Microbial transformation studies on arteannuin B

The microbial transformation of the sesquiterpene lactone arreannuin B [3] using Aspergillus flavipes produced dihydroarteannuin B [4] as the main transformation product. Preparative-scale fermentation of 3 with Beauveria bassiana, on the other hand, has resulted in the production of two metabolites, 3 beta-hydroxyarteannuin B [5] and 13-hydroxy-11-epi-dihydroarteannuin B [6]. The structure of these metabolites, all of which are new compounds, was established using chemical and spectroscopic techniques. The isomeric dihydrocompound, 11-epi-dihydroarteannuin B [7] and an isomer of arteannuin B [8] were also prepared chemically. All compounds were subjected to 2D-nmr experiments and full 1H- and 13C-nmr assignments were made.