Ethyl 4-chloroacetoacetate, reduction

Lactobacillus kefir was also employed as the whole-cell biocatalyst for the asymmetric reduction of ethyl 4-chloroacetoacetate to ethyl (.S )-4-chloro-3-hydroxybutanoate, the chiral... 

Production of Chiral 4-Chloro-3-Hydroxybutanoate Ethyl Ester by Microbial Asymmetric Reduction of 4-Chloroacetoacetate... 

The reduction of 4-chloroacetoacetate ethyl ester (CAAE) to 4-chloro-3-hydroxy-butanoate ethyl ester (CHBE) usually proceeds stereospecifically [54, 55]. This activity is widely distributed in yeasts, molds and bacteria, most of which give the (S)-enantiomer. Sporobolomyces salmonicolor was found to produce the (l )-enan-tiomer predominantly (62% e. e.) with high molar conversion [54,55], and several Candida yeasts formed (S)-CHBE of high optical purity (> 90% e. e.) [54,55]. 

Fig. 11. Priniciple of stereospecific reduction of carbonyl compounds coupled with cofacter regeneration (a) and outline of the stereospecific reduction of ethyl 4-chloroacetoacetate (CAAE) by Sporobolomyces aldehyde reductase (AR) with glucose dehydrogenase (GDH) as a cofactor regenerator in a water-organic solvent two-phasic system (b). CHBE, ethyl 4-chloro-3-hydroxybutanoate...

Metal complexes of C3-TunePhos (110c) have demonstrated high activities (S/C = 45,000) and enantioselectivities (98-99%) in the reduction of ethyl 4-chloroacetoacetate (ECAA).139 Chiral Quest disclosed that this catalyst has been supplied in kilogram quantities to a client for the commercial production of ECHB, which is an intermediate in the production of Lipitor (see Chapter 31).76... 

Fig. 31.23. Synthesis of Ethyl (3S)-4-chloro-3-hydroxybutanoate (ECHB) from Ethyl-4-chloroacetoacetate through whole cell microbial reduction.

When the enantioselective reduction of ethyl 4-chloroacetoacetate was carried out with alcohol dehydrogenase from Candida parapsilosis, the other enantiomer was produced ethyl (P)-4-chloro-3-hydroxybutanoate [134]. This product is a key intermediate in a synthesis of (R)-carnitine. In this case a substrate coupled approach was chosen. The enzyme also has a strong oxidation activity for 2-propanol, which was therefore selected as the cosubstrate. The situation is depicted in Fig. 3.50. Under optimized conditions, the yield of (R)-ethyl-4-chloro-3-hydroxy-butanoate reached 36.6 g L-1 (> 99% ee, 95% yield) on a 30 L scale. 

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. 

KER is a monomeric enzyme whose molecular weight is 36.7 kDa (325 amino acids) and theoretical isoelectric point (pi) is 6.21 (Table 6.3). Purified recombinant KER catalyzes the reduction of BAM and ethyl 4-chloroacetoacetate (CAE) into BHBM and CHBE, respectively, in the presence of NADPH, while NADH does not... 

A first group of ISPR systems, most commonly with reductions, is those using the addition of a resin or porous adsorbent to remove the product. Early work on ketone reduction showed already that hydrolysis and also loss of ee could be overcome by maintaining low concentrations of the substrate in the reaction. One successful approach involves the controlled release of the substrate from a resin placed in the reaction media. For example, Amberlite XAD-2 resin enhanced the asymmetric reduction of ethyl 4-chloroacetoacetate to (S)-4hydroxybutyric acid ethyl ester catalyzed by yeast [34]. In the subsequent development of the technolt, the approach was extended to simultaneous substrate supply and product removal. A similar approach was developed for the asymmetric reduction of 6-bromo-P-tetralone [35]. 

Houng, J.-Y. and Liau, J.-S. (2003) Applying slow-release biocatalysis to the asymmetric reduction of ethyl 4-chloroacetoacetate. Biotechnol. Lett., 25,17-21. 

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