Azacoccones A-E, five new aza-epicoccone derivatives from Aspergillus flavipes

Azacoccones A-E (1-5), five new aza-epicoccone derivatives, were isolated from the culture of Aspergillus flavipes. Their structures were determined by extensive NMR spectroscopic analyses and the absolute configuration of 5 was determined by electronic circular dichroism (ECD) calculation. Compounds 1-5 are proposed to be generated via a Pictet-Spengler reaction-based biosynthetic route starting from the precursor flavipin. Pictet-Spengler reaction is rarely found in the fungal kingdom, which indicated the distinctive nature of 1-5. Compounds 3 and 5 exhibit significant free radical scavenging activities with IC₅₀ values of 4.0 and 2.4μg/mL, respectively, which are better than the positive control trolox (4.55μg/mL).