Baker's yeast catalyzed asymmetric reduction of prochiral ketones in different reaction mediums

Baker’s yeast catalyzes the asymmetric reduction of prochiral ketones in water and in various organic solvents. The reaction in water, which is the first solvent of choice for bio-reactions, led to a high product yield and enantiomeric excess, but the low miscibility of organic molecules in water resulted in lower conversions when more hydrophobic ketones were used. Petroleum-based solvents such as hexane and petroleum ether were also successfully employed as reaction mediums, but the viability of the yeast in these solvents was negligible, and they have severe environmental impacts due to their high toxicity levels. Performing the reaction in green solvents, like ionic liquids, fluorous media, and glycerol-based solvents, which have low volatilities and can be recycled, enabled dissolution of the substrates and of the energy source and also promoted isolation of the product. Among all tested green solvents, glycerol-based solvents are preferable due to their biodegradable natures and their origins from renewable sources.