Secondary microbial deracemization

Microbial Deracemization of Secondary Alcohols Using a Single Microorganism... 

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... 

Allan GR, Camell AJ. Microbial deracemization of 1-aryl and 1-heteroaryl secondary alcohols. J. Org. Chem. 2001 66 6495-6497. 

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... 

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]. 

It is well known that various microbial systems are able to deracemise racemic secondary alcohols via a process that generally involves two different alcohol dehydrogenases with complementary enantiospecificity. For example racemic benzoin may be deracemized using Rhizopus oryzae ATCC 9363 (Scheme 4.38). Interestingly, through control of the pH of the medium, it was possible to control the absolute configuration of the major enantiomer produced at pH 7.5-8.S, the (J )-enantiomer was produced in 75% yield and 97% ee whereas at pH 4-5, the (S)-enantiomer was produced in 71% yield and 85% ee [89]. 

---