Glionitrin B, a Cancer Invasion Inhibitory Diketopiperazine Produced by Microbial Coculture

A new diketopiperazine, glionitrin B (1), was produced using a microbial coculture of the fungus Aspergillus fumigatus KMC-901 and the bacterium Sphingomonas sp. KMK-001 that were isolated from acidic coal mine drainage. The structure of 1 was determined to be (3S,10aS)-dithiomethylglionitrin A. This structure was determined by the analyses of extensive NMR data and the circular dichroism spectra of the natural product and a semisynthetic compound derived from glionitrin A. In contrast to glionitrin A (2), glionitrin B (1) is not cytotoxic against the human prostate cancer cell line DU145. However, compound 1 caused suppression of DU145 cell invasion, producing 46% inhibition at 60 μM.