A diketopiperazine dimer from a marine-derived isolate of Aspergillus niger

The new diketopiperazine dimer 1, as well as the known compounds TMC-256A1 (2), TMC-256C1 (3), and demethylkotanin (4), were isolated from a culture of Aspergillus niger. The gross structure of 1 was determined by 2D NMR studies and comparison with literature data, and the absolute stereochemistry was elucidated by chiral HPLC analysis of the hydrolysis products.