Ophiobolins G and H: new fungal metabolites from a novel source, Aspergillus ustus

Two new metabolites, ophiobolin G (C sub(25)H sub(34)O sub(2)) and ophiobolin H (C sub(25)H sub(38)O sub(3)), were isolated from Aspergillus ustus). The structure of ophiobolin G was unequivocally established by single-crystal X-ray diffraction studies, whereas that of ophiobolin H was deduced from super(1)H and super(13)C NMR studies. Both compounds are unusual in that the ring fusion between rings A and B is trans (as opposed to cis in other fungal ophiobolins) and there is C16-C17 cis double bond. Both inhibited etiolated wheat coleoptile growth at 10 super(-3), 10 super(-4), and 10 super(-5) M. Both inhibited growth of Bacillus subtilis cultures, but ophiobolin H was a more potent inhibitor at rates above 250 mu g/disk than ophiobolin G. Neither inhibited growth of Escherichia coli . Ophiobolin H also induced hyperacusia in day-old chicks at rates up to 375 mg/kg, but there was no mortality.