An insight into the curdione biotransformation pathway by Aspergillus niger.

Curdione (1), a sesquiterpene with a germacrane skeleton from rhizomes of Curcuma wenyujin, has attracted attention due to its important pharmacological properties. Herein, we investigated the chemo-biotransformation of curdione (1) systematically using Aspergillus niger AS 3.739. Regio- and stereoselective hydroxylation of curdione with filamentous fungus A. niger AS 3.739 led to seven metabolites including four new compounds 3α-hydroxycurcumalactone, 2β-hydroxycurcumalactone, (10S)-9,10-dihydroxy-curcumalactone and (10R)-9,10-dihydroxy-curcumalactone. Their structures were determined by spectroscopic techniques including two-dimensional NMR and TOF-MS (Time of Flight Mass Spectrometry). Based upon the analysis of biological and chemical conversions of curdione, a tentative metabolic pathway via chemo-bio cascade reactions is proposed in A. niger system, which provides an insight into the corresponding metabolism of curdione in animal systems. In addition, experiments with selected monooxygenase inhibitors suggest that cytochrome P450 monooxygenase played a crucial role in the hydroxylation of curdione.