Waikikiamides A-C: Complex Diketopiperazine Dimer and Diketopiperazine-Polyketide Hybrids from a Hawaiian Marine Fungal Strain Aspergillus sp. FM242.

Waikikiamides A-C (1-3), structurally complex diketopiperazine derivatives, and putative biogenic precursors, (+)-semivioxanthin (4), notoamide F (5), and (-)-notoamide A (6), were isolated from Aspergillus sp. FM242. 1 and 2, bearing a hendecacyclic ring system, represent a novel skeleton. 3 features the first unique heterodimer of two notoamide analogs with an N-O-C bridge. Compounds 1 and 3 exhibit antiproliferative activity with IC50 values in the range of 0.56 to 1.86 μM. The gene clusters mined from the sequenced genome support their putative biosynthetic pathways.