Enantioselective epoxidation of alkenes by chloroperoxidase and the development of a chloroperoxidase expression system.

摘要

Optically active materials are playing an increasingly important role in industrial, agricultural and medical fields. The synthesis of these compounds has been the focus of a great amount of research. Much of this research has been concerned with the development of chemical catalysts that are capable of inducing chirality into a prochiral compound. Although much progress has been made, there is significant room for improvement in the activity, selectivity, economy and overall usefulness of these catalysts. Enzymes offer a promising alternative to chemical asymmetric catalysts. Being chiral molecules themselves, enzymes routinely catalyze highly stereoselective reactions.; Chloroperoxidase from Caldariomyces fumago has the characteristics of a promising industrial catalyst. Chloroperoxidase is inexpensive to produce and relatively stable and able to catalyze a large number of potentially useful reactions. However, the majority of the reactions studied occur with a lack of any enzyme induced stereoselectivity. Chloroperoxidase, in this report, is shown to catalyze the epoxidation reaction of a number of alkenes in a highly enantioselective manner with enantiomeric excesses between 50% and 97%. Good substrates were generally non-polar cis-alkenes of less than nine carbons in length. Unsubstituted terminal alkenes were shown to inactivate the enzyme. The recent determination of the three dimensional structure by x-ray crystallography and ongoing research in the development of an expression system for chloroperoxidase could open the door for a number of experiments concerning the mechanism of the epoxidation reaction. Also the possibility of improving the utility of chloroperoxidase in asymmetric epoxidations through directed evolution and site-directed mutagenesis remains an exciting prospect for the future.