Asperginols A and B, Diterpene Pyrones, from an Aspergillus sp. and the Structure Revision of Previously Reported Analogues

Two new diterpene pyrones, asperginols A (1) and B (2), and four known analogues (3–6) were isolated from the endophytic fungus Aspergillus sp. HAB10R12. The structures and absolute configurations of these compounds were elucidated based on the analysis of their NMR, MS, and X-ray diffraction data. The revision of the absolute configurations at C-10, C-11, and C-14 of the known diterpene pyrones (3–6) and the determination of the configuration at the polyene side chain for compounds (4–6) were made using chemical methods and vibrational circular dichroism analysis. This group of diterpene pyrone compounds showed unique structural features including a 7/6/6 tricyclic diterpene moiety with an unusual trans–syn–trans stereochemical arrangement. Compound 6 showed moderate activity against the HT-29 colon cancer cell line.