Probing Indole Diketopiperazine-Based Hybrids as Environmental-Induced Products from Aspergillus sp. EGF 15-0-3.

Comprehensive analyses of the metabolite spectra of Aspergillus sp. EGF 15-0-3 under different culture conditions revealed the presence of unique environmental-induced metabolites exclusively from the rice medium. Subsequent target isolation afforded four unprecedented indole diketopiperazine-based hybrids with a pyrano[3',2':7,8]isochromeno[4,3- b ]pyrazino[2,1- i ]indole core ( 1 and 2 ) or a spiro[piperazine-2,2'-pyrano[3,4,5- de ]chromene] scaffold ( 3 and 4 ). Putative biosynthetic pathways for 1 - 4 , with Diels-Alder cycloadditions as key steps, were proposed. 1 - 4 exhibited selective cytotoxicities among several human cancer cells.