Amiaspochalasins I and J, Undescribed Aspochalasins with Antibacterial Activities From Aspergillus micronesiensis.

Two undescribed aspochalasins named amiaspochalasins I and J (1 and 2), along with a known analogue named aspochalasin U (3) were isolated from the endophytic fungus Aspergillus micronesiensis. Their structures including absolute configurations were elucidated by extensive NMR data, molecular modelling studies, and electronic circular dichroism (ECD) calculations. Usually, there is a double bond at Δ6 in the core structure of aspochalasins, while in compounds 1-3, this double bond has shifted to Δ5. Compound 1 is the first aspochalasin bearing a carbonyl at C-7, and compound 2 has an additional hydroxyl at C-17 in comparison of aspochalasin U (3). Compounds 1-3 showed moderate inhibitory effects on Staphylococcus aureus, Escherichia coli, and Salmonella enterica, and the MIC values of 1-3 against Staphylococcus aureus were 32, 64, and 64 µg mL-1, respectively.