Enantioselective yeast hydrolysi

Summary rac-l-(4-Fluorophenyl)-l-methyl-l-sila-2-cyclohexanone (rac-1) and rac-(SiS, C/ /Sii ,CS)-2-acetoxy-l-(4-fluorophenyl)-l-methyl-l-silacycIohexane [rac-(Si5,Ci /Siiil,C5)-3a] were synthesized as substrates for stereoselective microbial transformations. Resting free cells of the yeast Saccharomyces cerevisiae (DSM 11285) and growing cells of the yeasts Trigonopsis variabilis (DSM 70714) and Kloeckera corticis (ATCC 20109) were found to reduce rac- diastereoselectively to yield mixtures of the enantiomers (S S,CR)- and (SLR,C5)-l-(4-fluorophenyl)-l-methyl-1-sila-2-cyclohexanol [(Si5,C/ )-2a and (SLR,CS)-2a]. In the case of Kloeckera corticis (ATCC 20109), diastereoselective reduction of rac-1 gave a quasi-racemic mixture of (Si5,CR)-2a and (SiR,CS)-2a (diastereomeric purity 95 % de, yield 95 %). Enantioselective ester hydrolysis (kinetic resolution) of the 2-acetoxy-l-silacyclohexane rac-(Si5,CR/Si/ ,C5)-3a yielded the optically active l-sila-2-cyclohexanol (Si/ ,C5)-2a [enantiomeric purity >99% ee yield 56 % (relative to (Si, C5)-3a)]. 

The yeast Pichia pijperi (ATCC 20127) was found to be a highly effective biocatalyst for the enantioselective ester hydrolysis (kinetic resolution) of the 2-acetoxy-l-silacyclohexane rac-(Si5, C/ /Si/ ,C5)-3a (Scheme 3). 

Very few optically active cyanohydrins, derived from ketones, are described in the literature. High diastcrcosclectivity is observed for the substrate-controlled addition of hydrocyanic acid to 17-oxosteroids27 and for the addition of trimethyl(2-propenyl)silane to optically active acyl cyanides28. The enantioselective hydrolysis of racemic ketone cyanohydrin esters with yeast cells of Pichia miso occurs with only moderate chemical yields20. 

While enantioselectivity during reduction of ethyl 3-oxobutanoate by baker s yeast (Saccharomyces cerevisiae) to ethyl (S)-3-hydroxybutanoate was found to exceed 99%, yields did not exceed 50-70% (Chin-Joe, 2000). Elimination of two of three causes, evaporation of substrate and product esters and absorption or adsorption of the two esters by the yeast cells, increased the yield to 85%. Alleviation of hydrolysis of the two esters by yeast enzymes could increase the yield even more. Low supply rates of glucose as an electron donor provided the most efficient strategy for electron donor provision and yielded a high enantiomeric excess of ethyl (S)-3-hydroxybutanoate, low by-product formation and biomass increase, with a low oxygen requirement(Chin-Joe, 2001). 

The enantioselective hydrolysis of the key industrial starting compound methyl benzoate 41 was recently reported using a Candida rugosa isoenzyme LIP1 expressed in the methylotrophic yeast Pichia pastoris affording /-menthol 28 with > 99% ee. 69... 

Hydrolyses. The presence of hydrolytic enzymes in BY is well documented. However, the use of the yeast for biocatalytic ester hydrolysis suffers because of the availability of commercially available purified hydrolases. Nonetheless, the hydrolytic ability of fermenting BY has been proposed for the resolution of various amino acid esters (eq 14). The BY-mediated enantioselective hydrolysis has also been applied to the resolution of acetates of hydroxyalkynes and a hydroxybutanolide. ... 

Fig. 18. Yeast epoxide hydrolase. Enantioselective hydrolyses of aromatic [194] and aliphatic [194, 195] epoxide using whole cells of Rhodotorula glutinis. Stereoselective hydrolysis of cyclopentene oxide [194]...

Enzymatic cnantioface-differentiating hydrolysis constitutes another promising route to ketones with a stereogenic center in the a-position. Through broad screening a type of yeast was selected for enantioselective hydrolysis of cyclanone enol ester178. 

Enantioselective Hydrolysis of Ketoprofen Esters Using Yeast Cells... 

Although the catalytic activity of T. brassicae CGMCC0574 whole cells in the enantioselective hydrolysis of ketoprofen ester was initially moderate, it was significantly promoted after the cells were pretreated for a few hours in a buffer containing an alcohol as the modulator. This suggested a possible permeability barrier from the cell membrane against the mass transfer of substrates and/or products. Therefore, the permeabilization of the yeast cells was considered to be favorable for the enzymatic resolution of ketoprofen. 

As mentioned above, ketoprofen is widely used in clinical practice as a nonsteroidal anti-inflammatory drug, like the other 2-arylpropionic acids such as naproxen and ibuprofen. The anti-inflammatory activity of ketoprofen was previously believed to reside in its (S)-enantiomer. However, research has indicated that the (f )-enantiomer of ketoprofen was able to prevent periodontal disease and was thus of pharmacological value as a toothpaste additive. It has also been discovered that (i )-ketoprofen has several previously unappreciated advantages as an analgesic and antipyretic. Another yeast strain, Citeromyces matriemis CGMCC 0573, was therefore isolated for the enantioselective hydrolysis of (i )-ketoprofen ethyl ester. ... 

Disubstituted aliphatic oxiranes have been reported to be hydrolyzed by EHs from fungi [131], yeast, and bacteria. The most interesting results were observed with yeast and bacterial EHs. As far as kinetic resolution is concerned, it was shown by Weijers [116] that R. glutinis catalyzed the enantioselective hydrolysis of cis-2,3- and trans-2,3-epoxypentane, resulting in residual (2R)-epoxides with yields that approached the theoretical maximum of 50%. More interestingly, biocatalytic transformations of racemic 2,3-disubstituted oxiranes to vicinal diols with high ees at... 

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