Yeast-Mediated Reactions in Organic Solvents

Abstract

The use of baker’s yeast as a reagent in organic synthesis has been well documented (1,2). Yeast is capable of catalyzing a wide range of different types of reactions although it is most commonly used for the asymmetric reduction of carbonyl groups and alkenes. By far, the majority of yeast-mediated reduction reactions have been conducted using fermenting yeast in an aqueous reaction system. Reactions of this type involve the addition of yeast and nutrient, glucose or sucrose, to a buffered solution followed by the addition of the substrate. Under these conditions, the yeast is actively growing, all of the biochemical pathways are operating, and, as part of the fermentation process, the substrate is converted into the desired product, usually with a high degree of stereoselectivity. Although this methodology is well established and in many cases highly successful, it does have a number of inherent experimental problems. The use of an aqueous environment for transformations involving organic substrates is undesirable, because of the limited water solubility of many substrates. The greatest problem, by far, associated with the use of yeast in aqueous systems is the isolation of the product. At the end of the reaction, the yeast mass is finely dispersed throughout the water and this makes filtration of the yeast and extraction of the product a difficult procedure. In addition, the fermenting yeast has produced a range of metabolic products that will need to be separated from the desired product.