Depsidone and diaryl ether derivatives from the fungus Corynespora cassiicola, an endophyte of Gongronema latifolium

Chemical investigation of the ethyl acetate extract of Corynespora cassiicola, an endophytic fungus of Gongronema latifolium, afforded three new secondary metabolites, including corynesidone D (1), corynether B (2) and corynether lactone A (3), together with four known derivatives. The structures of the new compounds were deduced on the basis of 1D- and 2D-dimensional NMR spectroscopy as well as by high resolution mass spectrometry. Compounds 1 and 4–6 were tested for their ability to modulate the chaperoning activity of the Hsp90 chaperoning machine in vitro using 17-allylamino-demethoxygeldamycin (17-AAG) as a positive control. Unfortunately, no effect on the Hsp90 chaperoning machine has been observed.