Background

Bakers’ yeast (yes… the bakers’ yeast you buy at your local grocery store) has been used as a biocatalyst for over 100 years. It has been shown to catalyze the forming and breaking of C-C bonds, oxidations, hydrolysis and the most popular use would be the utilization of their abundant reductases. Recent work at the University of Florida yielded engineered E. coli that overexpress a single bakers yeast reductase. This affords a ‘green chemical’ route to screen a single reductase for its ability to asymmetrically reduce a prochiral substrate. We have used this strategy for the synthesis of biologically active molecules such as Bestatin^® (Tetrahedron: Asymmetry. 16(18), 2005, 3124) and the side chain for the highly successful cancer drug, Taxol^® (J. Org. Chem. 70(23), 2005, 9654).

Biochemistry & Molecular Biology

These engineered E. coli have been a significant improvement when compared to bakers’ yeast. Unfortunately, there are still stereochemical products that are not formed by our library of enzymes. We are working in conjunction with Dr. Scott Mateer’s lab (AASU – Biology), on the engineering of second-generation biocatalysts. Computer models are being used to understand enzyme folding and active site docking for specific substrates. We are also introducing systematic point mutations on these reductases. Our goal is to enhance and grow our library of reductases, thus increasing the organic chemists’ asymmetric toolbox.

Bio-organic Chemistry

Bioreduction of β -keto nitriles

The synthesis of asymmetric molecules plays a large role in our research. The reduction of β-keto nitrile (1) to yield β-hydroxy nitrile (2), and the formal synthesis of both enantiomers of Prozac has just been completed (Scheme 1). In addition, the reduction of other nitriles and their uses are being investigated.

Bioreduction of oximes

The reduction of ketones using biocatalysis has been investigated thoroughly. However, the reduction of C=N double bonds (like oximes) has been almost ignored. It is our goal to show that these ‘keto reductases’ are not limited to the ketone functionality and hopefully expand their present definition as ketone/oxime reductases. If successful, not only will we have a better understanding of these versatile reductases, but it will also allow for the synthesis of a variety of chiral amines (Scheme 2).

Synthesis of Lactones

We are presently investigating the synthesis of chiral lactones, which are known to have a variety of pharmacological effects. Our strategy is to start with the optically pure hydroxy nitriles formed in Scheme 1. Rhodococcus rhodocrous, an organism known to contain large amounts of nitrilase, is then used to afford the acid. These acids make excellent precursors to optically active lactones (Scheme 3).