Phomopsinamine is a potent mycotoxin produced by the fungus, Phomopsis leptostromiformis. Phomopsinamine is formed by hydrolysis of the dicarboxylic acid of phomopsin A. The phomopsins cause lupinosis in livestock fed infected lupins. Phomopsinamine is a potent microtubule inhibitor, blocking the polymerization of tubulin at a concentration of less than 1 µM by binding selectively to dimeric tubulin at a site overlapping that of vinblastine and maytansine.