초록
<P>Ethyl 4-chloro-3-oxobutanoate (COBE) was asymmetrically reduced with <I>Escherichia coli</I> cells expressing a reductase (ScCR) from <I>Streptomyces coelicolor</I> to afford enantiopure ethyl (<I>S</I>)-4-chloro-3-hydroxybutanoate [(<I>S</I>)-CHBE], which is an important precursor for preparing the drug atorvastatin. The substrate load was fixed at 100 g/L, and the concentration of coenzyme NAD<SUP>+</SUP> was limited to 0.1 mM based on cost considerations. Under these conditions, the other reaction parameters were optimized as 25 °C and pH 6.5, with a biocatalyst dose of 10 kU/L in the presence of isopropanol (1.5 equiv of COBE), which acted as a cosubstrate for regenerating NADH. The reaction was performed in a toluene–aqueous biphasic system (1:1, v/v), with agitation at the maximal linear rate of 0.88 m/s. Finally, the bioreaction was performed on a pilot scale using a 50 L thermostated stirred-tank-reactor, affording (<I>S</I>)-CHBE in 85.4% yield and 99.9% ee, and a total turnover number (TTN) of 6060 for the cofactor NAD<SUP>+</SUP>. The specific production was calculated to be 36.8 g<SUB>product</SUB>/g<SUB>dcw</SUB>, which is the highest value reported to date among the whole-cell-mediated processes for producing (<I>S</I>)-CHBE.</P><P><B>Graphic Abstract</B><BR><IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/oprdfk/2014/oprdfk.2014.18.issue-6/op500088w/production/images/medium/op-2014-00088w_0006.gif'></P>