Isolation and Photoinduced Conversion of 6-<i>epi</i>-Stephacidins from <i>Aspergillus taichungensis</i>

Three prenylated indole alkaloids with a rare anti bicyclo-[2.2.2]diazaoctane core ring (5–7) were isolated from Aspergillus taichungensis. The structures including absolute configurations were elucidated based on NMR, X-ray, and CD methods. (+)-Versicolamides B and C (8–9) which contain a spiro-center, together with seven analogues (7, 10–15), were isolated as photoinduced conversion products of 6. Biological evaluation indicated that 6 and 7 exhibited significant cytotoxicities with IC50 values in the low micromolar range.