methyl-4-chloro-3-oxobutanoate, by the fungus Geotrichum candidum SC 5469 to the corresponding (,S )-hydroxy ester.106... 

This microflow processing was also demonstrated using other P-keto esters such as ethyl 2-chloro-3-oxobutanoate [309,273] or ethyl 2-methyl-3-oxobutanoate [273]. Five-and six-ring P-ketoester derivatives such as 3-acetyl-3,4,5-trihydrofuran-2-one (1) [273], 2-acetyl cyclohexanone [273] and ethyl 2-oxocydohexane carboxylate (2) [273] were directly fluorinated as well. 

The enantioselectivity of a biocatalytic reduction can be controlled by modifying the substrate because the enantioselectivity of the reduction reaction is profoundly affected by the structure of substrates. For example, in the reduction of 4-chloro-3-oxobutanoate by bakers yeast, the ester moiety can be used to control the stereochemical course of the reduction 161 531. When the ester moiety was smaller than a butyl group, then (Sj-alcohols were obtained, and when it was larger than a pentyl group then (R)-alcohols were obtained as shown in Fig. 15-9. 

The direct alkylation of hydrogenphosphonic diesters with a diazoketone has been recorded alongside that with diazoalkanoic esters, and explored particularly with methyl 2-diazo-3-oxobutanoate but also for several chloroacetones. Reactions involving 1-chloro-3-diazo-2-propanone are effectively catalysed by [Cu(acac)2], but more heavily chlorinated substrates suffer stepwise dechlorination. Thus l,l,l-trichloro-3-diazo-propan-2-one initially yields the expected dialkyl (3,3,3-trichloro-2-oxopropyl)phospho-nate, but under the experimental conditions, dechlorination then proceeds to give the dialkyl (3,3-dichloro-2-oxopropyl)phosphonate only the monochloroketone undergoes a reaction in which the original halogen content is retained in the final product ... 

The pyrimidine part (4,5-dichloro-6-methylpyrimidine, 11) is synthesized in a two-step sequence starting with the condensation of 2-chloro-3-oxobutanoic acid methyl ester (8) and formamidine acetate 9 [15] to give 5-chloro-4-hydroxy-6-methylpyrimidine (10) in high yield, followed by the chlorination of the hydroxy group using standard synthesis methodology [15-18]. Synthesis of the sub-... 

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... 

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