Asterriquinones produced by Aspergillus candidus inhibit binding of the Grb-2 adapter to phosphorylated EGF receptor tyrosine kinase

Five new asterriquinone analogs (2 similar to 4, 6, 7), together with previously identified neoasterriquinone (1) and isoasterriquinone (5), were isolated from a fermentation broth of the fungus Aspergillus candidus and purified by HSCCC (high speed counter current chromatography) followed by HPLC. The structures were determined by ID and 2D NMR and MS/MS techniques. All seven showed inhibitory activity against the binding of a recombinant protein containing the SH2 protein domain of Grb-2 to the tyrosine phosphorylated form of the EGF receptor tyrosine kinase. Some of these asterriquinones exhibited specific inhibition of Grb-2 binding compared to Grb-7 and PLC-gamma.