Figure 2.4 Enantiomeric pairs of thalidomide.

The rapidly growing field of biotechnology brings with it opportunities in the field of enzyme-catalyzed reactions. The role of genetically engineered microorganisms in synthesizing rare and valuable peptides used in human therapeutics is now well established. The same techniques of molecular biology can also be used to enhance the properties of enzymes as catalysts for industrial processes that are very similar to classic catalytic technology.

This approach can potentially revolutionize the applications of biological systems in catalysis. Enzymes and other biological systems work well in dilute aqueous solution at moderate temperature, pressure, and pH. The reactions catalyzed by these systems are typically environmentally friendly in that few by-products or waste products are generated. The catalysts and the materials that they synthesize are, as a rule, biodegradable and therefore do not persist in the environment. The reactions are typically selective with extremely high yields, and enzymes can be used to catalyze a whole sequence of reactions in a single reactor, resulting in vastly improved overall yields with high positional specificity and 100% chiral synthesis in most cases. The improved use of enzyme catalyst technology with whole-cell catalysis, reactions catalyzed by single enzymes, and mixed enzymatic and chemical syntheses are all important for the development of new catalyst technology.

Whole cells of various microorganisms are being used more frequently in the catalytic synthesis of complex molecules from simple starting materials. The use of whole microbioal cells as biosynthetic catalysts takes advantage