Secondary metabolites of a deep sea derived fungus Aspergillus versicolor CXCTD-06-6a and their bioactivity

In order to obtain novel secondary metabolites, a deep sea inhabiting fungus Aspergillus versicolor CXCTD-06-6a was investigated. One new diketopiperazine brevianamide W (1a), as well as five known diketopiperazine alkaloids, diketopiperazine V (1b), brevianamide Q (2), brevianamide R (3), brevianamide K (4), and brevianamide E (5), were isolated from the EtOAc extract of the fermentation broth. Their structures were elucidated by spectroscopy techniques (NMR, MS). The six compounds exhibited moderate radical scavenging activity against DPPH with clearance ratio of 55.0% (1a and 1b), 53.7% (2), 46.2% (3), 61.4% (4) and 19.3% (5) at a concentration of 13.9 μmol L−1, respectively; while the positive control ascorbic acid showed a ratio of 70.3% at the concentration of 28.4 μmol L−1.