Use of Enzymes in Organic Synthesis: Reduction of Ketones by Baker's Yeast Revisited

Abstract

The undergraduate organic laboratory “Baker’s Yeast Reduction of Ethyl Acetoacetate” has been improved in two different ways. First, the addition of small quantities of hexane to the aqueous yeast system along with an improved workup protocol has dramatically increased the yield and reproducibility of the ketone conversion to the corresponding alcohol with a high enantiomeric excess. Second, the enantiomeric excess of the alcohol product was ascertained by coupling the alcohol mixture with a chiral acid and analyzing the resulting mixture of diastereomeric esters by proton NMR. The relative quantities of diastereomers were derived from integration values of the NMR spectra. These modifications of the Baker’s yeast reduction lab enhance its overall suitability as an undergraduate laboratory in 3 main ways; increased yield and recovery of alcohol product, ease of analysis of the enantiomeric excess, and an interesting and advanced NMR spectral analysis involving ABX coupling systems.