Bicycloalternarenes produced by the phytopathogenic fungus Alternaria alternata.

Eleven compounds, ACTG toxins A and B and nine new substances named bicycloalternarenes (BCAs), were isolated and characterized from the culture filtrate of the phytopathogenic fungus Alternaria alternata. Under acidic conditions, these mixed terpenoids convert to pairs of tricycloaltenarenes that can be used for identification of the native compounds. We could not confirm the phytotoxic effects reported with ACTG-toxins in the past. However, BCA 2 at concentrations of 10(-4) M strongly inhibited germination and growth of Spirodela polyrhiza turions.