Three Dimeric Naphtho-γ-Pyrones from the Mangrove Endophytic Fungus Aspergillus tubingensis Isolated from Pongamia pinnata

Three new dimeric naphtho-gamma-pyrones, named rubasperone A (1), rubasperone B (2), and rubasperone C (3), together with two known compounds, rubrofusarin (4) and rubrofusarin B (5), were isolated from the mangrove endophytic fungus Aspergillus tubingensis (GX1-5E). Their structures were determined by spectroscopic methods, including IR, MS, and 1D and 2D NMR. The structures of 1 and 2 were further confirmed by X-ray crystallography. In the bioactivity assays against tyrosinase and alpha-glucosidase, rubrofusarin (4) exhibited moderate tyrosinase inhibitory activity, with an IC50 value of 65.6 mu M, and rubasperone C (3) showed mild alpha-glucosidase inhibitory activity, with an IC50 value of 97.3 mu M.