An insight into the curdione biotransformation pathway by <i>Aspergillus niger</i>

<div><p>Curdione (<b>1</b>), a sesquiterpene with a germacrane skeleton from rhizomes of <i>Curcuma wenyujin</i>, has attracted attention due to its important pharmacological properties. Herein, we investigated the chemo-biotransformation of curdione (<b>1</b>) systematically using <i>Aspergillus niger</i> AS 3.739. Regio- and stereoselective hydroxylation of curdione with filamentous fungus <i>A. niger</i> AS 3.739 led to seven metabolites including four new compounds 3α-hydroxycurcumalactone, 2β-hydroxycurcumalactone, (10<i>S</i>)-9,10-dihydroxy-curcumalactone and (10<i>R</i>)-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 <i>A. niger</i> 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.</p>