Microbial stereoinversion

Deracemization via the biocatalytic stereoinversion is usually achieved by employing whole cells. In the case of secondary alcohols, it is believed that microbial stereoinversion occurs by an oxidation-reduction sequence... 

Keywords Microbial, Stereoinversion, Deracemization, Redox, Epimerase. 

Microbial stereoinversion consists of a deracemization process in which a single whole cell system is applied for the two-step inversion of the configuration of one enantiomer, usually a compound containing a secondary alcohol group. Examples of a two-enzyme system is known for deracemization of mandelates where a single microorganism is used [18]. 

Scheme 13.7 Hydroxy acids produced by microbial stereoinversion.

Microbial stereoinversion has been shown to be extremely flexible, as it is also applicable to sec-diols possessing two stereocenters (Scheme 2.132) [958-960]. Thus, meso- or rac-/rans-cyclohexane-l,2-diol was deracemized by... 

Hasegawa J, Ogura M, Tsuda S, Maemoto S, Kutsuki H, Ohashi T. High-yield production of optically active 1,2-diols from the corresponding racemates by microbial stereoinversion. Agn c. Biol Chem. 1990 54 1819-1827. 

An alternative approach to the microbial deracemization of secondary alcohols is to use two different microorganisms with complementary stereoselectivity. Fantin et al. studied the stereoinversion of several secondary alcohols using the culture supernatants of two microorganisms, namely Bacillus stearothermophilus and Yarrowia lipolytica (Figure 5.18) [31]. The authors tested three main systems for deracemization. First, they used the supernatant from cultures of B. stearothermophilus, to which they added Y. lipolytica cells and the racemic alcohols. Secondly, they used the culture supernatant of Y. lipolytica and added B. stearothermophilus cells and the racemic alcohols. Finally, they resuspended the cells of both organisms in phosphate buffer and added the racemic alcohols. The best results were obtained in the first system with 6-penten-2-ol (26) (100% ee and 100% yield). The phosphate buffer system gave... 

Carnell, A. J. 1999. Stereoinversions using microbial redox-reactions. Adv. Biochem. Eng. Biotechnol., (Biotrans.), 57-72. 

Fig. 4. (A) Synthesis of chiral intermediates for melatonin receptor agonist Enantioselective microbial hydrolysis of racemic epoxide US) to the corresponding (/ )-diol (14) and unreacted (5)-epoxide (12). (B) Stereoinversion of racemic diol (16) to 5-diol (15) by Candida boidinii and Pichia methanolica.

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