Medson, Caroline (2000) Parameters influencing yeast-mediated reactions in an organic solvent. PhD thesis, Victoria University of Technology.

Abstract

The yeast-mediated reduction of a series of 3-oxobutanoate esters (methyl, ethyl, isopropyl, butyl, sec-hutyl, tert-hutyl and benzyl) was performed in petroleum ether at room temperature over a 24h period. The procedure was shown to be a simple and effective method for the stereoselective preparation of (5)-3-hydroxybutanoates. Of the seven esters tested, the best substrate was shown to be the isopropyl ester, which gave the best yield (96%) with a relatively small amount of yeast (2g/mmole substrate) and with good enantioselectivity (97% ee). Although some esters required larger amounts of yeast in order to attain complete conversion to the product, the isolated yields were generally higher than 70% and the enantioselectivity was normally greater than 97% ee. The yields and stereoselectivity obtained using this method are superior to those reported for reductions using fermenting yeast in an aqueous environment. The results suggest that substrate size and shape have an impact on the ease of binding of the substrate to the active site of the enzyme system; substrates which bind poorly require more yeast.

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