Studies on pyranonigrins-isolation of pyranonigrin E and biosynthetic studies on pyranonigrin A

摘要

Pyranonigrins A, B, C, D and S have been shown to be secondary metabolites produced by Aspergillus niger LL-LV3020 when grown on a solid culture. The 2,2-diphenyl-l-picrylhydrazyl radical scavenging activity of pyranonigrin A was also reported in previous studies. Pyranonigrins possess unique structures (Figure 1); however, biosynthetic studies on pyranonigrins have not been conducted. We recently found that an acetone extract of A. niger NBRC5374 grown on potato dextrose agar shows a potent 2,2-diphenyl-l-picrylhydrazyl radical scavenging activity and isolated a new pyranonigrin derivative (pyranonigrin E) in addition to pyranonigrins A and S as the antioxidative compounds. In this study, we report the isolation, structural determination and 2,2-diphenyl-l-picrylhydrazyl radical scavenging activity of pyranonigrin E. We also investigated the biosynthesis of pyranonigrin A hi feeding experiments using sodium [l-13C]acetate, sodium [2-13C] acetate, sodium [1,2-13C2] acetate and [l-13C]glycine, and showed that it was composed of four units of acetate and one unit of glycine.