Reductions of 3-oxo esters by baker's yeast: Current status

The objective of the current review is lo present a mechanism and process engineering approach of stereospecific reductions of 3-oxo esters by baker's yeast. The stereospecific outcome of a reduction by baker's yeast depends on the kind of 3-oxo ester reductases involved and their specific activity. Various competing 3-oxo ester reductases are present in a yeast cell. An important aspect for efficient biotransformations with whole cells is the regeneration of NADH and NADPH cofactors. Use of different electron donors leads to the involvement of different metabolic routes influencing the reduction process. Optimization of the process conditions such as aeration, immobilization of cells, use of additives, or use of two phases, will enhance re-use of baker's yeast yield, stereospecific outcome and scale up. Since the genome of baker's yeast is known: genetic engineering will soon increase the possibilities of stereoselective reductions.