Stereoselective epoxidation of curcumol and curdione by Cunninghamella elegans AS 3.2028

Sesquiterpenes such as curcumol (1) and curdione (2) are the major ingredients of Rhizoma curcumae. Compounds (1) and (2) are isomers of one another and play important roles in Chinese Traditional Medicine. Microbial transformations of naturally occurring curcumol and curdione by Cunninghamella elegans AS 3.2028 were studied. In this research, stereoselective epoxidation at the double bond of curcumol led to 10S,14-epoxycurcumol (3) as the major metabolite, with no detectable 10R,14-epoxycurcumol (4). Epoxidation also occurred at the double bond of curdione, generating both (1S,10S)- and (1R,10R)-1,10-epoxycurdione (5) and (6). The diastereomeric excess (de) of the S diastereomer was 27%. The selectivity of the biotransformation is discussed.