Three unusual indole diketopiperazine alkaloids from a terrestrial-derived endophytic fungus, Aspergillus sp.

Three new indole diketopiperazine alkaloids, named aspertryptanthrins A-C (1-3), were isolated from a terrestrial-derived endophytic fungus Aspergillus sp. Their structures were established by spectral methods, and the absolute configurations were determined via the Rh-2(OCOCF3)(4) induced ECD spectra and the comparison of experimental and calculated ECD spectra. Belonging to the indole diketopiperazine alkaloids, these compounds represented first samples containing tryptanthrin skeleton formed by tryptophan residue and anthranilate unite, while aspertryptanthrin C (3) was particularly an interesting molecular skeleton containing a rare 16-membered ring. (C) 2015 Elsevier Ltd. All rights reserved.