Two new dioxopiperazine derivatives, arestrictins A and B, isolated from Aspergillus restrictus and Aspergillus penicilloides

In the course of searching for bioactive substances, two new dioxopiperazine derivatives, arestrictins A (1) and B (2), were isolated along with the known dioxopiperazine, cristatin A (3), and the known peptide, asperglucide (4), from the organic extract of the xerophilic fungi, Aspergillus restrictus and Aspergillus penicilloides. The absolute structures of 1 and 2, except for the configuration of the secondary alcohol in 1, were established by spectroscopic and chemical investigation. The absolute configuration of cristatin A (3) was also determined.