Redox enzymes used in chiral syntheses coupled to coenzyme regeneration

Due to their ability to perform reactions in a stereo- and regiospecific manner, while functioning under mild conditions of temperature and pH, enzymes are increasingly used for chiral synthesis in the pharmaceutical industry, in medicinal chemistry, agriculture, cosmetic and food industry. The oxidoreductases as catalysts require a coenzyme (cofactor) which functions as an electron carrier. If used in stoichiometric amounts the cost of coenzymes makes synthetic applications of redox enzymes prohibitively expensive for industrial applications. The present review updates previous discussions about the objectives of cofactor regeneration as a requirement for the applicability of enzymatic redox reactions, and about the strategies customarily used to this end. Different types of chiral syntheses coupled successfully to coenzyme regeneration (amino acid synthesis, lactone synthesis, synthetic reactions involving alcohols, hydroxy acid and steroid synthesis, deracemization) are then discussed. New catalysts, cross-linked enzyme crystals, prepared from redox enzyme are presented in a small paragraph together with some of their applications. Special attention is given to whole cells used in this type of synthesis and their advantages and disadvantages are presented in one paragraph. Finally, different reactors, within which were conducted chiral syntheses catalyzed by oxireductases and coupled to cofactor regeneration, are briefly discussed.