Biotransformation of imperatorin by Aspergillus flavus.

Imperatorin (1) was metabolized by Aspergillus flavus, in growth media, to give five metabolites. On the basis of their physical data, the structures of the five metabolites were elucidated as xanthotoxol (2), E-trichoclin (3), Z-trichoclin (4), E-imperatorin acid (5), and Z-imperatorin acid (6); among these, 4, 5, and 6 were characterized as new coumarins. The five metabolites 2-6 were tested for anti-hepatitis B virus activity in vitro and found to be less active than the parent compound 1.