Studies On Microbial Transformation And Isomerization Of Curdione

Curdione is a main ingredient of Ezhu essential oil and reported to possess wide range of pharmacological activities including anti-inflammatory, anticancer, hepatoprotective and antithrombotic activities. It has been reported to be transformed into corresponding saturated alcohols and epoxides by various microorganisms. However, the transformation pathways of the curdione in fungal systems and the conversion of epimers of the curdione have not been sufficiently investigated.Three microorganisms (Cunninghamella elegans AS3.2028, Mucorpolymorphosporus AS3.3443and Aspergillus niger AS3.739) with the ability to transform the curdione were screened out from twenty-two filamentous fungi. The curdione was completely transformed by the A. niger AS3.739, and compared with the other two microorganism, more products of the transformation by the A. niger AS3.739were yielded. Therefore the A. niger AS3.739was selected for the further investigations. The structures of the products isolated from culture of the A. niger AS3.739were determined on the basis of chemical and spectroscopic data such as MS, NMR, IR and CD. The products were identified as:curcumalactone (1),3a-hydroxycurcumalactone (2),3a-hydroxycurdione (3),2β-hydroxycurdione (4),(10S)-9,10-dihydroxy-curcumalactone (5) and (10R)-9,10-dihydroxy-curcumalactone (6). The above products included two compounds with germacrane-type skeleton (3,4) and four compounds with spirolactone-type skeleton (1,2,5and6) wherein the compounds (2,5and6) are new compounds.A tentative metabolic pathway for the transformation of the curdione via chemo-bio cascade reactions was proposed based on the TLC and HPLC results of biotransformations of the curdione by growing cells of the A. niger AS3.739and the relationships of the biotransformation products investigated by acid-catalyzed transformations. The quantity of the curdione decreased dramatically at the beginning of the culture and was undetected after48h. The curdione was hydroxylated at C-2β and C-3a by the A. niger AS3.739to yield the compounds3and4. The compound1further underwent transformation by the A. niger AS3.739as well as acid-catalyzed reaction leading to the formation of the compounds (5and6). Subsequently the compound3was subjected to isomerization reaction under the acid catalysis, and furthermore the spirolactone type compound (2) was generated. However the compound4with the same skeleton as the curdione and the compound3couldn’t be transformed into corresponding spirolactone under this conditions.In addition,4-epi-curdione (11) as the C-4epimer of the curdione synthesized from the curdione was specifically transformed into4-epi-curcumalactone (13) via acid-catalyzed isomerization. Neocurdione (12) isolated from the Ezhu essential oil was specifically transformed to neocurcumalactone (14) also via acid-catalyzed isomerization. The NMR data and the optical rotation value showed that4-epi-curdione (11) was the enantiomer of the neocurdione (12), and4-epi-curcumalactone (13) as the transformation product of the4-epi-curdione (11) was the enantiomer of neocurcumalactone (14). The two pairs of the enantiomers were analyzed by chiral HPLC columns, and the analyze result showed that:4-epi-curdione (11) and neocurdione (12) could be separated by a Chiralpak AS-H column, and4-epi-curcumalactone (13) and neocurcumalactone (14) could be separated by a Chiralpak AD-H column.