Structures and Absolute Configurations of Penicillactones A–C from an Endophytic Microorganism, Penicillium dangeardii Pitt

Penicillactones A–C (1–3) are structurally related natural products with a spirocyclic anhydride structure and were isolated from the endophytic fungus Penicillium dangeardii Pitt. Penicillactones B and C showed inhibition of the release of β-glucuronidase from polymorphonuclear leukocytes with ED50 values of 2.58 and 1.57 μM. A 2D INADEQUATE experiment of 1 was performed at natural abundance to confirm the arrangement of its carbon skeleton. The configurations of 1–3 were established through extensive NMR spectroscopic analysis, selective structural modifications, and CD analysis.