Three alkaloids and one polyketide from Aspergillus cristatus harbored in Pinellia ternate tubers

Three new indole diketopiperazine alkaloids, aspergillines A-C (1–3), together with one new polyketide, aspergillone A (4), were isolated from the solid cultures of an endophytic fungus Aspergillus cristatus. Aspergilline A is the first bicyclo[2.2.2] diazaoctane indole alkaloid where the diketopiperazine structure is constructed from tryptophan and alanine. The structures were determined by spectroscopic analysis and their absolute configurations were determined through single-crystal X-ray diffraction and electronic circular dichroism (ECD) spectroscopy. Aspergillone A exhibited moderate antibacterial activities against Bacillus subtilis and Staphylococcus aureus with MIC50 values of 8.5 and 32.2 μg/mL, respectively.